Services: Renamed from Servers

It didn't feel right to have a "DHCPClient" in a "Servers" directory.
Rename this to Services to better reflect the type of programs we'll
be putting in there.

Services/WindowServer/AppletManager.cpp

@@ -0,0 +1,135 @@
+/*
+ * Copyright (c) 2020-2020, Hüseyin Aslıtürk <asliturk@hotmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "AppletManager.h"
+#include <AK/QuickSort.h>
+#include <LibGfx/Painter.h>
+#include <WindowServer/MenuManager.h>
+
+namespace WindowServer {
+
+static AppletManager* s_the;
+Vector<String> order_vector;
+
+AppletManager::AppletManager()
+{
+    s_the = this;
+
+    auto wm_config = Core::ConfigFile::open("/etc/WindowServer/WindowServer.ini");
+    auto order = wm_config->read_entry("Applet", "Order");
+    order_vector = order.split(',');
+}
+
+AppletManager::~AppletManager()
+{
+}
+
+AppletManager& AppletManager::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
+void AppletManager::event(Core::Event& event)
+{
+    auto& mouse_event = static_cast<MouseEvent&>(event);
+
+    for (auto& applet : m_applets) {
+        if (!applet)
+            continue;
+        if (!applet->rect_in_menubar().contains(mouse_event.position()))
+            continue;
+        auto local_event = mouse_event.translated(-applet->rect_in_menubar().location());
+        applet->event(local_event);
+    }
+}
+
+void AppletManager::add_applet(Window& applet)
+{
+    m_applets.append(applet.make_weak_ptr());
+
+    // Prune any dead weak pointers from the applet list.
+    m_applets.remove_all_matching([](auto& entry) {
+        return entry.is_null();
+    });
+
+    quick_sort(m_applets, [](auto& a, auto& b) {
+        auto index_a = order_vector.find_first_index(a->title());
+        auto index_b = order_vector.find_first_index(b->title());
+        return index_a.value_or(0) > index_b.value_or(0);
+    });
+
+    calculate_applet_rects(MenuManager::the().window());
+}
+
+void AppletManager::calculate_applet_rects(Window& window)
+{
+    auto menubar_rect = window.rect();
+    int right_edge_x = menubar_rect.width() - 4;
+    for (auto& existing_applet : m_applets) {
+
+        Gfx::Rect new_applet_rect(right_edge_x - existing_applet->size().width(), 0, existing_applet->size().width(), existing_applet->size().height());
+        Gfx::Rect dummy_menubar_rect(0, 0, 0, 18);
+        new_applet_rect.center_vertically_within(dummy_menubar_rect);
+
+        existing_applet->set_rect_in_menubar(new_applet_rect);
+        right_edge_x = existing_applet->rect_in_menubar().x() - 4;
+    }
+}
+
+void AppletManager::remove_applet(Window& applet)
+{
+    m_applets.remove_first_matching([&](auto& entry) {
+        return &applet == entry.ptr();
+    });
+}
+
+void AppletManager::draw()
+{
+    for (auto& applet : m_applets) {
+        if (!applet)
+            continue;
+        draw_applet(*applet);
+    }
+}
+
+void AppletManager::draw_applet(const Window& applet)
+{
+    if (!applet.backing_store())
+        return;
+
+    Gfx::Painter painter(*MenuManager::the().window().backing_store());
+    painter.fill_rect(applet.rect_in_menubar(), WindowManager::the().palette().window());
+    painter.blit(applet.rect_in_menubar().location(), *applet.backing_store(), applet.backing_store()->rect());
+}
+
+void AppletManager::invalidate_applet(const Window& applet, const Gfx::Rect& rect)
+{
+    draw_applet(applet);
+    MenuManager::the().window().invalidate(rect.translated(applet.rect_in_menubar().location()));
+}
+
+}

Services/WindowServer/AppletManager.h

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2020-2020, Hüseyin Aslıtürk <asliturk@hotmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <WindowServer/Window.h>
+#include <WindowServer/WindowManager.h>
+
+namespace WindowServer {
+
+class AppletManager : public Core::Object {
+    C_OBJECT(AppletManager)
+public:
+    AppletManager();
+    ~AppletManager();
+
+    static AppletManager& the();
+
+    virtual void event(Core::Event&) override;
+
+    void add_applet(Window& applet);
+    void remove_applet(Window& applet);
+    void draw();
+    void invalidate_applet(const Window& applet, const Gfx::Rect& rect);
+    void calculate_applet_rects(Window& window);
+
+private:
+    void draw_applet(const Window& applet);
+
+    Vector<WeakPtr<Window>> m_applets;
+};
+
+}

Services/WindowServer/Button.cpp

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <LibGfx/CharacterBitmap.h>
+#include <LibGfx/Painter.h>
+#include <LibGfx/StylePainter.h>
+#include <WindowServer/Button.h>
+#include <WindowServer/Event.h>
+#include <WindowServer/WindowManager.h>
+
+namespace WindowServer {
+
+Button::Button(WindowFrame& frame, NonnullRefPtr<Gfx::CharacterBitmap>&& bitmap, Function<void(Button&)>&& on_click_handler)
+    : on_click(move(on_click_handler))
+    , m_frame(frame)
+    , m_bitmap(move(bitmap))
+{
+}
+
+Button::~Button()
+{
+}
+
+void Button::paint(Gfx::Painter& painter)
+{
+    auto palette = WindowManager::the().palette();
+    Gfx::PainterStateSaver saver(painter);
+    painter.translate(relative_rect().location());
+    Gfx::StylePainter::paint_button(painter, rect(), palette, Gfx::ButtonStyle::Normal, m_pressed, m_hovered);
+    auto x_location = rect().center();
+    x_location.move_by(-(m_bitmap->width() / 2), -(m_bitmap->height() / 2));
+    if (m_pressed)
+        x_location.move_by(1, 1);
+    painter.draw_bitmap(x_location, *m_bitmap, palette.button_text());
+}
+
+void Button::on_mouse_event(const MouseEvent& event)
+{
+    auto& wm = WindowManager::the();
+
+    if (event.type() == Event::MouseDown && event.button() == MouseButton::Left) {
+        m_pressed = true;
+        wm.set_cursor_tracking_button(this);
+        wm.invalidate(screen_rect());
+        return;
+    }
+
+    if (event.type() == Event::MouseUp && event.button() == MouseButton::Left) {
+        if (wm.cursor_tracking_button() != this)
+            return;
+        wm.set_cursor_tracking_button(nullptr);
+        bool old_pressed = m_pressed;
+        m_pressed = false;
+        if (rect().contains(event.position())) {
+            if (on_click)
+                on_click(*this);
+        }
+        if (old_pressed != m_pressed) {
+            // Would like to compute:
+            // m_hovered = rect_after_action().contains(event.position());
+            // However, we don't know that rect yet. We can make an educated
+            // guess which also looks okay even when wrong:
+            m_hovered = false;
+            wm.invalidate(screen_rect());
+        }
+        return;
+    }
+
+    if (event.type() == Event::MouseMove) {
+        bool old_hovered = m_hovered;
+        m_hovered = rect().contains(event.position());
+        wm.set_hovered_button(m_hovered ? this : nullptr);
+        if (old_hovered != m_hovered)
+            wm.invalidate(screen_rect());
+    }
+
+    if (event.type() == Event::MouseMove && event.buttons() & (unsigned)MouseButton::Left) {
+        if (wm.cursor_tracking_button() != this)
+            return;
+        bool old_pressed = m_pressed;
+        m_pressed = m_hovered;
+        if (old_pressed != m_pressed)
+            wm.invalidate(screen_rect());
+    }
+}
+
+Gfx::Rect Button::screen_rect() const
+{
+    return m_relative_rect.translated(m_frame.rect().location());
+}
+
+}

Services/WindowServer/Button.h

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/NonnullRefPtr.h>
+#include <AK/Weakable.h>
+#include <LibGfx/Rect.h>
+#include <LibGfx/Forward.h>
+
+namespace WindowServer {
+
+class MouseEvent;
+class WindowFrame;
+
+class Button : public Weakable<Button> {
+public:
+    Button(WindowFrame&, NonnullRefPtr<Gfx::CharacterBitmap>&&, Function<void(Button&)>&& on_click_handler);
+    ~Button();
+
+    Gfx::Rect relative_rect() const { return m_relative_rect; }
+    void set_relative_rect(const Gfx::Rect& rect) { m_relative_rect = rect; }
+
+    Gfx::Rect rect() const { return { {}, m_relative_rect.size() }; }
+    Gfx::Rect screen_rect() const;
+
+    void paint(Gfx::Painter&);
+
+    void on_mouse_event(const MouseEvent&);
+
+    Function<void(Button&)> on_click;
+
+    bool is_visible() const { return m_visible; }
+
+    void set_bitmap(const Gfx::CharacterBitmap& bitmap) { m_bitmap = bitmap; }
+
+private:
+    WindowFrame& m_frame;
+    Gfx::Rect m_relative_rect;
+    NonnullRefPtr<Gfx::CharacterBitmap> m_bitmap;
+    bool m_pressed { false };
+    bool m_visible { true };
+    bool m_hovered { false };
+};
+
+}

Services/WindowServer/ClientConnection.cpp

@@ -0,0 +1,833 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Badge.h>
+#include <AK/SharedBuffer.h>
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/SystemTheme.h>
+#include <WindowServer/AppletManager.h>
+#include <WindowServer/ClientConnection.h>
+#include <WindowServer/Clipboard.h>
+#include <WindowServer/Compositor.h>
+#include <WindowServer/EventLoop.h>
+#include <WindowServer/Menu.h>
+#include <WindowServer/MenuBar.h>
+#include <WindowServer/MenuItem.h>
+#include <WindowServer/Screen.h>
+#include <WindowServer/Window.h>
+#include <WindowServer/WindowClientEndpoint.h>
+#include <WindowServer/WindowManager.h>
+#include <WindowServer/WindowSwitcher.h>
+#include <errno.h>
+#include <serenity.h>
+#include <stdio.h>
+#include <unistd.h>
+
+namespace WindowServer {
+
+HashMap<int, NonnullRefPtr<ClientConnection>>* s_connections;
+
+static Gfx::Rect normalize_window_rect(Gfx::Rect rect, WindowType window_type)
+{
+    auto min_size = 1;
+    if (window_type == WindowType::Normal)
+        min_size = 50;
+    Gfx::Rect normalized_rect = { rect.x(), rect.y(), max(rect.width(), min_size), max(rect.height(), min_size) };
+    return normalized_rect;
+}
+
+void ClientConnection::for_each_client(Function<void(ClientConnection&)> callback)
+{
+    if (!s_connections)
+        return;
+    for (auto& it : *s_connections) {
+        callback(*it.value);
+    }
+}
+
+ClientConnection* ClientConnection::from_client_id(int client_id)
+{
+    if (!s_connections)
+        return nullptr;
+    auto it = s_connections->find(client_id);
+    if (it == s_connections->end())
+        return nullptr;
+    return (*it).value.ptr();
+}
+
+ClientConnection::ClientConnection(Core::LocalSocket& client_socket, int client_id)
+    : IPC::ClientConnection<WindowServerEndpoint>(*this, client_socket, client_id)
+{
+    if (!s_connections)
+        s_connections = new HashMap<int, NonnullRefPtr<ClientConnection>>;
+    s_connections->set(client_id, *this);
+}
+
+ClientConnection::~ClientConnection()
+{
+    if (m_has_display_link)
+        Compositor::the().decrement_display_link_count({});
+
+    MenuManager::the().close_all_menus_from_client({}, *this);
+    auto windows = move(m_windows);
+    for (auto& window : windows) {
+        window.value->detach_client({});
+        if (window.value->type() == WindowType::MenuApplet)
+            AppletManager::the().remove_applet(window.value);
+    }
+}
+
+void ClientConnection::die()
+{
+    deferred_invoke([this](auto&) {
+        s_connections->remove(client_id());
+    });
+}
+
+void ClientConnection::notify_about_new_screen_rect(const Gfx::Rect& rect)
+{
+    post_message(Messages::WindowClient::ScreenRectChanged(rect));
+}
+
+void ClientConnection::notify_about_clipboard_contents_changed()
+{
+    post_message(Messages::WindowClient::ClipboardContentsChanged(Clipboard::the().data_type()));
+}
+
+OwnPtr<Messages::WindowServer::CreateMenubarResponse> ClientConnection::handle(const Messages::WindowServer::CreateMenubar&)
+{
+    int menubar_id = m_next_menubar_id++;
+    auto menubar = make<MenuBar>(*this, menubar_id);
+    m_menubars.set(menubar_id, move(menubar));
+    return make<Messages::WindowServer::CreateMenubarResponse>(menubar_id);
+}
+
+OwnPtr<Messages::WindowServer::DestroyMenubarResponse> ClientConnection::handle(const Messages::WindowServer::DestroyMenubar& message)
+{
+    int menubar_id = message.menubar_id();
+    auto it = m_menubars.find(menubar_id);
+    if (it == m_menubars.end()) {
+        did_misbehave("DestroyMenubar: Bad menubar ID");
+        return nullptr;
+    }
+    auto& menubar = *(*it).value;
+    MenuManager::the().close_menubar(menubar);
+    m_menubars.remove(it);
+    return make<Messages::WindowServer::DestroyMenubarResponse>();
+}
+
+OwnPtr<Messages::WindowServer::CreateMenuResponse> ClientConnection::handle(const Messages::WindowServer::CreateMenu& message)
+{
+    int menu_id = m_next_menu_id++;
+    auto menu = Menu::construct(this, menu_id, message.menu_title());
+    m_menus.set(menu_id, move(menu));
+    return make<Messages::WindowServer::CreateMenuResponse>(menu_id);
+}
+
+OwnPtr<Messages::WindowServer::DestroyMenuResponse> ClientConnection::handle(const Messages::WindowServer::DestroyMenu& message)
+{
+    int menu_id = message.menu_id();
+    auto it = m_menus.find(menu_id);
+    if (it == m_menus.end()) {
+        did_misbehave("DestroyMenu: Bad menu ID");
+        return nullptr;
+    }
+    auto& menu = *(*it).value;
+    menu.close();
+    m_menus.remove(it);
+    remove_child(menu);
+    return make<Messages::WindowServer::DestroyMenuResponse>();
+}
+
+OwnPtr<Messages::WindowServer::SetApplicationMenubarResponse> ClientConnection::handle(const Messages::WindowServer::SetApplicationMenubar& message)
+{
+    int menubar_id = message.menubar_id();
+    auto it = m_menubars.find(menubar_id);
+    if (it == m_menubars.end()) {
+        did_misbehave("SetApplicationMenubar: Bad menubar ID");
+        return nullptr;
+    }
+    auto& menubar = *(*it).value;
+    m_app_menubar = menubar.make_weak_ptr();
+    WindowManager::the().notify_client_changed_app_menubar(*this);
+    return make<Messages::WindowServer::SetApplicationMenubarResponse>();
+}
+
+OwnPtr<Messages::WindowServer::AddMenuToMenubarResponse> ClientConnection::handle(const Messages::WindowServer::AddMenuToMenubar& message)
+{
+    int menubar_id = message.menubar_id();
+    int menu_id = message.menu_id();
+    auto it = m_menubars.find(menubar_id);
+    auto jt = m_menus.find(menu_id);
+    if (it == m_menubars.end()) {
+        did_misbehave("AddMenuToMenubar: Bad menubar ID");
+        return nullptr;
+    }
+    if (jt == m_menus.end()) {
+        did_misbehave("AddMenuToMenubar: Bad menu ID");
+        return nullptr;
+    }
+    auto& menubar = *(*it).value;
+    auto& menu = *(*jt).value;
+    menubar.add_menu(menu);
+    return make<Messages::WindowServer::AddMenuToMenubarResponse>();
+}
+
+OwnPtr<Messages::WindowServer::AddMenuItemResponse> ClientConnection::handle(const Messages::WindowServer::AddMenuItem& message)
+{
+    int menu_id = message.menu_id();
+    unsigned identifier = message.identifier();
+    auto it = m_menus.find(menu_id);
+    if (it == m_menus.end()) {
+        dbg() << "AddMenuItem: Bad menu ID: " << menu_id;
+        return nullptr;
+    }
+    auto& menu = *(*it).value;
+    auto menu_item = make<MenuItem>(menu, identifier, message.text(), message.shortcut(), message.enabled(), message.checkable(), message.checked());
+    if (message.icon_buffer_id() != -1) {
+        auto icon_buffer = SharedBuffer::create_from_shbuf_id(message.icon_buffer_id());
+        if (!icon_buffer)
+            return nullptr;
+        // FIXME: Verify that the icon buffer can accomodate a 16x16 bitmap view.
+        auto shared_icon = Gfx::Bitmap::create_with_shared_buffer(Gfx::BitmapFormat::RGBA32, icon_buffer.release_nonnull(), { 16, 16 });
+        menu_item->set_icon(shared_icon);
+    }
+    menu_item->set_submenu_id(message.submenu_id());
+    menu_item->set_exclusive(message.exclusive());
+    menu.add_item(move(menu_item));
+    return make<Messages::WindowServer::AddMenuItemResponse>();
+}
+
+OwnPtr<Messages::WindowServer::PopupMenuResponse> ClientConnection::handle(const Messages::WindowServer::PopupMenu& message)
+{
+    int menu_id = message.menu_id();
+    auto position = message.screen_position();
+    auto it = m_menus.find(menu_id);
+    if (it == m_menus.end()) {
+        did_misbehave("PopupMenu: Bad menu ID");
+        return nullptr;
+    }
+    auto& menu = *(*it).value;
+    menu.popup(position);
+    return make<Messages::WindowServer::PopupMenuResponse>();
+}
+
+OwnPtr<Messages::WindowServer::DismissMenuResponse> ClientConnection::handle(const Messages::WindowServer::DismissMenu& message)
+{
+    int menu_id = message.menu_id();
+    auto it = m_menus.find(menu_id);
+    if (it == m_menus.end()) {
+        did_misbehave("DismissMenu: Bad menu ID");
+        return nullptr;
+    }
+    auto& menu = *(*it).value;
+    menu.close();
+    return make<Messages::WindowServer::DismissMenuResponse>();
+}
+
+OwnPtr<Messages::WindowServer::UpdateMenuItemResponse> ClientConnection::handle(const Messages::WindowServer::UpdateMenuItem& message)
+{
+    int menu_id = message.menu_id();
+    auto it = m_menus.find(menu_id);
+    if (it == m_menus.end()) {
+        did_misbehave("UpdateMenuItem: Bad menu ID");
+        return nullptr;
+    }
+    auto& menu = *(*it).value;
+    auto* menu_item = menu.item_with_identifier(message.identifier());
+    if (!menu_item) {
+        did_misbehave("UpdateMenuItem: Bad menu item identifier");
+        return nullptr;
+    }
+    menu_item->set_text(message.text());
+    menu_item->set_shortcut_text(message.shortcut());
+    menu_item->set_enabled(message.enabled());
+    menu_item->set_checkable(message.checkable());
+    if (message.checkable())
+        menu_item->set_checked(message.checked());
+    return make<Messages::WindowServer::UpdateMenuItemResponse>();
+}
+
+OwnPtr<Messages::WindowServer::AddMenuSeparatorResponse> ClientConnection::handle(const Messages::WindowServer::AddMenuSeparator& message)
+{
+    int menu_id = message.menu_id();
+    auto it = m_menus.find(menu_id);
+    if (it == m_menus.end()) {
+        did_misbehave("AddMenuSeparator: Bad menu ID");
+        return nullptr;
+    }
+    auto& menu = *(*it).value;
+    menu.add_item(make<MenuItem>(menu, MenuItem::Separator));
+    return make<Messages::WindowServer::AddMenuSeparatorResponse>();
+}
+
+OwnPtr<Messages::WindowServer::MoveWindowToFrontResponse> ClientConnection::handle(const Messages::WindowServer::MoveWindowToFront& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("MoveWindowToFront: Bad window ID");
+        return nullptr;
+    }
+    WindowManager::the().move_to_front_and_make_active(*(*it).value);
+    return make<Messages::WindowServer::MoveWindowToFrontResponse>();
+}
+
+OwnPtr<Messages::WindowServer::SetFullscreenResponse> ClientConnection::handle(const Messages::WindowServer::SetFullscreen& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("SetFullscreen: Bad window ID");
+        return nullptr;
+    }
+    it->value->set_fullscreen(message.fullscreen());
+    return make<Messages::WindowServer::SetFullscreenResponse>();
+}
+
+OwnPtr<Messages::WindowServer::SetWindowOpacityResponse> ClientConnection::handle(const Messages::WindowServer::SetWindowOpacity& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("SetWindowOpacity: Bad window ID");
+        return nullptr;
+    }
+    it->value->set_opacity(message.opacity());
+    return make<Messages::WindowServer::SetWindowOpacityResponse>();
+}
+
+void ClientConnection::handle(const Messages::WindowServer::AsyncSetWallpaper& message)
+{
+    Compositor::the().set_wallpaper(message.path(), [&](bool success) {
+        post_message(Messages::WindowClient::AsyncSetWallpaperFinished(success));
+    });
+}
+
+OwnPtr<Messages::WindowServer::SetBackgroundColorResponse> ClientConnection::handle(const Messages::WindowServer::SetBackgroundColor& message)
+{
+    Compositor::the().set_background_color(message.background_color());
+    return make<Messages::WindowServer::SetBackgroundColorResponse>();
+}
+
+OwnPtr<Messages::WindowServer::SetWallpaperModeResponse> ClientConnection::handle(const Messages::WindowServer::SetWallpaperMode& message)
+{
+    Compositor::the().set_wallpaper_mode(message.mode());
+    return make<Messages::WindowServer::SetWallpaperModeResponse>();
+}
+
+OwnPtr<Messages::WindowServer::GetWallpaperResponse> ClientConnection::handle(const Messages::WindowServer::GetWallpaper&)
+{
+    return make<Messages::WindowServer::GetWallpaperResponse>(Compositor::the().wallpaper_path());
+}
+
+OwnPtr<Messages::WindowServer::SetResolutionResponse> ClientConnection::handle(const Messages::WindowServer::SetResolution& message)
+{
+    return make<Messages::WindowServer::SetResolutionResponse>(WindowManager::the().set_resolution(message.resolution().width(), message.resolution().height()), WindowManager::the().resolution());
+}
+
+OwnPtr<Messages::WindowServer::SetWindowTitleResponse> ClientConnection::handle(const Messages::WindowServer::SetWindowTitle& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("SetWindowTitle: Bad window ID");
+        return nullptr;
+    }
+    it->value->set_title(message.title());
+    return make<Messages::WindowServer::SetWindowTitleResponse>();
+}
+
+OwnPtr<Messages::WindowServer::GetWindowTitleResponse> ClientConnection::handle(const Messages::WindowServer::GetWindowTitle& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("GetWindowTitle: Bad window ID");
+        return nullptr;
+    }
+    return make<Messages::WindowServer::GetWindowTitleResponse>(it->value->title());
+}
+
+OwnPtr<Messages::WindowServer::SetWindowIconBitmapResponse> ClientConnection::handle(const Messages::WindowServer::SetWindowIconBitmap& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("SetWindowIconBitmap: Bad window ID");
+        return nullptr;
+    }
+    auto& window = *(*it).value;
+
+    if (message.icon().is_valid()) {
+        window.set_icon(*message.icon().bitmap());
+    } else {
+        window.set_default_icon();
+    }
+
+    window.frame().invalidate_title_bar();
+    WindowManager::the().tell_wm_listeners_window_icon_changed(window);
+    return make<Messages::WindowServer::SetWindowIconBitmapResponse>();
+}
+
+OwnPtr<Messages::WindowServer::SetWindowRectResponse> ClientConnection::handle(const Messages::WindowServer::SetWindowRect& message)
+{
+    int window_id = message.window_id();
+    auto it = m_windows.find(window_id);
+    if (it == m_windows.end()) {
+        did_misbehave("SetWindowRect: Bad window ID");
+        return nullptr;
+    }
+    auto& window = *(*it).value;
+    if (window.is_fullscreen()) {
+        dbg() << "ClientConnection: Ignoring SetWindowRect request for fullscreen window";
+        return nullptr;
+    }
+    auto normalized_rect = normalize_window_rect(message.rect(), window.type());
+    window.set_rect(normalized_rect);
+    window.request_update(normalized_rect);
+    return make<Messages::WindowServer::SetWindowRectResponse>(normalized_rect);
+}
+
+OwnPtr<Messages::WindowServer::GetWindowRectResponse> ClientConnection::handle(const Messages::WindowServer::GetWindowRect& message)
+{
+    int window_id = message.window_id();
+    auto it = m_windows.find(window_id);
+    if (it == m_windows.end()) {
+        did_misbehave("GetWindowRect: Bad window ID");
+        return nullptr;
+    }
+    return make<Messages::WindowServer::GetWindowRectResponse>(it->value->rect());
+}
+
+OwnPtr<Messages::WindowServer::SetClipboardContentsResponse> ClientConnection::handle(const Messages::WindowServer::SetClipboardContents& message)
+{
+    auto shared_buffer = SharedBuffer::create_from_shbuf_id(message.shbuf_id());
+    if (!shared_buffer) {
+        did_misbehave("SetClipboardContents: Bad shared buffer ID");
+        return nullptr;
+    }
+    Clipboard::the().set_data(*shared_buffer, message.content_size(), message.content_type());
+    return make<Messages::WindowServer::SetClipboardContentsResponse>();
+}
+
+OwnPtr<Messages::WindowServer::GetClipboardContentsResponse> ClientConnection::handle(const Messages::WindowServer::GetClipboardContents&)
+{
+    auto& clipboard = Clipboard::the();
+
+    i32 shbuf_id = -1;
+    if (clipboard.size()) {
+        // FIXME: Optimize case where an app is copy/pasting within itself.
+        //        We can just reuse the SharedBuffer then, since it will have the same peer PID.
+        //        It would be even nicer if a SharedBuffer could have an arbitrary number of clients..
+        RefPtr<SharedBuffer> shared_buffer = SharedBuffer::create_with_size(clipboard.size());
+        ASSERT(shared_buffer);
+        memcpy(shared_buffer->data(), clipboard.data(), clipboard.size());
+        shared_buffer->seal();
+        shared_buffer->share_with(client_pid());
+        shbuf_id = shared_buffer->shbuf_id();
+
+        // FIXME: This is a workaround for the fact that SharedBuffers will go away if neither side is retaining them.
+        //        After we respond to GetClipboardContents, we have to wait for the client to ref the buffer on his side.
+        m_last_sent_clipboard_content = move(shared_buffer);
+    }
+    return make<Messages::WindowServer::GetClipboardContentsResponse>(shbuf_id, clipboard.size(), clipboard.data_type());
+}
+
+Window* ClientConnection::window_from_id(i32 window_id)
+{
+    auto it = m_windows.find(window_id);
+    if (it == m_windows.end())
+        return nullptr;
+    return it->value.ptr();
+}
+
+OwnPtr<Messages::WindowServer::CreateWindowResponse> ClientConnection::handle(const Messages::WindowServer::CreateWindow& message)
+{
+    int window_id = m_next_window_id++;
+    auto window = Window::construct(*this, (WindowType)message.type(), window_id, message.modal(), message.minimizable(), message.frameless(), message.resizable(), message.fullscreen());
+
+    if (message.parent_window_id()) {
+        auto* parent_window = window_from_id(message.parent_window_id());
+        if (!parent_window) {
+            did_misbehave("CreateWindow with bad parent_window_id");
+            return nullptr;
+        }
+        if (parent_window->window_id() == window_id) {
+            did_misbehave("CreateWindow trying to make a window with itself as parent");
+            return nullptr;
+        }
+        window->set_parent_window(*parent_window);
+    }
+
+    window->set_has_alpha_channel(message.has_alpha_channel());
+    window->set_title(message.title());
+    if (!message.fullscreen()) {
+        auto normalized_rect = normalize_window_rect(message.rect(), window->type());
+        window->set_rect(normalized_rect);
+    }
+    if (window->type() == WindowType::Desktop) {
+        window->set_rect(WindowManager::the().desktop_rect());
+        window->recalculate_rect();
+    }
+    window->set_opacity(message.opacity());
+    window->set_size_increment(message.size_increment());
+    window->set_base_size(message.base_size());
+    window->invalidate();
+    if (window->type() == WindowType::MenuApplet)
+        AppletManager::the().add_applet(*window);
+    m_windows.set(window_id, move(window));
+    return make<Messages::WindowServer::CreateWindowResponse>(window_id);
+}
+
+void ClientConnection::destroy_window(Window& window, Vector<i32>& destroyed_window_ids)
+{
+    for (auto& child_window : window.child_windows()) {
+        if (!child_window)
+            continue;
+        ASSERT(child_window->window_id() != window.window_id());
+        destroy_window(*child_window, destroyed_window_ids);
+    }
+
+    destroyed_window_ids.append(window.window_id());
+
+    if (window.type() == WindowType::MenuApplet)
+        AppletManager::the().remove_applet(window);
+
+    WindowManager::the().invalidate(window);
+    remove_child(window);
+    m_windows.remove(window.window_id());
+}
+
+OwnPtr<Messages::WindowServer::DestroyWindowResponse> ClientConnection::handle(const Messages::WindowServer::DestroyWindow& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("DestroyWindow: Bad window ID");
+        return nullptr;
+    }
+    auto& window = *(*it).value;
+    Vector<i32> destroyed_window_ids;
+    destroy_window(window, destroyed_window_ids);
+    return make<Messages::WindowServer::DestroyWindowResponse>(destroyed_window_ids);
+}
+
+void ClientConnection::post_paint_message(Window& window, bool ignore_occlusion)
+{
+    auto rect_set = window.take_pending_paint_rects();
+    if (window.is_minimized() || (!ignore_occlusion && window.is_occluded()))
+        return;
+
+    post_message(Messages::WindowClient::Paint(window.window_id(), window.size(), rect_set.rects()));
+}
+
+void ClientConnection::handle(const Messages::WindowServer::InvalidateRect& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("InvalidateRect: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    for (size_t i = 0; i < message.rects().size(); ++i)
+        window.request_update(message.rects()[i].intersected({ {}, window.size() }), message.ignore_occlusion());
+}
+
+void ClientConnection::handle(const Messages::WindowServer::DidFinishPainting& message)
+{
+    int window_id = message.window_id();
+    auto it = m_windows.find(window_id);
+    if (it == m_windows.end()) {
+        did_misbehave("DidFinishPainting: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    for (auto& rect : message.rects())
+        WindowManager::the().invalidate(window, rect);
+
+    WindowSwitcher::the().refresh_if_needed();
+}
+
+OwnPtr<Messages::WindowServer::SetWindowBackingStoreResponse> ClientConnection::handle(const Messages::WindowServer::SetWindowBackingStore& message)
+{
+    int window_id = message.window_id();
+    auto it = m_windows.find(window_id);
+    if (it == m_windows.end()) {
+        did_misbehave("SetWindowBackingStore: Bad window ID");
+        return nullptr;
+    }
+    auto& window = *(*it).value;
+    if (window.last_backing_store() && window.last_backing_store()->shbuf_id() == message.shbuf_id()) {
+        window.swap_backing_stores();
+    } else {
+        auto shared_buffer = SharedBuffer::create_from_shbuf_id(message.shbuf_id());
+        if (!shared_buffer)
+            return make<Messages::WindowServer::SetWindowBackingStoreResponse>();
+        auto backing_store = Gfx::Bitmap::create_with_shared_buffer(
+            message.has_alpha_channel() ? Gfx::BitmapFormat::RGBA32 : Gfx::BitmapFormat::RGB32,
+            *shared_buffer,
+            message.size());
+        window.set_backing_store(move(backing_store));
+    }
+
+    if (message.flush_immediately())
+        window.invalidate();
+
+    return make<Messages::WindowServer::SetWindowBackingStoreResponse>();
+}
+
+OwnPtr<Messages::WindowServer::SetGlobalCursorTrackingResponse> ClientConnection::handle(const Messages::WindowServer::SetGlobalCursorTracking& message)
+{
+    int window_id = message.window_id();
+    auto it = m_windows.find(window_id);
+    if (it == m_windows.end()) {
+        did_misbehave("SetGlobalCursorTracking: Bad window ID");
+        return nullptr;
+    }
+    it->value->set_global_cursor_tracking_enabled(message.enabled());
+    return make<Messages::WindowServer::SetGlobalCursorTrackingResponse>();
+}
+
+OwnPtr<Messages::WindowServer::SetWindowOverrideCursorResponse> ClientConnection::handle(const Messages::WindowServer::SetWindowOverrideCursor& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("SetWindowOverrideCursor: Bad window ID");
+        return nullptr;
+    }
+    auto& window = *(*it).value;
+    window.set_override_cursor(Cursor::create((StandardCursor)message.cursor_type()));
+    return make<Messages::WindowServer::SetWindowOverrideCursorResponse>();
+}
+
+OwnPtr<Messages::WindowServer::SetWindowHasAlphaChannelResponse> ClientConnection::handle(const Messages::WindowServer::SetWindowHasAlphaChannel& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("SetWindowHasAlphaChannel: Bad window ID");
+        return nullptr;
+    }
+    it->value->set_has_alpha_channel(message.has_alpha_channel());
+    return make<Messages::WindowServer::SetWindowHasAlphaChannelResponse>();
+}
+
+void ClientConnection::handle(const Messages::WindowServer::WM_SetActiveWindow& message)
+{
+    auto* client = ClientConnection::from_client_id(message.client_id());
+    if (!client) {
+        did_misbehave("WM_SetActiveWindow: Bad client ID");
+        return;
+    }
+    auto it = client->m_windows.find(message.window_id());
+    if (it == client->m_windows.end()) {
+        did_misbehave("WM_SetActiveWindow: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    window.set_minimized(false);
+    WindowManager::the().move_to_front_and_make_active(window);
+}
+
+void ClientConnection::handle(const Messages::WindowServer::WM_PopupWindowMenu& message)
+{
+    auto* client = ClientConnection::from_client_id(message.client_id());
+    if (!client) {
+        did_misbehave("WM_PopupWindowMenu: Bad client ID");
+        return;
+    }
+    auto it = client->m_windows.find(message.window_id());
+    if (it == client->m_windows.end()) {
+        did_misbehave("WM_PopupWindowMenu: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    window.popup_window_menu(message.screen_position());
+}
+
+void ClientConnection::handle(const Messages::WindowServer::WM_StartWindowResize& request)
+{
+    auto* client = ClientConnection::from_client_id(request.client_id());
+    if (!client) {
+        did_misbehave("WM_StartWindowResize: Bad client ID");
+        return;
+    }
+    auto it = client->m_windows.find(request.window_id());
+    if (it == client->m_windows.end()) {
+        did_misbehave("WM_StartWindowResize: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    // FIXME: We are cheating a bit here by using the current cursor location and hard-coding the left button.
+    //        Maybe the client should be allowed to specify what initiated this request?
+    WindowManager::the().start_window_resize(window, Screen::the().cursor_location(), MouseButton::Left);
+}
+
+void ClientConnection::handle(const Messages::WindowServer::WM_SetWindowMinimized& message)
+{
+    auto* client = ClientConnection::from_client_id(message.client_id());
+    if (!client) {
+        did_misbehave("WM_SetWindowMinimized: Bad client ID");
+        return;
+    }
+    auto it = client->m_windows.find(message.window_id());
+    if (it == client->m_windows.end()) {
+        did_misbehave("WM_SetWindowMinimized: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    window.set_minimized(message.minimized());
+}
+
+OwnPtr<Messages::WindowServer::GreetResponse> ClientConnection::handle(const Messages::WindowServer::Greet&)
+{
+    return make<Messages::WindowServer::GreetResponse>(client_id(), Screen::the().rect(), Gfx::current_system_theme_buffer_id());
+}
+
+bool ClientConnection::is_showing_modal_window() const
+{
+    for (auto& it : m_windows) {
+        auto& window = *it.value;
+        if (window.is_visible() && window.is_modal())
+            return true;
+    }
+    return false;
+}
+
+void ClientConnection::handle(const Messages::WindowServer::WM_SetWindowTaskbarRect& message)
+{
+    auto* client = ClientConnection::from_client_id(message.client_id());
+    if (!client) {
+        did_misbehave("WM_SetWindowTaskbarRect: Bad client ID");
+        return;
+    }
+    auto it = client->m_windows.find(message.window_id());
+    if (it == client->m_windows.end()) {
+        did_misbehave("WM_SetWindowTaskbarRect: Bad window ID");
+        return;
+    }
+    auto& window = *(*it).value;
+    window.set_taskbar_rect(message.rect());
+}
+
+OwnPtr<Messages::WindowServer::StartDragResponse> ClientConnection::handle(const Messages::WindowServer::StartDrag& message)
+{
+    auto& wm = WindowManager::the();
+    if (wm.dnd_client())
+        return make<Messages::WindowServer::StartDragResponse>(false);
+
+    RefPtr<Gfx::Bitmap> bitmap;
+    if (message.bitmap_id() != -1) {
+        auto shared_buffer = SharedBuffer::create_from_shbuf_id(message.bitmap_id());
+        ssize_t size_in_bytes = message.bitmap_size().area() * sizeof(Gfx::RGBA32);
+        if (size_in_bytes > shared_buffer->size()) {
+            did_misbehave("SetAppletBackingStore: Shared buffer is too small for applet size");
+            return nullptr;
+        }
+        bitmap = Gfx::Bitmap::create_with_shared_buffer(Gfx::BitmapFormat::RGBA32, *shared_buffer, message.bitmap_size());
+    }
+
+    wm.start_dnd_drag(*this, message.text(), bitmap, message.data_type(), message.data());
+    return make<Messages::WindowServer::StartDragResponse>(true);
+}
+
+OwnPtr<Messages::WindowServer::SetSystemMenuResponse> ClientConnection::handle(const Messages::WindowServer::SetSystemMenu& message)
+{
+    auto it = m_menus.find(message.menu_id());
+    if (it == m_menus.end()) {
+        did_misbehave("SetSystemMenu called with invalid menu ID");
+        return nullptr;
+    }
+
+    auto& menu = it->value;
+    MenuManager::the().set_system_menu(menu);
+    return make<Messages::WindowServer::SetSystemMenuResponse>();
+}
+
+OwnPtr<Messages::WindowServer::SetSystemThemeResponse> ClientConnection::handle(const Messages::WindowServer::SetSystemTheme& message)
+{
+    bool success = WindowManager::the().update_theme(message.theme_path(), message.theme_name());
+    return make<Messages::WindowServer::SetSystemThemeResponse>(success);
+}
+
+OwnPtr<Messages::WindowServer::GetSystemThemeResponse> ClientConnection::handle(const Messages::WindowServer::GetSystemTheme&)
+{
+    auto wm_config = Core::ConfigFile::open("/etc/WindowServer/WindowServer.ini");
+    auto name = wm_config->read_entry("Theme", "Name");
+    return make<Messages::WindowServer::GetSystemThemeResponse>(name);
+}
+
+void ClientConnection::boost()
+{
+    // FIXME: Re-enable this when we have a solution for boosting.
+#if 0
+    if (set_process_boost(client_pid(), 10) < 0)
+        perror("boost: set_process_boost");
+#endif
+}
+
+void ClientConnection::deboost()
+{
+    // FIXME: Re-enable this when we have a solution for boosting.
+#if 0
+    if (set_process_boost(client_pid(), 0) < 0)
+        perror("deboost: set_process_boost");
+#endif
+}
+
+OwnPtr<Messages::WindowServer::SetWindowBaseSizeAndSizeIncrementResponse> ClientConnection::handle(const Messages::WindowServer::SetWindowBaseSizeAndSizeIncrement& message)
+{
+    auto it = m_windows.find(message.window_id());
+    if (it == m_windows.end()) {
+        did_misbehave("SetWindowBaseSizeAndSizeIncrementResponse: Bad window ID");
+        return nullptr;
+    }
+
+    auto& window = *it->value;
+    window.set_base_size(message.base_size());
+    window.set_size_increment(message.size_increment());
+
+    return make<Messages::WindowServer::SetWindowBaseSizeAndSizeIncrementResponse>();
+}
+
+void ClientConnection::handle(const Messages::WindowServer::EnableDisplayLink&)
+{
+    if (m_has_display_link)
+        return;
+    m_has_display_link = true;
+    Compositor::the().increment_display_link_count({});
+}
+
+void ClientConnection::handle(const Messages::WindowServer::DisableDisplayLink&)
+{
+    if (!m_has_display_link)
+        return;
+    m_has_display_link = false;
+    Compositor::the().decrement_display_link_count({});
+}
+
+void ClientConnection::notify_display_link(Badge<Compositor>)
+{
+    if (!m_has_display_link)
+        return;
+
+    post_message(Messages::WindowClient::DisplayLinkNotification());
+}
+
+}

Services/WindowServer/ClientConnection.h

@@ -0,0 +1,148 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Badge.h>
+#include <AK/Function.h>
+#include <AK/HashMap.h>
+#include <AK/OwnPtr.h>
+#include <AK/WeakPtr.h>
+#include <LibCore/Object.h>
+#include <LibGfx/Bitmap.h>
+#include <LibIPC/ClientConnection.h>
+#include <WindowServer/Event.h>
+#include <WindowServer/WindowServerEndpoint.h>
+
+namespace WindowServer {
+
+class Compositor;
+class Window;
+class Menu;
+class MenuBar;
+
+class ClientConnection final
+    : public IPC::ClientConnection<WindowServerEndpoint>
+    , public WindowServerEndpoint {
+    C_OBJECT(ClientConnection)
+public:
+    ~ClientConnection() override;
+    virtual void die() override;
+
+    void boost();
+    void deboost();
+
+    static ClientConnection* from_client_id(int client_id);
+    static void for_each_client(Function<void(ClientConnection&)>);
+
+    MenuBar* app_menubar() { return m_app_menubar.ptr(); }
+
+    bool is_showing_modal_window() const;
+
+    void notify_about_new_screen_rect(const Gfx::Rect&);
+    void notify_about_clipboard_contents_changed();
+    void post_paint_message(Window&, bool ignore_occlusion = false);
+
+    Menu* find_menu_by_id(int menu_id)
+    {
+        auto menu = m_menus.get(menu_id);
+        if (!menu.has_value())
+            return nullptr;
+        return const_cast<Menu*>(menu.value().ptr());
+    }
+
+    void notify_display_link(Badge<Compositor>);
+
+private:
+    explicit ClientConnection(Core::LocalSocket&, int client_id);
+
+    void destroy_window(Window&, Vector<i32>& destroyed_window_ids);
+
+    virtual OwnPtr<Messages::WindowServer::GreetResponse> handle(const Messages::WindowServer::Greet&) override;
+    virtual OwnPtr<Messages::WindowServer::CreateMenubarResponse> handle(const Messages::WindowServer::CreateMenubar&) override;
+    virtual OwnPtr<Messages::WindowServer::DestroyMenubarResponse> handle(const Messages::WindowServer::DestroyMenubar&) override;
+    virtual OwnPtr<Messages::WindowServer::CreateMenuResponse> handle(const Messages::WindowServer::CreateMenu&) override;
+    virtual OwnPtr<Messages::WindowServer::DestroyMenuResponse> handle(const Messages::WindowServer::DestroyMenu&) override;
+    virtual OwnPtr<Messages::WindowServer::AddMenuToMenubarResponse> handle(const Messages::WindowServer::AddMenuToMenubar&) override;
+    virtual OwnPtr<Messages::WindowServer::SetApplicationMenubarResponse> handle(const Messages::WindowServer::SetApplicationMenubar&) override;
+    virtual OwnPtr<Messages::WindowServer::AddMenuItemResponse> handle(const Messages::WindowServer::AddMenuItem&) override;
+    virtual OwnPtr<Messages::WindowServer::AddMenuSeparatorResponse> handle(const Messages::WindowServer::AddMenuSeparator&) override;
+    virtual OwnPtr<Messages::WindowServer::UpdateMenuItemResponse> handle(const Messages::WindowServer::UpdateMenuItem&) override;
+    virtual OwnPtr<Messages::WindowServer::CreateWindowResponse> handle(const Messages::WindowServer::CreateWindow&) override;
+    virtual OwnPtr<Messages::WindowServer::DestroyWindowResponse> handle(const Messages::WindowServer::DestroyWindow&) override;
+    virtual OwnPtr<Messages::WindowServer::SetWindowTitleResponse> handle(const Messages::WindowServer::SetWindowTitle&) override;
+    virtual OwnPtr<Messages::WindowServer::GetWindowTitleResponse> handle(const Messages::WindowServer::GetWindowTitle&) override;
+    virtual OwnPtr<Messages::WindowServer::SetWindowRectResponse> handle(const Messages::WindowServer::SetWindowRect&) override;
+    virtual OwnPtr<Messages::WindowServer::GetWindowRectResponse> handle(const Messages::WindowServer::GetWindowRect&) override;
+    virtual void handle(const Messages::WindowServer::InvalidateRect&) override;
+    virtual void handle(const Messages::WindowServer::DidFinishPainting&) override;
+    virtual OwnPtr<Messages::WindowServer::SetGlobalCursorTrackingResponse> handle(const Messages::WindowServer::SetGlobalCursorTracking&) override;
+    virtual OwnPtr<Messages::WindowServer::SetWindowOpacityResponse> handle(const Messages::WindowServer::SetWindowOpacity&) override;
+    virtual OwnPtr<Messages::WindowServer::SetWindowBackingStoreResponse> handle(const Messages::WindowServer::SetWindowBackingStore&) override;
+    virtual OwnPtr<Messages::WindowServer::GetClipboardContentsResponse> handle(const Messages::WindowServer::GetClipboardContents&) override;
+    virtual OwnPtr<Messages::WindowServer::SetClipboardContentsResponse> handle(const Messages::WindowServer::SetClipboardContents&) override;
+    virtual void handle(const Messages::WindowServer::WM_SetActiveWindow&) override;
+    virtual void handle(const Messages::WindowServer::WM_SetWindowMinimized&) override;
+    virtual void handle(const Messages::WindowServer::WM_StartWindowResize&) override;
+    virtual void handle(const Messages::WindowServer::WM_PopupWindowMenu&) override;
+    virtual OwnPtr<Messages::WindowServer::SetWindowHasAlphaChannelResponse> handle(const Messages::WindowServer::SetWindowHasAlphaChannel&) override;
+    virtual OwnPtr<Messages::WindowServer::MoveWindowToFrontResponse> handle(const Messages::WindowServer::MoveWindowToFront&) override;
+    virtual OwnPtr<Messages::WindowServer::SetFullscreenResponse> handle(const Messages::WindowServer::SetFullscreen&) override;
+    virtual void handle(const Messages::WindowServer::AsyncSetWallpaper&) override;
+    virtual OwnPtr<Messages::WindowServer::SetBackgroundColorResponse> handle(const Messages::WindowServer::SetBackgroundColor&) override;
+    virtual OwnPtr<Messages::WindowServer::SetWallpaperModeResponse> handle(const Messages::WindowServer::SetWallpaperMode&) override;
+    virtual OwnPtr<Messages::WindowServer::GetWallpaperResponse> handle(const Messages::WindowServer::GetWallpaper&) override;
+    virtual OwnPtr<Messages::WindowServer::SetResolutionResponse> handle(const Messages::WindowServer::SetResolution&) override;
+    virtual OwnPtr<Messages::WindowServer::SetWindowOverrideCursorResponse> handle(const Messages::WindowServer::SetWindowOverrideCursor&) override;
+    virtual OwnPtr<Messages::WindowServer::PopupMenuResponse> handle(const Messages::WindowServer::PopupMenu&) override;
+    virtual OwnPtr<Messages::WindowServer::DismissMenuResponse> handle(const Messages::WindowServer::DismissMenu&) override;
+    virtual OwnPtr<Messages::WindowServer::SetWindowIconBitmapResponse> handle(const Messages::WindowServer::SetWindowIconBitmap&) override;
+    virtual void handle(const Messages::WindowServer::WM_SetWindowTaskbarRect&) override;
+    virtual OwnPtr<Messages::WindowServer::StartDragResponse> handle(const Messages::WindowServer::StartDrag&) override;
+    virtual OwnPtr<Messages::WindowServer::SetSystemMenuResponse> handle(const Messages::WindowServer::SetSystemMenu&) override;
+    virtual OwnPtr<Messages::WindowServer::SetSystemThemeResponse> handle(const Messages::WindowServer::SetSystemTheme&) override;
+    virtual OwnPtr<Messages::WindowServer::GetSystemThemeResponse> handle(const Messages::WindowServer::GetSystemTheme&) override;
+    virtual OwnPtr<Messages::WindowServer::SetWindowBaseSizeAndSizeIncrementResponse> handle(const Messages::WindowServer::SetWindowBaseSizeAndSizeIncrement&) override;
+    virtual void handle(const Messages::WindowServer::EnableDisplayLink&) override;
+    virtual void handle(const Messages::WindowServer::DisableDisplayLink&) override;
+
+    Window* window_from_id(i32 window_id);
+
+    HashMap<int, NonnullRefPtr<Window>> m_windows;
+    HashMap<int, NonnullOwnPtr<MenuBar>> m_menubars;
+    HashMap<int, NonnullRefPtr<Menu>> m_menus;
+    WeakPtr<MenuBar> m_app_menubar;
+
+    int m_next_menubar_id { 10000 };
+    int m_next_menu_id { 20000 };
+    int m_next_window_id { 1982 };
+
+    bool m_has_display_link { false };
+
+    RefPtr<SharedBuffer> m_last_sent_clipboard_content;
+};
+
+}

Services/WindowServer/Clipboard.cpp

@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <WindowServer/Clipboard.h>
+
+namespace WindowServer {
+
+Clipboard& Clipboard::the()
+{
+    static Clipboard* s_the;
+    if (!s_the)
+        s_the = new Clipboard;
+    return *s_the;
+}
+
+Clipboard::Clipboard()
+{
+}
+
+Clipboard::~Clipboard()
+{
+}
+
+const u8* Clipboard::data() const
+{
+    if (!m_shared_buffer)
+        return nullptr;
+    return (const u8*)m_shared_buffer->data();
+}
+
+int Clipboard::size() const
+{
+    if (!m_shared_buffer)
+        return 0;
+    return m_contents_size;
+}
+
+void Clipboard::clear()
+{
+    m_shared_buffer = nullptr;
+    m_contents_size = 0;
+}
+
+void Clipboard::set_data(NonnullRefPtr<SharedBuffer>&& data, int contents_size, const String& data_type)
+{
+    dbg() << "Clipboard::set_data <- [" << data_type << "] " << data->data() << " (" << contents_size << " bytes)";
+    m_shared_buffer = move(data);
+    m_contents_size = contents_size;
+    m_data_type = data_type;
+
+    if (on_content_change)
+        on_content_change();
+}
+
+}

Services/WindowServer/Clipboard.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/SharedBuffer.h>
+#include <AK/String.h>
+
+namespace WindowServer {
+
+class Clipboard {
+public:
+    static Clipboard& the();
+    ~Clipboard();
+
+    bool has_data() const
+    {
+        return m_shared_buffer;
+    }
+
+    const String& data_type() const { return m_data_type; }
+    const u8* data() const;
+    int size() const;
+
+    void clear();
+    void set_data(NonnullRefPtr<SharedBuffer>&&, int contents_size, const String& data_type);
+
+    Function<void()> on_content_change;
+
+private:
+    Clipboard();
+
+    String m_data_type;
+    RefPtr<SharedBuffer> m_shared_buffer;
+    int m_contents_size { 0 };
+};
+
+}

Services/WindowServer/Compositor.cpp

@@ -0,0 +1,507 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Compositor.h"
+#include "ClientConnection.h"
+#include "Event.h"
+#include "EventLoop.h"
+#include "Screen.h"
+#include "Window.h"
+#include "WindowManager.h"
+#include <AK/Memory.h>
+#include <LibCore/Timer.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/Painter.h>
+#include <LibThread/BackgroundAction.h>
+
+namespace WindowServer {
+
+Compositor& Compositor::the()
+{
+    static Compositor s_the;
+    return s_the;
+}
+
+WallpaperMode mode_to_enum(const String& name)
+{
+    if (name == "simple")
+        return WallpaperMode::Simple;
+    if (name == "tile")
+        return WallpaperMode::Tile;
+    if (name == "center")
+        return WallpaperMode::Center;
+    if (name == "scaled")
+        return WallpaperMode::Scaled;
+    return WallpaperMode::Simple;
+}
+
+Compositor::Compositor()
+{
+    m_display_link_notify_timer = add<Core::Timer>(
+        1000 / 60, [this] {
+            notify_display_links();
+        });
+    m_display_link_notify_timer->stop();
+
+    m_compose_timer = Core::Timer::create_single_shot(
+        1000 / 60,
+        [this] {
+            compose();
+        },
+        this);
+
+    m_immediate_compose_timer = Core::Timer::create_single_shot(
+        0,
+        [this] {
+            compose();
+        },
+        this);
+
+    m_screen_can_set_buffer = Screen::the().can_set_buffer();
+    init_bitmaps();
+}
+
+void Compositor::init_bitmaps()
+{
+    auto& screen = Screen::the();
+    auto size = screen.size();
+
+    m_front_bitmap = Gfx::Bitmap::create_wrapper(Gfx::BitmapFormat::RGB32, size, screen.pitch(), screen.scanline(0));
+
+    if (m_screen_can_set_buffer)
+        m_back_bitmap = Gfx::Bitmap::create_wrapper(Gfx::BitmapFormat::RGB32, size, screen.pitch(), screen.scanline(size.height()));
+    else
+        m_back_bitmap = Gfx::Bitmap::create(Gfx::BitmapFormat::RGB32, size);
+
+    m_front_painter = make<Gfx::Painter>(*m_front_bitmap);
+    m_back_painter = make<Gfx::Painter>(*m_back_bitmap);
+
+    m_buffers_are_flipped = false;
+
+    invalidate();
+}
+
+void Compositor::compose()
+{
+    auto& wm = WindowManager::the();
+    if (m_wallpaper_mode == WallpaperMode::Unchecked)
+        m_wallpaper_mode = mode_to_enum(wm.wm_config()->read_entry("Background", "Mode", "simple"));
+    auto& ws = Screen::the();
+
+    auto dirty_rects = move(m_dirty_rects);
+
+    if (dirty_rects.size() == 0) {
+        // nothing dirtied since the last compose pass.
+        return;
+    }
+
+    dirty_rects.add(Gfx::Rect::intersection(m_last_geometry_label_rect, Screen::the().rect()));
+    dirty_rects.add(Gfx::Rect::intersection(m_last_cursor_rect, Screen::the().rect()));
+    dirty_rects.add(Gfx::Rect::intersection(m_last_dnd_rect, Screen::the().rect()));
+    dirty_rects.add(Gfx::Rect::intersection(current_cursor_rect(), Screen::the().rect()));
+
+    auto any_dirty_rect_intersects_window = [&dirty_rects](const Window& window) {
+        auto window_frame_rect = window.frame().rect();
+        for (auto& dirty_rect : dirty_rects.rects()) {
+            if (dirty_rect.intersects(window_frame_rect))
+                return true;
+        }
+        return false;
+    };
+
+    Color background_color = wm.palette().desktop_background();
+    String background_color_entry = wm.wm_config()->read_entry("Background", "Color", "");
+    if (!background_color_entry.is_empty()) {
+        background_color = Color::from_string(background_color_entry).value_or(background_color);
+    }
+
+    // Paint the wallpaper.
+    for (auto& dirty_rect : dirty_rects.rects()) {
+        if (wm.any_opaque_window_contains_rect(dirty_rect))
+            continue;
+        // FIXME: If the wallpaper is opaque, no need to fill with color!
+        m_back_painter->fill_rect(dirty_rect, background_color);
+        if (m_wallpaper) {
+            if (m_wallpaper_mode == WallpaperMode::Simple) {
+                m_back_painter->blit(dirty_rect.location(), *m_wallpaper, dirty_rect);
+            } else if (m_wallpaper_mode == WallpaperMode::Center) {
+                Gfx::Point offset { ws.size().width() / 2 - m_wallpaper->size().width() / 2,
+                    ws.size().height() / 2 - m_wallpaper->size().height() / 2 };
+                m_back_painter->blit_offset(dirty_rect.location(), *m_wallpaper,
+                    dirty_rect, offset);
+            } else if (m_wallpaper_mode == WallpaperMode::Tile) {
+                m_back_painter->draw_tiled_bitmap(dirty_rect, *m_wallpaper);
+            } else if (m_wallpaper_mode == WallpaperMode::Scaled) {
+                float hscale = (float)m_wallpaper->size().width() / (float)ws.size().width();
+                float vscale = (float)m_wallpaper->size().height() / (float)ws.size().height();
+
+                m_back_painter->blit_scaled(dirty_rect, *m_wallpaper, dirty_rect, hscale, vscale);
+            } else {
+                ASSERT_NOT_REACHED();
+            }
+        }
+    }
+
+    auto compose_window = [&](Window& window) -> IterationDecision {
+        if (!any_dirty_rect_intersects_window(window))
+            return IterationDecision::Continue;
+        Gfx::PainterStateSaver saver(*m_back_painter);
+        m_back_painter->add_clip_rect(window.frame().rect());
+        RefPtr<Gfx::Bitmap> backing_store = window.backing_store();
+        for (auto& dirty_rect : dirty_rects.rects()) {
+            if (wm.any_opaque_window_above_this_one_contains_rect(window, dirty_rect))
+                continue;
+            Gfx::PainterStateSaver saver(*m_back_painter);
+            m_back_painter->add_clip_rect(dirty_rect);
+            if (!backing_store)
+                m_back_painter->fill_rect(dirty_rect, wm.palette().window());
+            if (!window.is_fullscreen())
+                window.frame().paint(*m_back_painter);
+            if (!backing_store)
+                continue;
+
+            // Decide where we would paint this window's backing store.
+            // This is subtly different from widow.rect(), because window
+            // size may be different from its backing store size. This
+            // happens when the window has been resized and the client
+            // has not yet attached a new backing store. In this case,
+            // we want to try to blit the backing store at the same place
+            // it was previously, and fill the rest of the window with its
+            // background color.
+            Gfx::Rect backing_rect;
+            backing_rect.set_size(backing_store->size());
+            switch (WindowManager::the().resize_direction_of_window(window)) {
+            case ResizeDirection::None:
+            case ResizeDirection::Right:
+            case ResizeDirection::Down:
+            case ResizeDirection::DownRight:
+                backing_rect.set_location(window.rect().location());
+                break;
+            case ResizeDirection::Left:
+            case ResizeDirection::Up:
+            case ResizeDirection::UpLeft:
+                backing_rect.set_right_without_resize(window.rect().right());
+                backing_rect.set_bottom_without_resize(window.rect().bottom());
+                break;
+            case ResizeDirection::UpRight:
+                backing_rect.set_left(window.rect().left());
+                backing_rect.set_bottom_without_resize(window.rect().bottom());
+                break;
+            case ResizeDirection::DownLeft:
+                backing_rect.set_right_without_resize(window.rect().right());
+                backing_rect.set_top(window.rect().top());
+                break;
+            }
+
+            Gfx::Rect dirty_rect_in_backing_coordinates = dirty_rect
+                                                              .intersected(window.rect())
+                                                              .intersected(backing_rect)
+                                                              .translated(-backing_rect.location());
+
+            if (dirty_rect_in_backing_coordinates.is_empty())
+                continue;
+            auto dst = backing_rect.location().translated(dirty_rect_in_backing_coordinates.location());
+
+            m_back_painter->blit(dst, *backing_store, dirty_rect_in_backing_coordinates, window.opacity());
+            for (auto background_rect : window.rect().shatter(backing_rect))
+                m_back_painter->fill_rect(background_rect, wm.palette().window());
+        }
+        return IterationDecision::Continue;
+    };
+
+    // Paint the window stack.
+    if (auto* fullscreen_window = wm.active_fullscreen_window()) {
+        compose_window(*fullscreen_window);
+    } else {
+        wm.for_each_visible_window_from_back_to_front([&](Window& window) {
+            return compose_window(window);
+        });
+
+        draw_geometry_label();
+    }
+
+    run_animations();
+
+    draw_cursor();
+
+    if (m_flash_flush) {
+        for (auto& rect : dirty_rects.rects())
+            m_front_painter->fill_rect(rect, Color::Yellow);
+    }
+
+    if (m_screen_can_set_buffer)
+        flip_buffers();
+
+    for (auto& r : dirty_rects.rects())
+        flush(r);
+}
+
+void Compositor::flush(const Gfx::Rect& a_rect)
+{
+    auto rect = Gfx::Rect::intersection(a_rect, Screen::the().rect());
+
+    Gfx::RGBA32* front_ptr = m_front_bitmap->scanline(rect.y()) + rect.x();
+    Gfx::RGBA32* back_ptr = m_back_bitmap->scanline(rect.y()) + rect.x();
+    size_t pitch = m_back_bitmap->pitch();
+
+    // NOTE: The meaning of a flush depends on whether we can flip buffers or not.
+    //
+    //       If flipping is supported, flushing means that we've flipped, and now we
+    //       copy the changed bits from the front buffer to the back buffer, to keep
+    //       them in sync.
+    //
+    //       If flipping is not supported, flushing means that we copy the changed
+    //       rects from the backing bitmap to the display framebuffer.
+
+    Gfx::RGBA32* to_ptr;
+    const Gfx::RGBA32* from_ptr;
+
+    if (m_screen_can_set_buffer) {
+        to_ptr = back_ptr;
+        from_ptr = front_ptr;
+    } else {
+        to_ptr = front_ptr;
+        from_ptr = back_ptr;
+    }
+
+    for (int y = 0; y < rect.height(); ++y) {
+        fast_u32_copy(to_ptr, from_ptr, rect.width());
+        from_ptr = (const Gfx::RGBA32*)((const u8*)from_ptr + pitch);
+        to_ptr = (Gfx::RGBA32*)((u8*)to_ptr + pitch);
+    }
+}
+
+void Compositor::invalidate()
+{
+    m_dirty_rects.clear_with_capacity();
+    invalidate(Screen::the().rect());
+}
+
+void Compositor::invalidate(const Gfx::Rect& a_rect)
+{
+    auto rect = Gfx::Rect::intersection(a_rect, Screen::the().rect());
+    if (rect.is_empty())
+        return;
+
+    m_dirty_rects.add(rect);
+
+    // We delay composition by a timer interval, but to not affect latency too
+    // much, if a pending compose is not already scheduled, we also schedule an
+    // immediate compose the next spin of the event loop.
+    if (!m_compose_timer->is_active()) {
+        m_compose_timer->start();
+        m_immediate_compose_timer->start();
+    }
+}
+
+bool Compositor::set_background_color(const String& background_color)
+{
+    auto& wm = WindowManager::the();
+    wm.wm_config()->write_entry("Background", "Color", background_color);
+    bool ret_val = wm.wm_config()->sync();
+
+    if (ret_val)
+        Compositor::invalidate();
+
+    return ret_val;
+}
+
+bool Compositor::set_wallpaper_mode(const String& mode)
+{
+    auto& wm = WindowManager::the();
+    wm.wm_config()->write_entry("Background", "Mode", mode);
+    bool ret_val = wm.wm_config()->sync();
+
+    if (ret_val) {
+        m_wallpaper_mode = mode_to_enum(mode);
+        Compositor::invalidate();
+    }
+
+    return ret_val;
+}
+
+bool Compositor::set_wallpaper(const String& path, Function<void(bool)>&& callback)
+{
+    LibThread::BackgroundAction<RefPtr<Gfx::Bitmap>>::create(
+        [path] {
+            return Gfx::Bitmap::load_from_file(path);
+        },
+
+        [this, path, callback = move(callback)](RefPtr<Gfx::Bitmap> bitmap) {
+            m_wallpaper_path = path;
+            m_wallpaper = move(bitmap);
+            invalidate();
+            callback(true);
+        });
+    return true;
+}
+
+void Compositor::flip_buffers()
+{
+    ASSERT(m_screen_can_set_buffer);
+    swap(m_front_bitmap, m_back_bitmap);
+    swap(m_front_painter, m_back_painter);
+    Screen::the().set_buffer(m_buffers_are_flipped ? 0 : 1);
+    m_buffers_are_flipped = !m_buffers_are_flipped;
+}
+
+void Compositor::run_animations()
+{
+    static const int minimize_animation_steps = 10;
+
+    WindowManager::the().for_each_window([&](Window& window) {
+        if (window.in_minimize_animation()) {
+            int animation_index = window.minimize_animation_index();
+
+            auto from_rect = window.is_minimized() ? window.frame().rect() : window.taskbar_rect();
+            auto to_rect = window.is_minimized() ? window.taskbar_rect() : window.frame().rect();
+
+            float x_delta_per_step = (float)(from_rect.x() - to_rect.x()) / minimize_animation_steps;
+            float y_delta_per_step = (float)(from_rect.y() - to_rect.y()) / minimize_animation_steps;
+            float width_delta_per_step = (float)(from_rect.width() - to_rect.width()) / minimize_animation_steps;
+            float height_delta_per_step = (float)(from_rect.height() - to_rect.height()) / minimize_animation_steps;
+
+            Gfx::Rect rect {
+                from_rect.x() - (int)(x_delta_per_step * animation_index),
+                from_rect.y() - (int)(y_delta_per_step * animation_index),
+                from_rect.width() - (int)(width_delta_per_step * animation_index),
+                from_rect.height() - (int)(height_delta_per_step * animation_index)
+            };
+
+#ifdef MINIMIZE_ANIMATION_DEBUG
+            dbg() << "Minimize animation from " << from_rect << " to " << to_rect << " frame# " << animation_index << " " << rect;
+#endif
+
+            m_back_painter->draw_rect(rect, Color::White);
+
+            window.step_minimize_animation();
+            if (window.minimize_animation_index() >= minimize_animation_steps)
+                window.end_minimize_animation();
+
+            invalidate(rect);
+        }
+        return IterationDecision::Continue;
+    });
+}
+
+bool Compositor::set_resolution(int desired_width, int desired_height)
+{
+    auto screen_rect = Screen::the().rect();
+    if (screen_rect.width() == desired_width && screen_rect.height() == desired_height)
+        return true;
+
+    // Make sure it's impossible to set an invalid resolution
+    ASSERT(desired_width >= 640 && desired_height >= 480);
+    bool success = Screen::the().set_resolution(desired_width, desired_height);
+    init_bitmaps();
+    compose();
+    return success;
+}
+
+Gfx::Rect Compositor::current_cursor_rect() const
+{
+    auto& wm = WindowManager::the();
+    return { Screen::the().cursor_location().translated(-wm.active_cursor().hotspot()), wm.active_cursor().size() };
+}
+
+void Compositor::invalidate_cursor()
+{
+    auto& wm = WindowManager::the();
+    if (wm.dnd_client())
+        invalidate(wm.dnd_rect());
+    invalidate(current_cursor_rect());
+}
+
+void Compositor::draw_geometry_label()
+{
+    auto& wm = WindowManager::the();
+    auto* window_being_moved_or_resized = wm.m_move_window ? wm.m_move_window.ptr() : (wm.m_resize_window ? wm.m_resize_window.ptr() : nullptr);
+    if (!window_being_moved_or_resized) {
+        m_last_geometry_label_rect = {};
+        return;
+    }
+    auto geometry_string = window_being_moved_or_resized->rect().to_string();
+    if (!window_being_moved_or_resized->size_increment().is_null()) {
+        int width_steps = (window_being_moved_or_resized->width() - window_being_moved_or_resized->base_size().width()) / window_being_moved_or_resized->size_increment().width();
+        int height_steps = (window_being_moved_or_resized->height() - window_being_moved_or_resized->base_size().height()) / window_being_moved_or_resized->size_increment().height();
+        geometry_string = String::format("%s (%dx%d)", geometry_string.characters(), width_steps, height_steps);
+    }
+    auto geometry_label_rect = Gfx::Rect { 0, 0, wm.font().width(geometry_string) + 16, wm.font().glyph_height() + 10 };
+    geometry_label_rect.center_within(window_being_moved_or_resized->rect());
+    m_back_painter->fill_rect(geometry_label_rect, wm.palette().window());
+    m_back_painter->draw_rect(geometry_label_rect, wm.palette().threed_shadow2());
+    m_back_painter->draw_text(geometry_label_rect, geometry_string, Gfx::TextAlignment::Center, wm.palette().window_text());
+    m_last_geometry_label_rect = geometry_label_rect;
+}
+
+void Compositor::draw_cursor()
+{
+    auto& wm = WindowManager::the();
+    Gfx::Rect cursor_rect = current_cursor_rect();
+    m_back_painter->blit(cursor_rect.location(), wm.active_cursor().bitmap(), wm.active_cursor().rect());
+
+    if (wm.dnd_client()) {
+        auto dnd_rect = wm.dnd_rect();
+        m_back_painter->fill_rect(dnd_rect, wm.palette().selection().with_alpha(200));
+        if (!wm.dnd_text().is_empty()) {
+            auto text_rect = dnd_rect;
+            if (wm.dnd_bitmap())
+                text_rect.move_by(wm.dnd_bitmap()->width(), 0);
+            m_back_painter->draw_text(text_rect, wm.dnd_text(), Gfx::TextAlignment::CenterLeft, wm.palette().selection_text());
+        }
+        if (wm.dnd_bitmap()) {
+            m_back_painter->blit(dnd_rect.top_left(), *wm.dnd_bitmap(), wm.dnd_bitmap()->rect());
+        }
+        m_last_dnd_rect = dnd_rect;
+    } else {
+        m_last_dnd_rect = {};
+    }
+    m_last_cursor_rect = cursor_rect;
+}
+
+void Compositor::notify_display_links()
+{
+    ClientConnection::for_each_client([](auto& client) {
+        client.notify_display_link({});
+    });
+}
+
+void Compositor::increment_display_link_count(Badge<ClientConnection>)
+{
+    ++m_display_link_count;
+    if (m_display_link_count == 1)
+        m_display_link_notify_timer->start();
+}
+
+void Compositor::decrement_display_link_count(Badge<ClientConnection>)
+{
+    ASSERT(m_display_link_count);
+    --m_display_link_count;
+    if (!m_display_link_count)
+        m_display_link_notify_timer->stop();
+}
+
+}

Services/WindowServer/Compositor.h

@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/OwnPtr.h>
+#include <AK/RefPtr.h>
+#include <LibCore/Object.h>
+#include <LibGfx/DisjointRectSet.h>
+#include <LibGfx/Forward.h>
+
+namespace WindowServer {
+
+class ClientConnection;
+class Cursor;
+
+enum class WallpaperMode {
+    Simple,
+    Tile,
+    Center,
+    Scaled,
+    Unchecked
+};
+
+class Compositor final : public Core::Object {
+    C_OBJECT(Compositor)
+public:
+    static Compositor& the();
+
+    void compose();
+    void invalidate();
+    void invalidate(const Gfx::Rect&);
+
+    bool set_resolution(int desired_width, int desired_height);
+
+    bool set_background_color(const String& background_color);
+
+    bool set_wallpaper_mode(const String& mode);
+
+    bool set_wallpaper(const String& path, Function<void(bool)>&& callback);
+    String wallpaper_path() const { return m_wallpaper_path; }
+
+    void invalidate_cursor();
+    Gfx::Rect current_cursor_rect() const;
+
+    void increment_display_link_count(Badge<ClientConnection>);
+    void decrement_display_link_count(Badge<ClientConnection>);
+
+private:
+    Compositor();
+    void init_bitmaps();
+    void flip_buffers();
+    void flush(const Gfx::Rect&);
+    void draw_cursor();
+    void draw_geometry_label();
+    void draw_menubar();
+    void run_animations();
+    void notify_display_links();
+
+    RefPtr<Core::Timer> m_compose_timer;
+    RefPtr<Core::Timer> m_immediate_compose_timer;
+    bool m_flash_flush { false };
+    bool m_buffers_are_flipped { false };
+    bool m_screen_can_set_buffer { false };
+
+    RefPtr<Gfx::Bitmap> m_front_bitmap;
+    RefPtr<Gfx::Bitmap> m_back_bitmap;
+    OwnPtr<Gfx::Painter> m_back_painter;
+    OwnPtr<Gfx::Painter> m_front_painter;
+
+    Gfx::DisjointRectSet m_dirty_rects;
+
+    Gfx::Rect m_last_cursor_rect;
+    Gfx::Rect m_last_dnd_rect;
+    Gfx::Rect m_last_geometry_label_rect;
+
+    String m_wallpaper_path;
+    WallpaperMode m_wallpaper_mode { WallpaperMode::Unchecked };
+    RefPtr<Gfx::Bitmap> m_wallpaper;
+
+    RefPtr<Core::Timer> m_display_link_notify_timer;
+    size_t m_display_link_count { 0 };
+};
+
+}

Services/WindowServer/Cursor.cpp

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <WindowServer/Cursor.h>
+#include <WindowServer/WindowManager.h>
+
+namespace WindowServer {
+
+Cursor::Cursor(NonnullRefPtr<Gfx::Bitmap>&& bitmap, const Gfx::Point& hotspot)
+    : m_bitmap(move(bitmap))
+    , m_hotspot(hotspot)
+{
+}
+
+Cursor::~Cursor()
+{
+}
+
+NonnullRefPtr<Cursor> Cursor::create(NonnullRefPtr<Gfx::Bitmap>&& bitmap)
+{
+    return adopt(*new Cursor(move(bitmap), bitmap->rect().center()));
+}
+
+NonnullRefPtr<Cursor> Cursor::create(NonnullRefPtr<Gfx::Bitmap>&& bitmap, const Gfx::Point& hotspot)
+{
+    return adopt(*new Cursor(move(bitmap), hotspot));
+}
+
+RefPtr<Cursor> Cursor::create(StandardCursor standard_cursor)
+{
+    switch (standard_cursor) {
+    case StandardCursor::None:
+        return nullptr;
+    case StandardCursor::Arrow:
+        return WindowManager::the().arrow_cursor();
+    case StandardCursor::IBeam:
+        return WindowManager::the().i_beam_cursor();
+    case StandardCursor::ResizeHorizontal:
+        return WindowManager::the().resize_horizontally_cursor();
+    case StandardCursor::ResizeVertical:
+        return WindowManager::the().resize_vertically_cursor();
+    case StandardCursor::ResizeDiagonalTLBR:
+        return WindowManager::the().resize_diagonally_tlbr_cursor();
+    case StandardCursor::ResizeDiagonalBLTR:
+        return WindowManager::the().resize_diagonally_bltr_cursor();
+    case StandardCursor::Hand:
+        return WindowManager::the().hand_cursor();
+    case StandardCursor::Drag:
+        return WindowManager::the().drag_cursor();
+    }
+    ASSERT_NOT_REACHED();
+}
+
+}

Services/WindowServer/Cursor.h

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibGfx/Bitmap.h>
+
+namespace WindowServer {
+
+enum class StandardCursor {
+    None = 0,
+    Arrow,
+    IBeam,
+    ResizeHorizontal,
+    ResizeVertical,
+    ResizeDiagonalTLBR,
+    ResizeDiagonalBLTR,
+    Hand,
+    Drag,
+};
+
+class Cursor : public RefCounted<Cursor> {
+public:
+    static NonnullRefPtr<Cursor> create(NonnullRefPtr<Gfx::Bitmap>&&, const Gfx::Point& hotspot);
+    static NonnullRefPtr<Cursor> create(NonnullRefPtr<Gfx::Bitmap>&&);
+    static RefPtr<Cursor> create(StandardCursor);
+    ~Cursor();
+
+    Gfx::Point hotspot() const { return m_hotspot; }
+    const Gfx::Bitmap& bitmap() const { return *m_bitmap; }
+
+    Gfx::Rect rect() const { return m_bitmap->rect(); }
+    Gfx::Size size() const { return m_bitmap->size(); }
+
+private:
+    Cursor(NonnullRefPtr<Gfx::Bitmap>&&, const Gfx::Point&);
+
+    RefPtr<Gfx::Bitmap> m_bitmap;
+    Gfx::Point m_hotspot;
+};
+
+}

Services/WindowServer/Event.h

@@ -0,0 +1,157 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <Kernel/KeyCode.h>
+#include <LibCore/Event.h>
+#include <LibGfx/Rect.h>
+#include <WindowServer/Cursor.h>
+#include <WindowServer/WindowType.h>
+
+namespace WindowServer {
+
+class Event : public Core::Event {
+public:
+    enum Type {
+        Invalid = 3000,
+        MouseMove,
+        MouseDown,
+        MouseDoubleClick,
+        MouseUp,
+        MouseWheel,
+        WindowEntered,
+        WindowLeft,
+        KeyDown,
+        KeyUp,
+        WindowActivated,
+        WindowDeactivated,
+        WindowCloseRequest,
+        WindowResized,
+    };
+
+    Event() {}
+    explicit Event(Type type)
+        : Core::Event(type)
+    {
+    }
+    virtual ~Event() {}
+
+    bool is_mouse_event() const { return type() == MouseMove || type() == MouseDown || type() == MouseDoubleClick || type() == MouseUp || type() == MouseWheel; }
+    bool is_key_event() const { return type() == KeyUp || type() == KeyDown; }
+};
+
+enum class MouseButton : u8 {
+    None = 0,
+    Left = 1,
+    Right = 2,
+    Middle = 4,
+    Back = 8,
+    Forward = 16,
+};
+
+class KeyEvent final : public Event {
+public:
+    KeyEvent(Type type, int key, char character, u8 modifiers)
+        : Event(type)
+        , m_key(key)
+        , m_character(character)
+        , m_modifiers(modifiers)
+    {
+    }
+
+    int key() const { return m_key; }
+    bool ctrl() const { return m_modifiers & Mod_Ctrl; }
+    bool alt() const { return m_modifiers & Mod_Alt; }
+    bool shift() const { return m_modifiers & Mod_Shift; }
+    bool logo() const { return m_modifiers & Mod_Logo; }
+    u8 modifiers() const { return m_modifiers; }
+    char character() const { return m_character; }
+
+private:
+    friend class EventLoop;
+    friend class Screen;
+    int m_key { 0 };
+    char m_character { 0 };
+    u8 m_modifiers { 0 };
+};
+
+class MouseEvent final : public Event {
+public:
+    MouseEvent(Type type, const Gfx::Point& position, unsigned buttons, MouseButton button, unsigned modifiers, int wheel_delta = 0)
+        : Event(type)
+        , m_position(position)
+        , m_buttons(buttons)
+        , m_button(button)
+        , m_modifiers(modifiers)
+        , m_wheel_delta(wheel_delta)
+    {
+    }
+
+    Gfx::Point position() const { return m_position; }
+    int x() const { return m_position.x(); }
+    int y() const { return m_position.y(); }
+    MouseButton button() const { return m_button; }
+    unsigned buttons() const { return m_buttons; }
+    unsigned modifiers() const { return m_modifiers; }
+    int wheel_delta() const { return m_wheel_delta; }
+    bool is_drag() const { return m_drag; }
+    const String& drag_data_type() const { return m_drag_data_type; }
+
+    void set_drag(bool b) { m_drag = b; }
+    void set_drag_data_type(const String& drag_data_type) { m_drag_data_type = drag_data_type; }
+
+    MouseEvent translated(const Gfx::Point& delta) const { return MouseEvent((Type)type(), m_position.translated(delta), m_buttons, m_button, m_modifiers, m_wheel_delta); }
+
+private:
+    Gfx::Point m_position;
+    unsigned m_buttons { 0 };
+    MouseButton m_button { MouseButton::None };
+    unsigned m_modifiers { 0 };
+    int m_wheel_delta { 0 };
+    bool m_drag { false };
+    String m_drag_data_type;
+};
+
+class ResizeEvent final : public Event {
+public:
+    ResizeEvent(const Gfx::Rect& old_rect, const Gfx::Rect& rect)
+        : Event(Event::WindowResized)
+        , m_old_rect(old_rect)
+        , m_rect(rect)
+    {
+    }
+
+    Gfx::Rect old_rect() const { return m_old_rect; }
+    Gfx::Rect rect() const { return m_rect; }
+
+private:
+    Gfx::Rect m_old_rect;
+    Gfx::Rect m_rect;
+};
+
+}

Services/WindowServer/EventLoop.cpp

@@ -0,0 +1,157 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Clipboard.h"
+#include <Kernel/KeyCode.h>
+#include <Kernel/MousePacket.h>
+#include <LibCore/LocalSocket.h>
+#include <LibCore/Object.h>
+#include <WindowServer/ClientConnection.h>
+#include <WindowServer/Cursor.h>
+#include <WindowServer/Event.h>
+#include <WindowServer/EventLoop.h>
+#include <WindowServer/Screen.h>
+#include <WindowServer/WindowManager.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/select.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <time.h>
+#include <unistd.h>
+
+//#define WSMESSAGELOOP_DEBUG
+
+namespace WindowServer {
+
+EventLoop::EventLoop()
+    : m_server(Core::LocalServer::construct())
+{
+    m_keyboard_fd = open("/dev/keyboard", O_RDONLY | O_NONBLOCK | O_CLOEXEC);
+    m_mouse_fd = open("/dev/mouse", O_RDONLY | O_NONBLOCK | O_CLOEXEC);
+
+    bool ok = m_server->take_over_from_system_server();
+    ASSERT(ok);
+
+    m_server->on_ready_to_accept = [this] {
+        auto client_socket = m_server->accept();
+        if (!client_socket) {
+            dbg() << "WindowServer: accept failed.";
+            return;
+        }
+        static int s_next_client_id = 0;
+        int client_id = ++s_next_client_id;
+        IPC::new_client_connection<ClientConnection>(*client_socket, client_id);
+    };
+
+    ASSERT(m_keyboard_fd >= 0);
+    ASSERT(m_mouse_fd >= 0);
+
+    m_keyboard_notifier = Core::Notifier::construct(m_keyboard_fd, Core::Notifier::Read);
+    m_keyboard_notifier->on_ready_to_read = [this] { drain_keyboard(); };
+
+    m_mouse_notifier = Core::Notifier::construct(m_mouse_fd, Core::Notifier::Read);
+    m_mouse_notifier->on_ready_to_read = [this] { drain_mouse(); };
+
+    Clipboard::the().on_content_change = [&] {
+        ClientConnection::for_each_client([&](auto& client) {
+            client.notify_about_clipboard_contents_changed();
+        });
+    };
+}
+
+EventLoop::~EventLoop()
+{
+}
+
+void EventLoop::drain_mouse()
+{
+    auto& screen = Screen::the();
+    MousePacket state;
+    state.buttons = screen.mouse_button_state();
+    unsigned buttons = state.buttons;
+    MousePacket packets[32];
+
+    ssize_t nread = read(m_mouse_fd, &packets, sizeof(packets));
+    if (nread < 0) {
+        perror("EventLoop::drain_mouse read");
+        return;
+    }
+    size_t npackets = nread / sizeof(MousePacket);
+    if (!npackets)
+        return;
+    for (size_t i = 0; i < npackets; ++i) {
+        auto& packet = packets[i];
+#ifdef WSMESSAGELOOP_DEBUG
+        dbgprintf("EventLoop: Mouse X %d, Y %d, Z %d, relative %d\n", packet.x, packet.y, packet.z, packet.is_relative);
+#endif
+        buttons = packet.buttons;
+
+        state.is_relative = packet.is_relative;
+        if (packet.is_relative) {
+            state.x += packet.x;
+            state.y -= packet.y;
+            state.z += packet.z;
+        } else {
+            state.x = packet.x;
+            state.y = packet.y;
+            state.z += packet.z;
+        }
+
+        if (buttons != state.buttons) {
+            state.buttons = buttons;
+#ifdef WSMESSAGELOOP_DEBUG
+            dbgprintf("EventLoop: Mouse Button Event\n");
+#endif
+            screen.on_receive_mouse_data(state);
+            if (state.is_relative) {
+                state.x = 0;
+                state.y = 0;
+                state.z = 0;
+            }
+        }
+    }
+    if (state.is_relative && (state.x || state.y || state.z))
+        screen.on_receive_mouse_data(state);
+    if (!state.is_relative)
+        screen.on_receive_mouse_data(state);
+}
+
+void EventLoop::drain_keyboard()
+{
+    auto& screen = Screen::the();
+    for (;;) {
+        ::KeyEvent event;
+        ssize_t nread = read(m_keyboard_fd, (u8*)&event, sizeof(::KeyEvent));
+        if (nread == 0)
+            break;
+        ASSERT(nread == sizeof(::KeyEvent));
+        screen.on_receive_keyboard_data(event);
+    }
+}
+
+}

Services/WindowServer/EventLoop.h

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/LocalServer.h>
+#include <LibCore/Notifier.h>
+
+namespace WindowServer {
+
+class ClientConnection;
+
+class EventLoop {
+public:
+    EventLoop();
+    virtual ~EventLoop();
+
+    int exec() { return m_event_loop.exec(); }
+
+private:
+    void drain_mouse();
+    void drain_keyboard();
+
+    Core::EventLoop m_event_loop;
+    int m_keyboard_fd { -1 };
+    RefPtr<Core::Notifier> m_keyboard_notifier;
+    int m_mouse_fd { -1 };
+    RefPtr<Core::Notifier> m_mouse_notifier;
+    RefPtr<Core::LocalServer> m_server;
+};
+
+}

Services/WindowServer/Makefile

@@ -0,0 +1,38 @@
+OBJS = \
+    AppletManager.o \
+    Button.o \
+    ClientConnection.o \
+    Clipboard.o \
+    Compositor.o \
+    Cursor.o \
+    EventLoop.o \
+    Menu.o \
+    MenuBar.o \
+    MenuItem.o \
+    MenuManager.o \
+    Screen.o \
+    Window.o \
+    WindowFrame.o \
+    WindowManager.o \
+    WindowSwitcher.o \
+    main.o
+
+PROGRAM = WindowServer
+
+LIB_DEPS = Gfx Core Thread Pthread IPC
+
+*.cpp: WindowServerEndpoint.h WindowClientEndpoint.h
+
+WindowServerEndpoint.h: WindowServer.ipc | IPCCOMPILER
+	@echo "IPC $<"; $(IPCCOMPILER) $< > $@
+
+WindowClientEndpoint.h: WindowClient.ipc | IPCCOMPILER
+	@echo "IPC $<"; $(IPCCOMPILER) $< > $@
+
+EXTRA_CLEAN = WindowServerEndpoint.h WindowClientEndpoint.h
+
+install:
+	mkdir -p ../../Root/usr/include/WindowServer/
+	cp *.h ../../Root/usr/include/WindowServer/
+
+include ../../Makefile.common

Services/WindowServer/Menu.cpp

@@ -0,0 +1,570 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Shannon Booth <shannon.ml.booth@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Menu.h"
+#include "Event.h"
+#include "EventLoop.h"
+#include "MenuItem.h"
+#include "MenuManager.h"
+#include "Screen.h"
+#include "Window.h"
+#include "WindowManager.h"
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/CharacterBitmap.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/Painter.h>
+#include <LibGfx/StylePainter.h>
+#include <LibGfx/Triangle.h>
+#include <WindowServer/ClientConnection.h>
+#include <WindowServer/WindowClientEndpoint.h>
+
+namespace WindowServer {
+
+Menu::Menu(ClientConnection* client, int menu_id, const String& name)
+    : Core::Object(client)
+    , m_client(client)
+    , m_menu_id(menu_id)
+    , m_name(move(name))
+{
+}
+
+Menu::~Menu()
+{
+}
+
+void Menu::set_title_font(const Gfx::Font& font)
+{
+    m_title_font = &font;
+}
+
+const Gfx::Font& Menu::title_font() const
+{
+    return *m_title_font;
+}
+
+const Gfx::Font& Menu::font() const
+{
+    return Gfx::Font::default_font();
+}
+
+static const char* s_checked_bitmap_data = {
+    "         "
+    "       # "
+    "      ## "
+    "     ### "
+    " ## ###  "
+    " #####   "
+    "  ###    "
+    "   #     "
+    "         "
+};
+
+static const char* s_submenu_arrow_bitmap_data = {
+    "         "
+    "   #     "
+    "   ##    "
+    "   ###   "
+    "   ####  "
+    "   ###   "
+    "   ##    "
+    "   #     "
+    "         "
+};
+
+static Gfx::CharacterBitmap* s_checked_bitmap;
+static const int s_checked_bitmap_width = 9;
+static const int s_checked_bitmap_height = 9;
+static const int s_submenu_arrow_bitmap_width = 9;
+static const int s_submenu_arrow_bitmap_height = 9;
+static const int s_item_icon_width = 16;
+static const int s_stripe_width = 23;
+
+int Menu::content_width() const
+{
+    int widest_text = 0;
+    int widest_shortcut = 0;
+    for (auto& item : m_items) {
+        if (item.type() != MenuItem::Text)
+            continue;
+        int text_width = font().width(item.text());
+        if (!item.shortcut_text().is_empty()) {
+            int shortcut_width = font().width(item.shortcut_text());
+            widest_shortcut = max(shortcut_width, widest_shortcut);
+        }
+        widest_text = max(widest_text, text_width);
+    }
+
+    int widest_item = widest_text + s_stripe_width;
+    if (widest_shortcut)
+        widest_item += padding_between_text_and_shortcut() + widest_shortcut;
+
+    return max(widest_item, rect_in_menubar().width()) + horizontal_padding() + frame_thickness() * 2;
+}
+
+void Menu::redraw()
+{
+    if (!menu_window())
+        return;
+    draw();
+    menu_window()->invalidate();
+}
+
+Window& Menu::ensure_menu_window()
+{
+    if (m_menu_window)
+        return *m_menu_window;
+
+    int width = this->content_width();
+
+    Gfx::Point next_item_location(frame_thickness(), frame_thickness());
+    for (auto& item : m_items) {
+        int height = 0;
+        if (item.type() == MenuItem::Text)
+            height = item_height();
+        else if (item.type() == MenuItem::Separator)
+            height = 8;
+        item.set_rect({ next_item_location, { width - frame_thickness() * 2, height } });
+        next_item_location.move_by(0, height);
+    }
+
+    int window_height_available = Screen::the().height() - MenuManager::the().menubar_rect().height() - frame_thickness() * 2;
+    int max_window_height = (window_height_available / item_height()) * item_height() + frame_thickness() * 2;
+    int content_height = m_items.is_empty() ? 0 : (m_items.last().rect().bottom() + 1) + frame_thickness();
+    int window_height = min(max_window_height, content_height);
+    if (window_height < content_height) {
+        m_scrollable = true;
+        m_max_scroll_offset = item_count() - window_height / item_height() + 2;
+    }
+
+    auto window = Window::construct(*this, WindowType::Menu);
+    window->set_rect(0, 0, width, window_height);
+    m_menu_window = move(window);
+    draw();
+
+    return *m_menu_window;
+}
+
+int Menu::visible_item_count() const
+{
+    if (!is_scrollable())
+        return m_items.size();
+    ASSERT(m_menu_window);
+    // Make space for up/down arrow indicators
+    return m_menu_window->height() / item_height() - 2;
+}
+
+void Menu::draw()
+{
+    auto palette = WindowManager::the().palette();
+    m_theme_index_at_last_paint = MenuManager::the().theme_index();
+
+    ASSERT(menu_window());
+    ASSERT(menu_window()->backing_store());
+    Gfx::Painter painter(*menu_window()->backing_store());
+
+    Gfx::Rect rect { {}, menu_window()->size() };
+    Gfx::StylePainter::paint_window_frame(painter, rect, palette);
+    painter.fill_rect(rect.shrunken(6, 6), palette.menu_base());
+    int width = this->content_width();
+
+    if (!s_checked_bitmap)
+        s_checked_bitmap = &Gfx::CharacterBitmap::create_from_ascii(s_checked_bitmap_data, s_checked_bitmap_width, s_checked_bitmap_height).leak_ref();
+
+    bool has_checkable_items = false;
+    bool has_items_with_icon = false;
+    for (auto& item : m_items) {
+        has_checkable_items = has_checkable_items | item.is_checkable();
+        has_items_with_icon = has_items_with_icon | !!item.icon();
+    }
+
+    Gfx::Rect stripe_rect { frame_thickness(), frame_thickness(), s_stripe_width, menu_window()->height() - frame_thickness() * 2 };
+    painter.fill_rect(stripe_rect, palette.menu_stripe());
+    painter.draw_line(stripe_rect.top_right(), stripe_rect.bottom_right(), palette.menu_stripe().darkened());
+
+    int visible_item_count = this->visible_item_count();
+
+    if (is_scrollable()) {
+        bool can_go_up = m_scroll_offset > 0;
+        bool can_go_down = m_scroll_offset < m_max_scroll_offset;
+        Gfx::Rect up_indicator_rect { frame_thickness(), frame_thickness(), content_width(), item_height() };
+        painter.draw_text(up_indicator_rect, "\xc3\xb6", Gfx::TextAlignment::Center, can_go_up ? palette.menu_base_text() : palette.color(ColorRole::DisabledText));
+        Gfx::Rect down_indicator_rect { frame_thickness(), menu_window()->height() - item_height() - frame_thickness(), content_width(), item_height() };
+        painter.draw_text(down_indicator_rect, "\xc3\xb7", Gfx::TextAlignment::Center, can_go_down ? palette.menu_base_text() : palette.color(ColorRole::DisabledText));
+    }
+
+    for (int i = 0; i < visible_item_count; ++i) {
+        auto& item = m_items.at(m_scroll_offset + i);
+        if (item.type() == MenuItem::Text) {
+            Color text_color = palette.menu_base_text();
+            if (&item == hovered_item() && item.is_enabled()) {
+                painter.fill_rect(item.rect(), palette.menu_selection());
+                painter.draw_rect(item.rect(), palette.menu_selection().darkened());
+                text_color = palette.menu_selection_text();
+            } else if (!item.is_enabled()) {
+                text_color = Color::MidGray;
+            }
+            Gfx::Rect text_rect = item.rect().translated(stripe_rect.width() + 6, 0);
+            if (item.is_checkable()) {
+                if (item.is_exclusive()) {
+                    Gfx::Rect radio_rect { item.rect().x() + 5, 0, 12, 12 };
+                    radio_rect.center_vertically_within(text_rect);
+                    Gfx::StylePainter::paint_radio_button(painter, radio_rect, palette, item.is_checked(), false);
+                } else {
+                    Gfx::Rect checkmark_rect { item.rect().x() + 7, 0, s_checked_bitmap_width, s_checked_bitmap_height };
+                    checkmark_rect.center_vertically_within(text_rect);
+                    Gfx::Rect checkbox_rect = checkmark_rect.inflated(4, 4);
+                    painter.fill_rect(checkbox_rect, palette.base());
+                    Gfx::StylePainter::paint_frame(painter, checkbox_rect, palette, Gfx::FrameShape::Container, Gfx::FrameShadow::Sunken, 2);
+                    if (item.is_checked()) {
+                        painter.draw_bitmap(checkmark_rect.location(), *s_checked_bitmap, palette.button_text());
+                    }
+                }
+            } else if (item.icon()) {
+                Gfx::Rect icon_rect { item.rect().x() + 3, 0, s_item_icon_width, s_item_icon_width };
+                icon_rect.center_vertically_within(text_rect);
+                painter.blit(icon_rect.location(), *item.icon(), item.icon()->rect());
+            }
+            painter.draw_text(text_rect, item.text(), Gfx::TextAlignment::CenterLeft, text_color);
+            if (!item.shortcut_text().is_empty()) {
+                painter.draw_text(item.rect().translated(-right_padding(), 0), item.shortcut_text(), Gfx::TextAlignment::CenterRight, text_color);
+            }
+            if (item.is_submenu()) {
+                static auto& submenu_arrow_bitmap = Gfx::CharacterBitmap::create_from_ascii(s_submenu_arrow_bitmap_data, s_submenu_arrow_bitmap_width, s_submenu_arrow_bitmap_height).leak_ref();
+                Gfx::Rect submenu_arrow_rect {
+                    item.rect().right() - s_submenu_arrow_bitmap_width - 2,
+                    0,
+                    s_submenu_arrow_bitmap_width,
+                    s_submenu_arrow_bitmap_height
+                };
+                submenu_arrow_rect.center_vertically_within(item.rect());
+                painter.draw_bitmap(submenu_arrow_rect.location(), submenu_arrow_bitmap, text_color);
+            }
+        } else if (item.type() == MenuItem::Separator) {
+            Gfx::Point p1(item.rect().translated(stripe_rect.width() + 4, 0).x(), item.rect().center().y() - 1);
+            Gfx::Point p2(width - 7, item.rect().center().y() - 1);
+            painter.draw_line(p1, p2, palette.threed_shadow1());
+            painter.draw_line(p1.translated(0, 1), p2.translated(0, 1), palette.threed_highlight());
+        }
+    }
+}
+
+MenuItem* Menu::hovered_item() const
+{
+    if (m_hovered_item_index == -1)
+        return nullptr;
+    return const_cast<MenuItem*>(&item(m_hovered_item_index));
+}
+
+void Menu::update_for_new_hovered_item()
+{
+    if (hovered_item() && hovered_item()->is_submenu()) {
+        MenuManager::the().close_everyone_not_in_lineage(*hovered_item()->submenu());
+        hovered_item()->submenu()->popup(hovered_item()->rect().top_right().translated(menu_window()->rect().location()), true);
+    } else {
+        MenuManager::the().close_everyone_not_in_lineage(*this);
+        MenuManager::the().set_current_menu(this);
+        menu_window()->set_visible(true);
+    }
+    redraw();
+}
+
+void Menu::open_hovered_item()
+{
+    ASSERT(menu_window());
+    ASSERT(menu_window()->is_visible());
+    if (!hovered_item())
+        return;
+    if (hovered_item()->is_enabled())
+        did_activate(*hovered_item());
+    clear_hovered_item();
+}
+
+void Menu::descend_into_submenu_at_hovered_item()
+{
+    ASSERT(hovered_item());
+    ASSERT(hovered_item()->is_submenu());
+    auto submenu = hovered_item()->submenu();
+    submenu->m_hovered_item_index = 0;
+    ASSERT(submenu->hovered_item()->type() != MenuItem::Separator);
+    submenu->update_for_new_hovered_item();
+    m_in_submenu = true;
+}
+
+void Menu::handle_mouse_move_event(const MouseEvent& mouse_event)
+{
+    ASSERT(menu_window());
+    if (hovered_item() && hovered_item()->is_submenu()) {
+
+        auto item = *hovered_item();
+        auto submenu_top_left = item.rect().location() + Gfx::Point { item.rect().width(), 0 };
+        auto submenu_bottom_left = submenu_top_left + Gfx::Point { 0, item.submenu()->menu_window()->height() };
+
+        auto safe_hover_triangle = Gfx::Triangle { m_last_position_in_hover, submenu_top_left, submenu_bottom_left };
+        m_last_position_in_hover = mouse_event.position();
+
+        // Don't update the hovered item if mouse is moving towards a submenu
+        if (safe_hover_triangle.contains(mouse_event.position()))
+            return;
+    }
+
+    int index = item_index_at(mouse_event.position());
+    if (m_hovered_item_index == index)
+        return;
+    m_hovered_item_index = index;
+
+    // FIXME: Tell parent menu (if it exists) that it is currently in a submenu
+    m_in_submenu = false;
+    update_for_new_hovered_item();
+    return;
+}
+
+void Menu::event(Core::Event& event)
+{
+    if (event.type() == Event::MouseMove) {
+        handle_mouse_move_event(static_cast<const MouseEvent&>(event));
+        return;
+    }
+
+    if (event.type() == Event::MouseUp) {
+        open_hovered_item();
+        return;
+    }
+
+    if (event.type() == Event::MouseWheel && is_scrollable()) {
+        ASSERT(menu_window());
+        auto& mouse_event = static_cast<const MouseEvent&>(event);
+        m_scroll_offset += mouse_event.wheel_delta();
+        m_scroll_offset = clamp(m_scroll_offset, 0, m_max_scroll_offset);
+
+        int index = item_index_at(mouse_event.position());
+        if (m_hovered_item_index == index)
+            return;
+
+        m_hovered_item_index = index;
+        update_for_new_hovered_item();
+        return;
+    }
+
+    if (event.type() == Event::KeyDown) {
+        auto key = static_cast<KeyEvent&>(event).key();
+
+        if (!(key == Key_Up || key == Key_Down || key == Key_Left || key == Key_Right || key == Key_Return))
+            return;
+
+        ASSERT(menu_window());
+        ASSERT(menu_window()->is_visible());
+
+        // Default to the first item on key press if one has not been selected yet
+        if (!hovered_item()) {
+            m_hovered_item_index = 0;
+            update_for_new_hovered_item();
+            return;
+        }
+
+        // Pass the event for the submenu that we are currently in to handle
+        if (m_in_submenu && key != Key_Left) {
+            ASSERT(hovered_item()->is_submenu());
+            hovered_item()->submenu()->dispatch_event(event);
+            return;
+        }
+
+        if (key == Key_Return) {
+            if (!hovered_item()->is_enabled())
+                return;
+            if (hovered_item()->is_submenu())
+                descend_into_submenu_at_hovered_item();
+            else
+                open_hovered_item();
+            return;
+        }
+
+        if (key == Key_Up) {
+            ASSERT(m_items.at(0).type() != MenuItem::Separator);
+
+            if (is_scrollable() && m_hovered_item_index == 0)
+                return;
+
+            auto original_index = m_hovered_item_index;
+            do {
+                if (m_hovered_item_index == 0)
+                    m_hovered_item_index = m_items.size() - 1;
+                else
+                    --m_hovered_item_index;
+                if (m_hovered_item_index == original_index)
+                    return;
+            } while (hovered_item()->type() == MenuItem::Separator || !hovered_item()->is_enabled());
+
+            ASSERT(m_hovered_item_index >= 0 && m_hovered_item_index <= static_cast<int>(m_items.size()) - 1);
+
+            if (is_scrollable() && m_hovered_item_index < m_scroll_offset)
+                --m_scroll_offset;
+
+            update_for_new_hovered_item();
+            return;
+        }
+
+        if (key == Key_Down) {
+            ASSERT(m_items.at(0).type() != MenuItem::Separator);
+
+            if (is_scrollable() && m_hovered_item_index == static_cast<int>(m_items.size()) - 1)
+                return;
+
+            auto original_index = m_hovered_item_index;
+            do {
+                if (m_hovered_item_index == static_cast<int>(m_items.size()) - 1)
+                    m_hovered_item_index = 0;
+                else
+                    ++m_hovered_item_index;
+                if (m_hovered_item_index == original_index)
+                    return;
+            } while (hovered_item()->type() == MenuItem::Separator || !hovered_item()->is_enabled());
+
+            ASSERT(m_hovered_item_index >= 0 && m_hovered_item_index <= static_cast<int>(m_items.size()) - 1);
+
+            if (is_scrollable() && m_hovered_item_index >= (m_scroll_offset + visible_item_count()))
+                ++m_scroll_offset;
+
+            update_for_new_hovered_item();
+            return;
+        }
+
+        if (key == Key_Left) {
+            if (!m_in_submenu)
+                return;
+
+            ASSERT(hovered_item()->is_submenu());
+            hovered_item()->submenu()->clear_hovered_item();
+            m_in_submenu = false;
+            return;
+        }
+
+        if (key == Key_Right) {
+            if (hovered_item()->is_enabled() && hovered_item()->is_submenu())
+                descend_into_submenu_at_hovered_item();
+            return;
+        }
+    }
+    Core::Object::event(event);
+}
+
+void Menu::clear_hovered_item()
+{
+    if (!hovered_item())
+        return;
+    m_hovered_item_index = -1;
+    m_in_submenu = false;
+    redraw();
+}
+
+void Menu::did_activate(MenuItem& item)
+{
+    if (item.type() == MenuItem::Type::Separator)
+        return;
+
+    if (on_item_activation)
+        on_item_activation(item);
+
+    MenuManager::the().close_bar();
+
+    if (m_client)
+        m_client->post_message(Messages::WindowClient::MenuItemActivated(m_menu_id, item.identifier()));
+}
+
+MenuItem* Menu::item_with_identifier(unsigned identifer)
+{
+    for (auto& item : m_items) {
+        if (item.identifier() == identifer)
+            return &item;
+    }
+    return nullptr;
+}
+
+int Menu::item_index_at(const Gfx::Point& position)
+{
+    int i = 0;
+    for (auto& item : m_items) {
+        if (item.rect().contains(position))
+            return i;
+        ++i;
+    }
+    return -1;
+}
+
+void Menu::close()
+{
+    MenuManager::the().close_menu_and_descendants(*this);
+}
+
+void Menu::redraw_if_theme_changed()
+{
+    if (m_theme_index_at_last_paint != MenuManager::the().theme_index())
+        redraw();
+}
+
+void Menu::popup(const Gfx::Point& position, bool is_submenu)
+{
+    if (is_empty()) {
+        dbg() << "Menu: Empty menu popup";
+        return;
+    }
+
+    auto& window = ensure_menu_window();
+    redraw_if_theme_changed();
+
+    const int margin = 30;
+    Gfx::Point adjusted_pos = position;
+
+    if (adjusted_pos.x() + window.width() >= Screen::the().width() - margin) {
+        adjusted_pos = adjusted_pos.translated(-window.width(), 0);
+    }
+    if (adjusted_pos.y() + window.height() >= Screen::the().height() - margin) {
+        adjusted_pos = adjusted_pos.translated(0, -window.height());
+    }
+
+    if (adjusted_pos.y() < MenuManager::the().menubar_rect().height())
+        adjusted_pos.set_y(MenuManager::the().menubar_rect().height());
+
+    window.move_to(adjusted_pos);
+    window.set_visible(true);
+    MenuManager::the().set_current_menu(this, is_submenu);
+}
+
+bool Menu::is_menu_ancestor_of(const Menu& other) const
+{
+    for (auto& item : m_items) {
+        if (!item.is_submenu())
+            continue;
+        auto& submenu = *const_cast<MenuItem&>(item).submenu();
+        if (&submenu == &other)
+            return true;
+        if (submenu.is_menu_ancestor_of(other))
+            return true;
+    }
+    return false;
+}
+
+}

Services/WindowServer/Menu.h

@@ -0,0 +1,158 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/NonnullOwnPtrVector.h>
+#include <AK/String.h>
+#include <AK/WeakPtr.h>
+#include <LibCore/Object.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/Forward.h>
+#include <LibGfx/Rect.h>
+#include <WindowServer/Cursor.h>
+#include <WindowServer/MenuItem.h>
+#include <WindowServer/Window.h>
+
+namespace WindowServer {
+
+class ClientConnection;
+class MenuBar;
+class Event;
+
+class Menu final : public Core::Object {
+    C_OBJECT(Menu)
+public:
+    Menu(ClientConnection*, int menu_id, const String& name);
+    virtual ~Menu() override;
+
+    ClientConnection* client() { return m_client; }
+    const ClientConnection* client() const { return m_client; }
+    int menu_id() const { return m_menu_id; }
+
+    MenuBar* menubar() { return m_menubar; }
+    const MenuBar* menubar() const { return m_menubar; }
+    void set_menubar(MenuBar* menubar) { m_menubar = menubar; }
+
+    bool is_empty() const { return m_items.is_empty(); }
+    int item_count() const { return m_items.size(); }
+    const MenuItem& item(int index) const { return m_items.at(index); }
+    MenuItem& item(int index) { return m_items.at(index); }
+
+    void add_item(NonnullOwnPtr<MenuItem>&& item) { m_items.append(move(item)); }
+
+    String name() const { return m_name; }
+
+    template<typename Callback>
+    void for_each_item(Callback callback) const
+    {
+        for (auto& item : m_items)
+            callback(item);
+    }
+
+    Gfx::Rect text_rect_in_menubar() const { return m_text_rect_in_menubar; }
+    void set_text_rect_in_menubar(const Gfx::Rect& rect) { m_text_rect_in_menubar = rect; }
+
+    Gfx::Rect rect_in_menubar() const { return m_rect_in_menubar; }
+    void set_rect_in_menubar(const Gfx::Rect& rect) { m_rect_in_menubar = rect; }
+
+    Window* menu_window() { return m_menu_window.ptr(); }
+    Window& ensure_menu_window();
+
+    Window* window_menu_of() { return m_window_menu_of; }
+    void set_window_menu_of(Window& window) { m_window_menu_of = window.make_weak_ptr(); }
+    bool is_window_menu_open() { return m_is_window_menu_open; }
+    void set_window_menu_open(bool is_open) { m_is_window_menu_open = is_open; }
+
+    int content_width() const;
+
+    int item_height() const { return 20; }
+    int frame_thickness() const { return 3; }
+    int horizontal_padding() const { return left_padding() + right_padding(); }
+    int left_padding() const { return 14; }
+    int right_padding() const { return 14; }
+
+    void draw();
+    const Gfx::Font& font() const;
+    const Gfx::Font& title_font() const;
+    void set_title_font(const Gfx::Font& font);
+
+    MenuItem* item_with_identifier(unsigned);
+    void redraw();
+
+    MenuItem* hovered_item() const;
+    void clear_hovered_item();
+
+    Function<void(MenuItem&)> on_item_activation;
+
+    void close();
+
+    void popup(const Gfx::Point&, bool is_submenu = false);
+
+    bool is_menu_ancestor_of(const Menu&) const;
+
+    void redraw_if_theme_changed();
+
+    bool is_scrollable() const { return m_scrollable; }
+    int scroll_offset() const { return m_scroll_offset; }
+
+private:
+    virtual void event(Core::Event&) override;
+
+    RefPtr<Gfx::Font> m_title_font { &Gfx::Font::default_font() };
+
+    void handle_mouse_move_event(const MouseEvent&);
+    int visible_item_count() const;
+
+    int item_index_at(const Gfx::Point&);
+    int padding_between_text_and_shortcut() const { return 50; }
+    void did_activate(MenuItem&);
+    void open_hovered_item();
+    void update_for_new_hovered_item();
+    void descend_into_submenu_at_hovered_item();
+
+    ClientConnection* m_client { nullptr };
+    int m_menu_id { 0 };
+    String m_name;
+    Gfx::Rect m_rect_in_menubar;
+    Gfx::Rect m_text_rect_in_menubar;
+    MenuBar* m_menubar { nullptr };
+    NonnullOwnPtrVector<MenuItem> m_items;
+    RefPtr<Window> m_menu_window;
+
+    WeakPtr<Window> m_window_menu_of;
+    bool m_is_window_menu_open = { false };
+    Gfx::Point m_last_position_in_hover;
+    int m_theme_index_at_last_paint { -1 };
+    int m_hovered_item_index { -1 };
+    bool m_in_submenu { false };
+
+    bool m_scrollable { false };
+    int m_scroll_offset { 0 };
+    int m_max_scroll_offset { 0 };
+};
+
+}

Services/WindowServer/MenuBar.cpp

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "MenuBar.h"
+#include "Menu.h"
+#include "MenuItem.h"
+#include <LibGfx/Bitmap.h>
+
+namespace WindowServer {
+
+MenuBar::MenuBar(ClientConnection& client, int menubar_id)
+    : m_client(client)
+    , m_menubar_id(menubar_id)
+{
+}
+
+MenuBar::~MenuBar()
+{
+}
+
+void MenuBar::add_menu(Menu& menu)
+{
+    menu.set_menubar(this);
+
+    // NOTE: We assume that the first menu is the App menu, which has a bold font.
+    if (m_menus.is_empty())
+        menu.set_title_font(Gfx::Font::default_bold_font());
+
+    m_menus.append(&menu);
+}
+
+}

Services/WindowServer/MenuBar.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Menu.h"
+#include <AK/Vector.h>
+#include <AK/WeakPtr.h>
+#include <AK/Weakable.h>
+
+namespace WindowServer {
+
+class MenuBar : public Weakable<MenuBar> {
+public:
+    MenuBar(ClientConnection& client, int menubar_id);
+    ~MenuBar();
+
+    ClientConnection& client() { return m_client; }
+    const ClientConnection& client() const { return m_client; }
+    int menubar_id() const { return m_menubar_id; }
+    void add_menu(Menu&);
+
+    template<typename Callback>
+    void for_each_menu(Callback callback)
+    {
+        for (auto& menu : m_menus) {
+            if (callback(*menu) == IterationDecision::Break)
+                return;
+        }
+    }
+
+private:
+    ClientConnection& m_client;
+    int m_menubar_id { 0 };
+    Vector<Menu*> m_menus;
+};
+
+}

Services/WindowServer/MenuItem.cpp

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "MenuItem.h"
+#include "ClientConnection.h"
+#include "Menu.h"
+#include "WindowManager.h"
+#include <LibGfx/Bitmap.h>
+
+namespace WindowServer {
+
+MenuItem::MenuItem(Menu& menu, unsigned identifier, const String& text, const String& shortcut_text, bool enabled, bool checkable, bool checked, const Gfx::Bitmap* icon)
+    : m_menu(menu)
+    , m_type(Text)
+    , m_enabled(enabled)
+    , m_checkable(checkable)
+    , m_checked(checked)
+    , m_identifier(identifier)
+    , m_text(text)
+    , m_shortcut_text(shortcut_text)
+    , m_icon(icon)
+{
+}
+
+MenuItem::MenuItem(Menu& menu, Type type)
+    : m_menu(menu)
+    , m_type(type)
+{
+}
+
+MenuItem::~MenuItem()
+{
+}
+
+void MenuItem::set_enabled(bool enabled)
+{
+    if (m_enabled == enabled)
+        return;
+    m_enabled = enabled;
+    m_menu.redraw();
+}
+
+void MenuItem::set_checked(bool checked)
+{
+    if (m_checked == checked)
+        return;
+    m_checked = checked;
+    m_menu.redraw();
+}
+
+Menu* MenuItem::submenu()
+{
+    ASSERT(is_submenu());
+    ASSERT(m_menu.client());
+    return m_menu.client()->find_menu_by_id(m_submenu_id);
+}
+
+Gfx::Rect MenuItem::rect() const
+{
+    if (!m_menu.is_scrollable())
+        return m_rect;
+    return m_rect.translated(0, m_menu.item_height() - (m_menu.scroll_offset() * m_menu.item_height()));
+}
+
+void MenuItem::set_icon(const Gfx::Bitmap* icon)
+{
+    if (m_icon == icon)
+        return;
+    m_icon = icon;
+    m_menu.redraw();
+}
+
+}

Services/WindowServer/MenuItem.h

@@ -0,0 +1,99 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/String.h>
+#include <LibGfx/Forward.h>
+#include <LibGfx/Rect.h>
+
+namespace WindowServer {
+
+class Menu;
+
+class MenuItem {
+public:
+    enum Type {
+        None,
+        Text,
+        Separator,
+    };
+
+    MenuItem(Menu&, unsigned identifier, const String& text, const String& shortcut_text = {}, bool enabled = true, bool checkable = false, bool checked = false, const Gfx::Bitmap* icon = nullptr);
+    MenuItem(Menu&, Type);
+    ~MenuItem();
+
+    Type type() const { return m_type; }
+
+    bool is_enabled() const { return m_enabled; }
+    void set_enabled(bool);
+
+    bool is_checkable() const { return m_checkable; }
+    void set_checkable(bool checkable) { m_checkable = checkable; }
+
+    bool is_checked() const { return m_checked; }
+    void set_checked(bool);
+
+    String text() const { return m_text; }
+    void set_text(const String& text) { m_text = text; }
+
+    String shortcut_text() const { return m_shortcut_text; }
+    void set_shortcut_text(const String& text) { m_shortcut_text = text; }
+
+    void set_rect(const Gfx::Rect& rect) { m_rect = rect; }
+    Gfx::Rect rect() const;
+
+    unsigned identifier() const { return m_identifier; }
+
+    const Gfx::Bitmap* icon() const { return m_icon; }
+    void set_icon(const Gfx::Bitmap*);
+
+    bool is_submenu() const { return m_submenu_id != -1; }
+    int submenu_id() const { return m_submenu_id; }
+    void set_submenu_id(int submenu_id) { m_submenu_id = submenu_id; }
+
+    Menu* submenu();
+
+    bool is_exclusive() const { return m_exclusive; }
+    void set_exclusive(bool exclusive) { m_exclusive = exclusive; }
+
+private:
+    Menu& m_menu;
+    Type m_type { None };
+    bool m_enabled { true };
+    bool m_checkable { false };
+    bool m_checked { false };
+    unsigned m_identifier { 0 };
+    String m_text;
+    String m_shortcut_text;
+    Gfx::Rect m_rect;
+    RefPtr<Gfx::Bitmap> m_icon;
+    int m_submenu_id { -1 };
+    bool m_exclusive { false };
+};
+
+}

Services/WindowServer/MenuManager.cpp

@@ -0,0 +1,404 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020, Shannon Booth <shannon.ml.booth@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Badge.h>
+#include <AK/FileSystemPath.h>
+#include <AK/QuickSort.h>
+#include <LibCore/DirIterator.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/Painter.h>
+#include <WindowServer/AppletManager.h>
+#include <WindowServer/MenuManager.h>
+#include <WindowServer/Screen.h>
+#include <WindowServer/WindowManager.h>
+#include <unistd.h>
+
+//#define DEBUG_MENUS
+
+namespace WindowServer {
+
+static MenuManager* s_the;
+
+MenuManager& MenuManager::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
+MenuManager::MenuManager()
+{
+    s_the = this;
+    m_needs_window_resize = true;
+
+    // NOTE: This ensures that the system menu has the correct dimensions.
+    set_current_menubar(nullptr);
+
+    m_window = Window::construct(*this, WindowType::Menubar);
+    m_window->set_rect(menubar_rect());
+}
+
+MenuManager::~MenuManager()
+{
+}
+
+bool MenuManager::is_open(const Menu& menu) const
+{
+    for (size_t i = 0; i < m_open_menu_stack.size(); ++i) {
+        if (&menu == m_open_menu_stack[i].ptr())
+            return true;
+    }
+    return false;
+}
+
+void MenuManager::draw()
+{
+    auto& wm = WindowManager::the();
+    auto palette = wm.palette();
+    auto menubar_rect = this->menubar_rect();
+
+    if (m_needs_window_resize) {
+        m_window->set_rect(menubar_rect);
+        AppletManager::the().calculate_applet_rects(window());
+        m_needs_window_resize = false;
+    }
+
+    Gfx::Painter painter(*window().backing_store());
+
+    painter.fill_rect(menubar_rect, palette.window());
+    painter.draw_line({ 0, menubar_rect.bottom() }, { menubar_rect.right(), menubar_rect.bottom() }, palette.threed_shadow1());
+
+    for_each_active_menubar_menu([&](Menu& menu) {
+        Color text_color = palette.window_text();
+        if (is_open(menu)) {
+            painter.fill_rect(menu.rect_in_menubar(), palette.menu_selection());
+            painter.draw_rect(menu.rect_in_menubar(), palette.menu_selection().darkened());
+            text_color = palette.menu_selection_text();
+        }
+        painter.draw_text(
+            menu.text_rect_in_menubar(),
+            menu.name(),
+            menu.title_font(),
+            Gfx::TextAlignment::CenterLeft,
+            text_color);
+        return IterationDecision::Continue;
+    });
+
+    AppletManager::the().draw();
+}
+
+void MenuManager::refresh()
+{
+    if (!m_window)
+        return;
+    draw();
+    window().invalidate();
+}
+
+void MenuManager::event(Core::Event& event)
+{
+    if (static_cast<Event&>(event).is_mouse_event()) {
+        handle_mouse_event(static_cast<MouseEvent&>(event));
+        return;
+    }
+
+    if (static_cast<Event&>(event).is_key_event()) {
+        auto& key_event = static_cast<const KeyEvent&>(event);
+
+        if (key_event.type() == Event::KeyUp && key_event.key() == Key_Escape) {
+            close_everyone();
+            return;
+        }
+
+        if (event.type() == Event::KeyDown) {
+            for_each_active_menubar_menu([&](Menu& menu) {
+                if (is_open(menu))
+                    menu.dispatch_event(event);
+                return IterationDecision::Continue;
+            });
+        }
+    }
+
+    return Core::Object::event(event);
+}
+
+void MenuManager::handle_mouse_event(MouseEvent& mouse_event)
+{
+    auto* active_window = WindowManager::the().active_window();
+    bool handled_menubar_event = false;
+    for_each_active_menubar_menu([&](Menu& menu) {
+        if (menu.rect_in_menubar().contains(mouse_event.position())) {
+            handled_menubar_event = &menu == m_system_menu || !active_window || !active_window->is_modal();
+            if (handled_menubar_event)
+                handle_menu_mouse_event(menu, mouse_event);
+            return IterationDecision::Break;
+        }
+        return IterationDecision::Continue;
+    });
+    if (handled_menubar_event)
+        return;
+
+    if (has_open_menu()) {
+        auto* topmost_menu = m_open_menu_stack.last().ptr();
+        ASSERT(topmost_menu);
+        auto* window = topmost_menu->menu_window();
+        if (!window) {
+            dbg() << "MenuManager::handle_mouse_event: No menu window";
+            return;
+        }
+        ASSERT(window->is_visible());
+
+        bool event_is_inside_current_menu = window->rect().contains(mouse_event.position());
+        if (event_is_inside_current_menu) {
+            WindowManager::the().set_hovered_window(window);
+            auto translated_event = mouse_event.translated(-window->position());
+            WindowManager::the().deliver_mouse_event(*window, translated_event);
+            return;
+        }
+
+        if (topmost_menu->hovered_item())
+            topmost_menu->clear_hovered_item();
+        if (mouse_event.type() == Event::MouseDown || mouse_event.type() == Event::MouseUp) {
+            auto* window_menu_of = topmost_menu->window_menu_of();
+            if (window_menu_of) {
+                bool event_is_inside_taskbar_button = window_menu_of->taskbar_rect().contains(mouse_event.position());
+                if (event_is_inside_taskbar_button && !topmost_menu->is_window_menu_open()) {
+                    topmost_menu->set_window_menu_open(true);
+                    return;
+                }
+            }
+
+            if (mouse_event.type() == Event::MouseDown) {
+                close_bar();
+                topmost_menu->set_window_menu_open(false);
+            }
+        }
+
+        if (mouse_event.type() == Event::MouseMove) {
+            for (auto& menu : m_open_menu_stack) {
+                if (!menu)
+                    continue;
+                if (!menu->menu_window()->rect().contains(mouse_event.position()))
+                    continue;
+                WindowManager::the().set_hovered_window(menu->menu_window());
+                auto translated_event = mouse_event.translated(-menu->menu_window()->position());
+                WindowManager::the().deliver_mouse_event(*menu->menu_window(), translated_event);
+                break;
+            }
+        }
+        return;
+    }
+
+    AppletManager::the().dispatch_event(static_cast<Event&>(mouse_event));
+}
+
+void MenuManager::handle_menu_mouse_event(Menu& menu, const MouseEvent& event)
+{
+    bool is_hover_with_any_menu_open = event.type() == MouseEvent::MouseMove
+        && has_open_menu()
+        && (m_open_menu_stack.first()->menubar() || m_open_menu_stack.first() == m_system_menu.ptr());
+    bool is_mousedown_with_left_button = event.type() == MouseEvent::MouseDown && event.button() == MouseButton::Left;
+    bool should_open_menu = &menu != m_current_menu && (is_hover_with_any_menu_open || is_mousedown_with_left_button);
+
+    if (is_mousedown_with_left_button)
+        m_bar_open = !m_bar_open;
+
+    if (should_open_menu && m_bar_open) {
+        open_menu(menu);
+        return;
+    }
+
+    if (!m_bar_open)
+        close_everyone();
+}
+
+void MenuManager::set_needs_window_resize()
+{
+    m_needs_window_resize = true;
+}
+
+void MenuManager::close_all_menus_from_client(Badge<ClientConnection>, ClientConnection& client)
+{
+    if (!has_open_menu())
+        return;
+    if (m_open_menu_stack.first()->client() != &client)
+        return;
+    close_everyone();
+}
+
+void MenuManager::close_everyone()
+{
+    for (auto& menu : m_open_menu_stack) {
+        if (menu && menu->menu_window())
+            menu->menu_window()->set_visible(false);
+        menu->clear_hovered_item();
+    }
+    m_open_menu_stack.clear();
+    m_current_menu = nullptr;
+    refresh();
+}
+
+void MenuManager::close_everyone_not_in_lineage(Menu& menu)
+{
+    Vector<Menu*> menus_to_close;
+    for (auto& open_menu : m_open_menu_stack) {
+        if (!open_menu)
+            continue;
+        if (&menu == open_menu.ptr() || open_menu->is_menu_ancestor_of(menu))
+            continue;
+        menus_to_close.append(open_menu);
+    }
+    close_menus(menus_to_close);
+}
+
+void MenuManager::close_menus(const Vector<Menu*>& menus)
+{
+    for (auto& menu : menus) {
+        if (menu == m_current_menu)
+            m_current_menu = nullptr;
+        if (menu->menu_window())
+            menu->menu_window()->set_visible(false);
+        menu->clear_hovered_item();
+        m_open_menu_stack.remove_first_matching([&](auto& entry) {
+            return entry == menu;
+        });
+    }
+    refresh();
+}
+
+static void collect_menu_subtree(Menu& menu, Vector<Menu*>& menus)
+{
+    menus.append(&menu);
+    for (int i = 0; i < menu.item_count(); ++i) {
+        auto& item = menu.item(i);
+        if (!item.is_submenu())
+            continue;
+        collect_menu_subtree(*const_cast<MenuItem&>(item).submenu(), menus);
+    }
+}
+
+void MenuManager::close_menu_and_descendants(Menu& menu)
+{
+    Vector<Menu*> menus_to_close;
+    collect_menu_subtree(menu, menus_to_close);
+    close_menus(menus_to_close);
+}
+
+void MenuManager::toggle_menu(Menu& menu)
+{
+    if (is_open(menu)) {
+        close_menu_and_descendants(menu);
+        return;
+    }
+    open_menu(menu);
+}
+
+void MenuManager::open_menu(Menu& menu)
+{
+    if (is_open(menu))
+        return;
+    if (!menu.is_empty()) {
+        menu.redraw_if_theme_changed();
+        auto& menu_window = menu.ensure_menu_window();
+        menu_window.move_to({ menu.rect_in_menubar().x(), menu.rect_in_menubar().bottom() + 2 });
+        menu_window.set_visible(true);
+    }
+    set_current_menu(&menu);
+    refresh();
+}
+
+void MenuManager::set_current_menu(Menu* menu, bool is_submenu)
+{
+    if (menu == m_current_menu)
+        return;
+
+    if (!is_submenu) {
+        if (menu)
+            close_everyone_not_in_lineage(*menu);
+        else
+            close_everyone();
+    }
+
+    if (!menu) {
+        m_current_menu = nullptr;
+        return;
+    }
+
+    m_current_menu = menu->make_weak_ptr();
+    if (m_open_menu_stack.find([menu](auto& other) { return menu == other.ptr(); }).is_end())
+        m_open_menu_stack.append(menu->make_weak_ptr());
+}
+
+void MenuManager::close_bar()
+{
+    close_everyone();
+    m_bar_open = false;
+}
+
+Gfx::Rect MenuManager::menubar_rect() const
+{
+    return { 0, 0, Screen::the().rect().width(), 18 };
+}
+
+void MenuManager::set_current_menubar(MenuBar* menubar)
+{
+    if (menubar)
+        m_current_menubar = menubar->make_weak_ptr();
+    else
+        m_current_menubar = nullptr;
+#ifdef DEBUG_MENUS
+    dbg() << "[WM] Current menubar is now " << menubar;
+#endif
+    Gfx::Point next_menu_location { MenuManager::menubar_menu_margin() / 2, 0 };
+    for_each_active_menubar_menu([&](Menu& menu) {
+        int text_width = menu.title_font().width(menu.name());
+        menu.set_rect_in_menubar({ next_menu_location.x() - MenuManager::menubar_menu_margin() / 2, 0, text_width + MenuManager::menubar_menu_margin(), menubar_rect().height() - 1 });
+        menu.set_text_rect_in_menubar({ next_menu_location, { text_width, menubar_rect().height() } });
+        next_menu_location.move_by(menu.rect_in_menubar().width(), 0);
+        return IterationDecision::Continue;
+    });
+    refresh();
+}
+
+void MenuManager::close_menubar(MenuBar& menubar)
+{
+    if (current_menubar() == &menubar)
+        set_current_menubar(nullptr);
+}
+
+void MenuManager::set_system_menu(Menu& menu)
+{
+    m_system_menu = menu.make_weak_ptr();
+    set_current_menubar(m_current_menubar);
+}
+
+void MenuManager::did_change_theme()
+{
+    ++m_theme_index;
+    refresh();
+}
+
+}

Services/WindowServer/MenuManager.h

@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Menu.h"
+#include "MenuBar.h"
+#include "Window.h"
+#include <AK/HashMap.h>
+#include <LibCore/Object.h>
+
+namespace WindowServer {
+
+class MenuManager final : public Core::Object {
+    C_OBJECT(MenuManager)
+public:
+    static MenuManager& the();
+
+    MenuManager();
+    virtual ~MenuManager() override;
+
+    void refresh();
+
+    bool is_open(const Menu&) const;
+    bool has_open_menu() const { return !m_open_menu_stack.is_empty(); }
+
+    Gfx::Rect menubar_rect() const;
+    static int menubar_menu_margin() { return 16; }
+
+    void set_needs_window_resize();
+
+    Menu* current_menu() { return m_current_menu.ptr(); }
+    void set_current_menu(Menu*, bool is_submenu = false);
+    void open_menu(Menu&);
+    void toggle_menu(Menu&);
+
+    MenuBar* current_menubar() { return m_current_menubar.ptr(); }
+    void set_current_menubar(MenuBar*);
+    void close_menubar(MenuBar&);
+
+    void close_bar();
+    void close_everyone();
+    void close_everyone_not_in_lineage(Menu&);
+    void close_menu_and_descendants(Menu&);
+
+    void close_all_menus_from_client(Badge<ClientConnection>, ClientConnection&);
+
+    void toggle_system_menu()
+    {
+        if (m_system_menu)
+            toggle_menu(*m_system_menu);
+    }
+
+    Menu* system_menu() { return m_system_menu; }
+    void set_system_menu(Menu&);
+
+    int theme_index() const { return m_theme_index; }
+
+    Window& window() { return *m_window; }
+
+    template<typename Callback>
+    void for_each_active_menubar_menu(Callback callback)
+    {
+        if (system_menu()) {
+            if (callback(*system_menu()) == IterationDecision::Break)
+                return;
+        }
+        if (m_current_menubar)
+            m_current_menubar->for_each_menu(callback);
+    }
+
+    void did_change_theme();
+
+private:
+    void close_menus(const Vector<Menu*>&);
+
+    const Window& window() const { return *m_window; }
+
+    virtual void event(Core::Event&) override;
+    void handle_mouse_event(MouseEvent&);
+    void handle_menu_mouse_event(Menu&, const MouseEvent&);
+
+    void draw();
+
+    RefPtr<Window> m_window;
+
+    WeakPtr<Menu> m_current_menu;
+    Vector<WeakPtr<Menu>> m_open_menu_stack;
+
+    WeakPtr<Menu> m_system_menu;
+
+    bool m_needs_window_resize { false };
+    bool m_bar_open { false };
+
+    int m_theme_index { 0 };
+
+    WeakPtr<MenuBar> m_current_menubar;
+};
+
+}

Services/WindowServer/Screen.cpp

@@ -0,0 +1,171 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Screen.h"
+#include "Compositor.h"
+#include "Event.h"
+#include "EventLoop.h"
+#include "WindowManager.h"
+#include <Kernel/FB.h>
+#include <Kernel/MousePacket.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+namespace WindowServer {
+
+static Screen* s_the;
+
+Screen& Screen::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
+Screen::Screen(unsigned desired_width, unsigned desired_height)
+{
+    ASSERT(!s_the);
+    s_the = this;
+    m_framebuffer_fd = open("/dev/fb0", O_RDWR | O_CLOEXEC);
+    if (m_framebuffer_fd < 0) {
+        perror("failed to open /dev/fb0");
+        ASSERT_NOT_REACHED();
+    }
+
+    if (fb_set_buffer(m_framebuffer_fd, 0) == 0) {
+        m_can_set_buffer = true;
+    }
+
+    set_resolution(desired_width, desired_height);
+    m_cursor_location = rect().center();
+}
+
+Screen::~Screen()
+{
+}
+
+bool Screen::set_resolution(int width, int height)
+{
+    FBResolution resolution { 0, (unsigned)width, (unsigned)height };
+    int rc = fb_set_resolution(m_framebuffer_fd, &resolution);
+#ifdef WSSCREEN_DEBUG
+    dbg() << "fb_set_resolution() - return code " << rc;
+#endif
+    if (rc == 0) {
+        on_change_resolution(resolution.pitch, resolution.width, resolution.height);
+        return true;
+    }
+    if (rc == -1) {
+        dbg() << "Invalid resolution " << width << "x" << height;
+        on_change_resolution(resolution.pitch, resolution.width, resolution.height);
+        return false;
+    }
+    ASSERT_NOT_REACHED();
+}
+
+void Screen::on_change_resolution(int pitch, int width, int height)
+{
+    if (m_framebuffer) {
+        size_t previous_size_in_bytes = m_size_in_bytes;
+        int rc = munmap(m_framebuffer, previous_size_in_bytes);
+        ASSERT(rc == 0);
+    }
+
+    int rc = fb_get_size_in_bytes(m_framebuffer_fd, &m_size_in_bytes);
+    ASSERT(rc == 0);
+
+    m_framebuffer = (Gfx::RGBA32*)mmap(nullptr, m_size_in_bytes, PROT_READ | PROT_WRITE, MAP_SHARED, m_framebuffer_fd, 0);
+    ASSERT(m_framebuffer && m_framebuffer != (void*)-1);
+
+    m_pitch = pitch;
+    m_width = width;
+    m_height = height;
+
+    m_cursor_location.constrain(rect());
+}
+
+void Screen::set_buffer(int index)
+{
+    ASSERT(m_can_set_buffer);
+    int rc = fb_set_buffer(m_framebuffer_fd, index);
+    ASSERT(rc == 0);
+}
+
+void Screen::on_receive_mouse_data(const MousePacket& packet)
+{
+    auto prev_location = m_cursor_location;
+    if (packet.is_relative) {
+        m_cursor_location.move_by(packet.x, packet.y);
+#ifdef WSSCREEN_DEBUG
+        dbgprintf("Screen: New Relative mouse point @ X %d, Y %d\n", m_cursor_location.x(), m_cursor_location.y());
+#endif
+    } else {
+        m_cursor_location = { packet.x * m_width / 0xffff, packet.y * m_height / 0xffff };
+#ifdef WSSCREEN_DEBUG
+        dbgprintf("Screen: New Absolute mouse point @ X %d, Y %d\n", m_cursor_location.x(), m_cursor_location.y());
+#endif
+    }
+
+    m_cursor_location.constrain(rect());
+
+    unsigned buttons = packet.buttons;
+    unsigned prev_buttons = m_mouse_button_state;
+    m_mouse_button_state = buttons;
+    unsigned changed_buttons = prev_buttons ^ buttons;
+    auto post_mousedown_or_mouseup_if_needed = [&](MouseButton button) {
+        if (!(changed_buttons & (unsigned)button))
+            return;
+        auto message = make<MouseEvent>(buttons & (unsigned)button ? Event::MouseDown : Event::MouseUp, m_cursor_location, buttons, button, m_modifiers);
+        Core::EventLoop::current().post_event(WindowManager::the(), move(message));
+    };
+    post_mousedown_or_mouseup_if_needed(MouseButton::Left);
+    post_mousedown_or_mouseup_if_needed(MouseButton::Right);
+    post_mousedown_or_mouseup_if_needed(MouseButton::Middle);
+    post_mousedown_or_mouseup_if_needed(MouseButton::Back);
+    post_mousedown_or_mouseup_if_needed(MouseButton::Forward);
+    if (m_cursor_location != prev_location) {
+        auto message = make<MouseEvent>(Event::MouseMove, m_cursor_location, buttons, MouseButton::None, m_modifiers);
+        Core::EventLoop::current().post_event(WindowManager::the(), move(message));
+    }
+
+    if (packet.z) {
+        auto message = make<MouseEvent>(Event::MouseWheel, m_cursor_location, buttons, MouseButton::None, m_modifiers, packet.z);
+        Core::EventLoop::current().post_event(WindowManager::the(), move(message));
+    }
+
+    if (m_cursor_location != prev_location)
+        Compositor::the().invalidate_cursor();
+}
+
+void Screen::on_receive_keyboard_data(::KeyEvent kernel_event)
+{
+    m_modifiers = kernel_event.modifiers();
+    auto message = make<KeyEvent>(kernel_event.is_press() ? Event::KeyDown : Event::KeyUp, kernel_event.key, kernel_event.character, kernel_event.modifiers());
+    Core::EventLoop::current().post_event(WindowManager::the(), move(message));
+}
+
+}

Services/WindowServer/Screen.h

@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <Kernel/KeyCode.h>
+#include <LibGfx/Color.h>
+#include <LibGfx/Rect.h>
+#include <LibGfx/Size.h>
+
+struct MousePacket;
+
+namespace WindowServer {
+
+class Screen {
+public:
+    Screen(unsigned width, unsigned height);
+    ~Screen();
+
+    bool set_resolution(int width, int height);
+    bool can_set_buffer() { return m_can_set_buffer; }
+    void set_buffer(int index);
+
+    int width() const { return m_width; }
+    int height() const { return m_height; }
+    size_t pitch() const { return m_pitch; }
+    Gfx::RGBA32* scanline(int y);
+
+    static Screen& the();
+
+    Gfx::Size size() const { return { width(), height() }; }
+    Gfx::Rect rect() const { return { 0, 0, width(), height() }; }
+
+    Gfx::Point cursor_location() const { return m_cursor_location; }
+    unsigned mouse_button_state() const { return m_mouse_button_state; }
+
+    void on_receive_mouse_data(const MousePacket&);
+    void on_receive_keyboard_data(::KeyEvent);
+
+private:
+    void on_change_resolution(int pitch, int width, int height);
+
+    size_t m_size_in_bytes;
+
+    Gfx::RGBA32* m_framebuffer { nullptr };
+    bool m_can_set_buffer { false };
+
+    int m_pitch { 0 };
+    int m_width { 0 };
+    int m_height { 0 };
+    int m_framebuffer_fd { -1 };
+
+    Gfx::Point m_cursor_location;
+    unsigned m_mouse_button_state { 0 };
+    unsigned m_modifiers { 0 };
+};
+
+inline Gfx::RGBA32* Screen::scanline(int y)
+{
+    return reinterpret_cast<Gfx::RGBA32*>(((u8*)m_framebuffer) + (y * m_pitch));
+}
+
+}

Services/WindowServer/Window.cpp

@@ -0,0 +1,524 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Window.h"
+#include "ClientConnection.h"
+#include "Event.h"
+#include "EventLoop.h"
+#include "Screen.h"
+#include "WindowClientEndpoint.h"
+#include "WindowManager.h"
+#include <AK/Badge.h>
+
+namespace WindowServer {
+
+static String default_window_icon_path()
+{
+    return "/res/icons/16x16/window.png";
+}
+
+static Gfx::Bitmap& default_window_icon()
+{
+    static Gfx::Bitmap* s_icon;
+    if (!s_icon)
+        s_icon = Gfx::Bitmap::load_from_file(default_window_icon_path()).leak_ref();
+    return *s_icon;
+}
+
+static Gfx::Bitmap& minimize_icon()
+{
+    static Gfx::Bitmap* s_icon;
+    if (!s_icon)
+        s_icon = Gfx::Bitmap::load_from_file("/res/icons/16x16/window-minimize.png").leak_ref();
+    return *s_icon;
+}
+
+static Gfx::Bitmap& maximize_icon()
+{
+    static Gfx::Bitmap* s_icon;
+    if (!s_icon)
+        s_icon = Gfx::Bitmap::load_from_file("/res/icons/16x16/window-maximize.png").leak_ref();
+    return *s_icon;
+}
+
+static Gfx::Bitmap& restore_icon()
+{
+    static Gfx::Bitmap* s_icon;
+    if (!s_icon)
+        s_icon = Gfx::Bitmap::load_from_file("/res/icons/16x16/window-restore.png").leak_ref();
+    return *s_icon;
+}
+
+static Gfx::Bitmap& close_icon()
+{
+    static Gfx::Bitmap* s_icon;
+    if (!s_icon)
+        s_icon = Gfx::Bitmap::load_from_file("/res/icons/16x16/window-close.png").leak_ref();
+    return *s_icon;
+}
+
+Window::Window(Core::Object& parent, WindowType type)
+    : Core::Object(&parent)
+    , m_type(type)
+    , m_icon(default_window_icon())
+    , m_frame(*this)
+{
+    WindowManager::the().add_window(*this);
+}
+
+Window::Window(ClientConnection& client, WindowType window_type, int window_id, bool modal, bool minimizable, bool frameless, bool resizable, bool fullscreen)
+    : Core::Object(&client)
+    , m_client(&client)
+    , m_type(window_type)
+    , m_modal(modal)
+    , m_minimizable(minimizable)
+    , m_frameless(frameless)
+    , m_resizable(resizable)
+    , m_fullscreen(fullscreen)
+    , m_window_id(window_id)
+    , m_client_id(client.client_id())
+    , m_icon(default_window_icon())
+    , m_frame(*this)
+{
+    // FIXME: This should not be hard-coded here.
+    if (m_type == WindowType::Taskbar) {
+        m_wm_event_mask = WMEventMask::WindowStateChanges | WMEventMask::WindowRemovals | WMEventMask::WindowIconChanges;
+        m_listens_to_wm_events = true;
+    }
+
+    WindowManager::the().add_window(*this);
+}
+
+Window::~Window()
+{
+    // Detach from client at the start of teardown since we don't want
+    // to confuse things by trying to send messages to it.
+    m_client = nullptr;
+
+    WindowManager::the().remove_window(*this);
+}
+
+void Window::set_title(const String& title)
+{
+    if (m_title == title)
+        return;
+    m_title = title;
+    WindowManager::the().notify_title_changed(*this);
+}
+
+void Window::set_rect(const Gfx::Rect& rect)
+{
+    ASSERT(!rect.is_empty());
+    Gfx::Rect old_rect;
+    if (m_rect == rect)
+        return;
+    old_rect = m_rect;
+    m_rect = rect;
+    if (!m_client && (!m_backing_store || old_rect.size() != rect.size())) {
+        m_backing_store = Gfx::Bitmap::create(Gfx::BitmapFormat::RGB32, m_rect.size());
+    }
+    m_frame.notify_window_rect_changed(old_rect, rect);
+}
+
+void Window::set_rect_without_repaint(const Gfx::Rect& rect)
+{
+    ASSERT(!rect.is_empty());
+    if (m_rect == rect)
+        return;
+    auto old_rect = m_rect;
+    m_rect = rect;
+
+    if (old_rect.size() == m_rect.size()) {
+        auto delta = m_rect.location() - old_rect.location();
+        for (auto& child_window : m_child_windows) {
+            if (child_window)
+                child_window->move_by(delta);
+        }
+    }
+
+    m_frame.notify_window_rect_changed(old_rect, rect);
+}
+
+void Window::handle_mouse_event(const MouseEvent& event)
+{
+    set_automatic_cursor_tracking_enabled(event.buttons() != 0);
+
+    switch (event.type()) {
+    case Event::MouseMove:
+        m_client->post_message(Messages::WindowClient::MouseMove(m_window_id, event.position(), (u32)event.button(), event.buttons(), event.modifiers(), event.wheel_delta(), event.is_drag(), event.drag_data_type()));
+        break;
+    case Event::MouseDown:
+        m_client->post_message(Messages::WindowClient::MouseDown(m_window_id, event.position(), (u32)event.button(), event.buttons(), event.modifiers(), event.wheel_delta()));
+        break;
+    case Event::MouseDoubleClick:
+        m_client->post_message(Messages::WindowClient::MouseDoubleClick(m_window_id, event.position(), (u32)event.button(), event.buttons(), event.modifiers(), event.wheel_delta()));
+        break;
+    case Event::MouseUp:
+        m_client->post_message(Messages::WindowClient::MouseUp(m_window_id, event.position(), (u32)event.button(), event.buttons(), event.modifiers(), event.wheel_delta()));
+        break;
+    case Event::MouseWheel:
+        m_client->post_message(Messages::WindowClient::MouseWheel(m_window_id, event.position(), (u32)event.button(), event.buttons(), event.modifiers(), event.wheel_delta()));
+        break;
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
+void Window::update_menu_item_text(PopupMenuItem item)
+{
+    if (m_window_menu) {
+        m_window_menu->item((int)item).set_text(item == PopupMenuItem::Minimize ? (m_minimized ? "Unminimize" : "Minimize") : (m_maximized ? "Restore" : "Maximize"));
+        m_window_menu->redraw();
+    }
+}
+
+void Window::update_menu_item_enabled(PopupMenuItem item)
+{
+    if (m_window_menu) {
+        m_window_menu->item((int)item).set_enabled(item == PopupMenuItem::Minimize ? m_minimizable : m_resizable);
+        m_window_menu->redraw();
+    }
+}
+
+void Window::set_minimized(bool minimized)
+{
+    if (m_minimized == minimized)
+        return;
+    if (minimized && !m_minimizable)
+        return;
+    if (is_blocked_by_modal_window())
+        return;
+    m_minimized = minimized;
+    update_menu_item_text(PopupMenuItem::Minimize);
+    start_minimize_animation();
+    if (!minimized)
+        request_update({ {}, size() });
+    invalidate();
+    WindowManager::the().notify_minimization_state_changed(*this);
+}
+
+void Window::set_minimizable(bool minimizable)
+{
+    if (m_minimizable == minimizable)
+        return;
+    m_minimizable = minimizable;
+    update_menu_item_enabled(PopupMenuItem::Minimize);
+    // TODO: Hide/show (or alternatively change enabled state of) window minimize button dynamically depending on value of m_minimizable
+}
+
+void Window::set_opacity(float opacity)
+{
+    if (m_opacity == opacity)
+        return;
+    m_opacity = opacity;
+    WindowManager::the().notify_opacity_changed(*this);
+}
+
+void Window::set_occluded(bool occluded)
+{
+    if (m_occluded == occluded)
+        return;
+    m_occluded = occluded;
+    WindowManager::the().notify_occlusion_state_changed(*this);
+}
+
+void Window::set_maximized(bool maximized)
+{
+    if (m_maximized == maximized)
+        return;
+    if (maximized && !is_resizable())
+        return;
+    if (is_blocked_by_modal_window())
+        return;
+    set_tiled(WindowTileType::None);
+    m_maximized = maximized;
+    update_menu_item_text(PopupMenuItem::Maximize);
+    auto old_rect = m_rect;
+    if (maximized) {
+        m_unmaximized_rect = m_rect;
+        set_rect(WindowManager::the().maximized_window_rect(*this));
+    } else {
+        set_rect(m_unmaximized_rect);
+    }
+    m_frame.did_set_maximized({}, maximized);
+    Core::EventLoop::current().post_event(*this, make<ResizeEvent>(old_rect, m_rect));
+}
+
+void Window::set_resizable(bool resizable)
+{
+    if (m_resizable == resizable)
+        return;
+    m_resizable = resizable;
+    update_menu_item_enabled(PopupMenuItem::Maximize);
+    // TODO: Hide/show (or alternatively change enabled state of) window maximize button dynamically depending on value of is_resizable()
+}
+
+void Window::event(Core::Event& event)
+{
+    if (!m_client) {
+        ASSERT(parent());
+        event.ignore();
+        return;
+    }
+
+    if (is_blocked_by_modal_window())
+        return;
+
+    if (static_cast<Event&>(event).is_mouse_event())
+        return handle_mouse_event(static_cast<const MouseEvent&>(event));
+
+    switch (event.type()) {
+    case Event::WindowEntered:
+        m_client->post_message(Messages::WindowClient::WindowEntered(m_window_id));
+        break;
+    case Event::WindowLeft:
+        m_client->post_message(Messages::WindowClient::WindowLeft(m_window_id));
+        break;
+    case Event::KeyDown:
+        m_client->post_message(
+            Messages::WindowClient::KeyDown(m_window_id,
+                (u8) static_cast<const KeyEvent&>(event).character(),
+                (u32) static_cast<const KeyEvent&>(event).key(),
+                static_cast<const KeyEvent&>(event).modifiers()));
+        break;
+    case Event::KeyUp:
+        m_client->post_message(
+            Messages::WindowClient::KeyUp(m_window_id,
+                (u8) static_cast<const KeyEvent&>(event).character(),
+                (u32) static_cast<const KeyEvent&>(event).key(),
+                static_cast<const KeyEvent&>(event).modifiers()));
+        break;
+    case Event::WindowActivated:
+        m_client->post_message(Messages::WindowClient::WindowActivated(m_window_id));
+        break;
+    case Event::WindowDeactivated:
+        m_client->post_message(Messages::WindowClient::WindowDeactivated(m_window_id));
+        break;
+    case Event::WindowCloseRequest:
+        m_client->post_message(Messages::WindowClient::WindowCloseRequest(m_window_id));
+        break;
+    case Event::WindowResized:
+        m_client->post_message(
+            Messages::WindowClient::WindowResized(
+                m_window_id,
+                static_cast<const ResizeEvent&>(event).old_rect(),
+                static_cast<const ResizeEvent&>(event).rect()));
+        break;
+    default:
+        break;
+    }
+}
+
+void Window::set_global_cursor_tracking_enabled(bool enabled)
+{
+    m_global_cursor_tracking_enabled = enabled;
+}
+
+void Window::set_visible(bool b)
+{
+    if (m_visible == b)
+        return;
+    m_visible = b;
+    invalidate();
+}
+
+void Window::invalidate()
+{
+    WindowManager::the().invalidate(*this);
+}
+
+void Window::invalidate(const Gfx::Rect& rect)
+{
+    WindowManager::the().invalidate(*this, rect);
+}
+
+bool Window::is_active() const
+{
+    return WindowManager::the().active_window() == this;
+}
+
+bool Window::is_blocked_by_modal_window() const
+{
+    bool is_any_modal = false;
+    const Window* next = this;
+    while (!is_any_modal && next) {
+        is_any_modal = next->is_modal();
+        next = next->parent_window();
+    }
+
+    return !is_any_modal && client() && client()->is_showing_modal_window();
+}
+
+void Window::set_default_icon()
+{
+    m_icon = default_window_icon();
+}
+
+void Window::request_update(const Gfx::Rect& rect, bool ignore_occlusion)
+{
+    if (m_pending_paint_rects.is_empty()) {
+        deferred_invoke([this, ignore_occlusion](auto&) {
+            client()->post_paint_message(*this, ignore_occlusion);
+        });
+    }
+    m_pending_paint_rects.add(rect);
+}
+
+void Window::popup_window_menu(const Gfx::Point& position)
+{
+    if (!m_window_menu) {
+        m_window_menu = Menu::construct(nullptr, -1, "(Window Menu)");
+        m_window_menu->set_window_menu_of(*this);
+
+        auto minimize_item = make<MenuItem>(*m_window_menu, 1, m_minimized ? "Unminimize" : "Minimize");
+        m_window_menu_minimize_item = minimize_item.ptr();
+        m_window_menu->add_item(move(minimize_item));
+
+        auto maximize_item = make<MenuItem>(*m_window_menu, 2, m_maximized ? "Restore" : "Maximize");
+        m_window_menu_maximize_item = maximize_item.ptr();
+        m_window_menu->add_item(move(maximize_item));
+
+        m_window_menu->add_item(make<MenuItem>(*m_window_menu, MenuItem::Type::Separator));
+
+        auto close_item = make<MenuItem>(*m_window_menu, 3, "Close");
+        close_item->set_icon(&close_icon());
+        m_window_menu->add_item(move(close_item));
+
+        m_window_menu->item((int)PopupMenuItem::Minimize).set_enabled(m_minimizable);
+        m_window_menu->item((int)PopupMenuItem::Maximize).set_enabled(m_resizable);
+
+        m_window_menu->on_item_activation = [&](auto& item) {
+            switch (item.identifier()) {
+            case 1:
+                set_minimized(!m_minimized);
+                if (!m_minimized)
+                    WindowManager::the().move_to_front_and_make_active(*this);
+                break;
+            case 2:
+                set_maximized(!m_maximized);
+                if (m_minimized)
+                    set_minimized(false);
+                WindowManager::the().move_to_front_and_make_active(*this);
+                break;
+            case 3:
+                request_close();
+                break;
+            }
+        };
+    }
+    m_window_menu_minimize_item->set_icon(m_minimized ? nullptr : &minimize_icon());
+    m_window_menu_maximize_item->set_icon(m_maximized ? &restore_icon() : &maximize_icon());
+
+    m_window_menu->popup(position);
+}
+
+void Window::request_close()
+{
+    Event close_request(Event::WindowCloseRequest);
+    event(close_request);
+}
+
+void Window::set_fullscreen(bool fullscreen)
+{
+    if (m_fullscreen == fullscreen)
+        return;
+    m_fullscreen = fullscreen;
+    Gfx::Rect new_window_rect = m_rect;
+    if (m_fullscreen) {
+        m_saved_nonfullscreen_rect = m_rect;
+        new_window_rect = Screen::the().rect();
+    } else if (!m_saved_nonfullscreen_rect.is_empty()) {
+        new_window_rect = m_saved_nonfullscreen_rect;
+    }
+    Core::EventLoop::current().post_event(*this, make<ResizeEvent>(m_rect, new_window_rect));
+    set_rect(new_window_rect);
+}
+
+Gfx::Rect Window::tiled_rect(WindowTileType tiled) const
+{
+    int frame_width = (m_frame.rect().width() - m_rect.width()) / 2;
+    switch (tiled) {
+    case WindowTileType::None:
+        return m_untiled_rect;
+    case WindowTileType::Left:
+        return Gfx::Rect(0,
+            WindowManager::the().maximized_window_rect(*this).y(),
+            Screen::the().width() / 2 - frame_width,
+            WindowManager::the().maximized_window_rect(*this).height());
+    case WindowTileType::Right:
+        return Gfx::Rect(Screen::the().width() / 2 + frame_width,
+            WindowManager::the().maximized_window_rect(*this).y(),
+            Screen::the().width() / 2 - frame_width,
+            WindowManager::the().maximized_window_rect(*this).height());
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
+void Window::set_tiled(WindowTileType tiled)
+{
+    if (m_tiled == tiled)
+        return;
+
+    m_tiled = tiled;
+    auto old_rect = m_rect;
+    if (tiled != WindowTileType::None)
+        m_untiled_rect = m_rect;
+    set_rect(tiled_rect(tiled));
+    Core::EventLoop::current().post_event(*this, make<ResizeEvent>(old_rect, m_rect));
+}
+
+void Window::detach_client(Badge<ClientConnection>)
+{
+    m_client = nullptr;
+}
+
+void Window::recalculate_rect()
+{
+    if (!is_resizable())
+        return;
+
+    auto old_rect = m_rect;
+    if (m_tiled != WindowTileType::None)
+        set_rect(tiled_rect(m_tiled));
+    else if (is_maximized())
+        set_rect(WindowManager::the().maximized_window_rect(*this));
+    Core::EventLoop::current().post_event(*this, make<ResizeEvent>(old_rect, m_rect));
+}
+
+void Window::add_child_window(Window& child_window)
+{
+    m_child_windows.append(child_window.make_weak_ptr());
+}
+
+void Window::set_parent_window(Window& parent_window)
+{
+    ASSERT(!m_parent_window);
+    m_parent_window = parent_window.make_weak_ptr();
+    parent_window.add_child_window(*this);
+}
+
+}

Services/WindowServer/Window.h

@@ -0,0 +1,286 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/InlineLinkedList.h>
+#include <AK/String.h>
+#include <AK/WeakPtr.h>
+#include <LibCore/Object.h>
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/DisjointRectSet.h>
+#include <LibGfx/Rect.h>
+#include <WindowServer/WindowFrame.h>
+#include <WindowServer/WindowType.h>
+
+namespace WindowServer {
+
+class ClientConnection;
+class Cursor;
+class Menu;
+class MenuItem;
+class MouseEvent;
+
+enum WMEventMask {
+    WindowRectChanges = 1 << 0,
+    WindowStateChanges = 1 << 1,
+    WindowIconChanges = 1 << 2,
+    WindowRemovals = 1 << 3,
+};
+
+enum class WindowTileType {
+    None = 0,
+    Left,
+    Right,
+};
+
+enum class PopupMenuItem {
+    Minimize = 0,
+    Maximize,
+};
+
+class Window final : public Core::Object
+    , public InlineLinkedListNode<Window> {
+    C_OBJECT(Window)
+public:
+    Window(ClientConnection&, WindowType, int window_id, bool modal, bool minimizable, bool frameless, bool resizable, bool fullscreen);
+    Window(Core::Object&, WindowType);
+    virtual ~Window() override;
+
+    void popup_window_menu(const Gfx::Point&);
+    void request_close();
+
+    unsigned wm_event_mask() const { return m_wm_event_mask; }
+    void set_wm_event_mask(unsigned mask) { m_wm_event_mask = mask; }
+
+    bool is_minimized() const { return m_minimized; }
+    void set_minimized(bool);
+
+    bool is_minimizable() const { return m_minimizable; }
+    void set_minimizable(bool);
+
+    bool is_resizable() const { return m_resizable && !m_fullscreen; }
+    void set_resizable(bool);
+
+    bool is_maximized() const { return m_maximized; }
+    void set_maximized(bool);
+
+    bool is_fullscreen() const { return m_fullscreen; }
+    void set_fullscreen(bool);
+
+    WindowTileType tiled() const { return m_tiled; }
+    void set_tiled(WindowTileType);
+
+    bool is_occluded() const { return m_occluded; }
+    void set_occluded(bool);
+
+    bool is_movable() const
+    {
+        return m_type == WindowType::Normal;
+    }
+
+    WindowFrame& frame() { return m_frame; }
+    const WindowFrame& frame() const { return m_frame; }
+
+    bool is_blocked_by_modal_window() const;
+
+    bool listens_to_wm_events() const { return m_listens_to_wm_events; }
+
+    ClientConnection* client() { return m_client; }
+    const ClientConnection* client() const { return m_client; }
+
+    WindowType type() const { return m_type; }
+    int window_id() const { return m_window_id; }
+
+    bool is_internal() const { return m_client_id == -1; }
+    i32 client_id() const { return m_client_id; }
+
+    String title() const { return m_title; }
+    void set_title(const String&);
+
+    float opacity() const { return m_opacity; }
+    void set_opacity(float);
+
+    int x() const { return m_rect.x(); }
+    int y() const { return m_rect.y(); }
+    int width() const { return m_rect.width(); }
+    int height() const { return m_rect.height(); }
+
+    bool is_active() const;
+
+    bool is_visible() const { return m_visible; }
+    void set_visible(bool);
+
+    bool is_modal() const { return m_modal; }
+
+    Gfx::Rect rect() const { return m_rect; }
+    void set_rect(const Gfx::Rect&);
+    void set_rect(int x, int y, int width, int height) { set_rect({ x, y, width, height }); }
+    void set_rect_without_repaint(const Gfx::Rect&);
+
+    void set_taskbar_rect(const Gfx::Rect& rect) { m_taskbar_rect = rect; }
+    const Gfx::Rect& taskbar_rect() const { return m_taskbar_rect; }
+
+    void move_to(const Gfx::Point& position) { set_rect({ position, size() }); }
+    void move_to(int x, int y) { move_to({ x, y }); }
+
+    void move_by(const Gfx::Point& delta) { set_position_without_repaint(position().translated(delta)); }
+
+    Gfx::Point position() const { return m_rect.location(); }
+    void set_position(const Gfx::Point& position) { set_rect({ position.x(), position.y(), width(), height() }); }
+    void set_position_without_repaint(const Gfx::Point& position) { set_rect_without_repaint({ position.x(), position.y(), width(), height() }); }
+
+    Gfx::Size size() const { return m_rect.size(); }
+
+    void invalidate();
+    void invalidate(const Gfx::Rect&);
+
+    virtual void event(Core::Event&) override;
+
+    // Only used by WindowType::MenuApplet. Perhaps it could be a Window subclass? I don't know.
+    void set_rect_in_menubar(const Gfx::Rect& rect) { m_rect_in_menubar = rect; }
+    const Gfx::Rect& rect_in_menubar() const { return m_rect_in_menubar; }
+
+    const Gfx::Bitmap* backing_store() const { return m_backing_store.ptr(); }
+    Gfx::Bitmap* backing_store() { return m_backing_store.ptr(); }
+
+    void set_backing_store(RefPtr<Gfx::Bitmap>&& backing_store)
+    {
+        m_last_backing_store = move(m_backing_store);
+        m_backing_store = move(backing_store);
+    }
+
+    void swap_backing_stores()
+    {
+        swap(m_backing_store, m_last_backing_store);
+    }
+
+    Gfx::Bitmap* last_backing_store() { return m_last_backing_store.ptr(); }
+
+    void set_global_cursor_tracking_enabled(bool);
+    void set_automatic_cursor_tracking_enabled(bool enabled) { m_automatic_cursor_tracking_enabled = enabled; }
+    bool global_cursor_tracking() const { return m_global_cursor_tracking_enabled || m_automatic_cursor_tracking_enabled; }
+
+    bool has_alpha_channel() const { return m_has_alpha_channel; }
+    void set_has_alpha_channel(bool value) { m_has_alpha_channel = value; }
+
+    Gfx::Size size_increment() const { return m_size_increment; }
+    void set_size_increment(const Gfx::Size& increment) { m_size_increment = increment; }
+
+    Gfx::Size base_size() const { return m_base_size; }
+    void set_base_size(const Gfx::Size& size) { m_base_size = size; }
+
+    const Gfx::Bitmap& icon() const { return *m_icon; }
+    void set_icon(NonnullRefPtr<Gfx::Bitmap>&& icon) { m_icon = move(icon); }
+
+    void set_default_icon();
+
+    const Cursor* override_cursor() const { return m_override_cursor.ptr(); }
+    void set_override_cursor(RefPtr<Cursor>&& cursor) { m_override_cursor = move(cursor); }
+
+    void request_update(const Gfx::Rect&, bool ignore_occlusion = false);
+    Gfx::DisjointRectSet take_pending_paint_rects() { return move(m_pending_paint_rects); }
+
+    bool in_minimize_animation() const { return m_minimize_animation_step != -1; }
+
+    int minimize_animation_index() const { return m_minimize_animation_step; }
+    void step_minimize_animation() { m_minimize_animation_step += 1; }
+    void start_minimize_animation() { m_minimize_animation_step = 0; }
+    void end_minimize_animation() { m_minimize_animation_step = -1; }
+
+    Gfx::Rect tiled_rect(WindowTileType) const;
+    void recalculate_rect();
+
+    // For InlineLinkedList.
+    // FIXME: Maybe make a ListHashSet and then WindowManager can just use that.
+    Window* m_next { nullptr };
+    Window* m_prev { nullptr };
+
+    void detach_client(Badge<ClientConnection>);
+
+    Window* parent_window() { return m_parent_window; }
+    const Window* parent_window() const { return m_parent_window; }
+
+    void set_parent_window(Window&);
+
+    Vector<WeakPtr<Window>>& child_windows() { return m_child_windows; }
+    const Vector<WeakPtr<Window>>& child_windows() const { return m_child_windows; }
+
+    void set_frameless(bool frameless) { m_frameless = frameless; }
+    bool is_frameless() const { return m_frameless; }
+
+private:
+    void handle_mouse_event(const MouseEvent&);
+    void update_menu_item_text(PopupMenuItem item);
+    void update_menu_item_enabled(PopupMenuItem item);
+    void add_child_window(Window&);
+
+    ClientConnection* m_client { nullptr };
+
+    WeakPtr<Window> m_parent_window;
+    Vector<WeakPtr<Window>> m_child_windows;
+
+    String m_title;
+    Gfx::Rect m_rect;
+    Gfx::Rect m_saved_nonfullscreen_rect;
+    Gfx::Rect m_taskbar_rect;
+    WindowType m_type { WindowType::Normal };
+    bool m_global_cursor_tracking_enabled { false };
+    bool m_automatic_cursor_tracking_enabled { false };
+    bool m_visible { true };
+    bool m_has_alpha_channel { false };
+    bool m_modal { false };
+    bool m_minimizable { false };
+    bool m_frameless { false };
+    bool m_resizable { false };
+    bool m_listens_to_wm_events { false };
+    bool m_minimized { false };
+    bool m_maximized { false };
+    bool m_fullscreen { false };
+    WindowTileType m_tiled { WindowTileType::None };
+    Gfx::Rect m_untiled_rect;
+    bool m_occluded { false };
+    RefPtr<Gfx::Bitmap> m_backing_store;
+    RefPtr<Gfx::Bitmap> m_last_backing_store;
+    int m_window_id { -1 };
+    i32 m_client_id { -1 };
+    float m_opacity { 1 };
+    Gfx::Size m_size_increment;
+    Gfx::Size m_base_size;
+    NonnullRefPtr<Gfx::Bitmap> m_icon;
+    RefPtr<Cursor> m_override_cursor;
+    WindowFrame m_frame;
+    unsigned m_wm_event_mask { 0 };
+    Gfx::DisjointRectSet m_pending_paint_rects;
+    Gfx::Rect m_unmaximized_rect;
+    Gfx::Rect m_rect_in_menubar;
+    RefPtr<Menu> m_window_menu;
+    MenuItem* m_window_menu_minimize_item { nullptr };
+    MenuItem* m_window_menu_maximize_item { nullptr };
+    int m_minimize_animation_step { -1 };
+};
+
+}

Services/WindowServer/WindowClient.ipc

@@ -0,0 +1,40 @@
+endpoint WindowClient = 4
+{
+    Paint(i32 window_id, Gfx::Size window_size, Vector<Gfx::Rect> rects) =|
+    MouseMove(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta, bool is_drag, String drag_data_type) =|
+    MouseDown(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta) =|
+    MouseDoubleClick(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta) =|
+    MouseUp(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta) =|
+    MouseWheel(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta) =|
+    WindowEntered(i32 window_id) =|
+    WindowLeft(i32 window_id) =|
+    KeyDown(i32 window_id, u8 character, u32 key, u32 modifiers) =|
+    KeyUp(i32 window_id, u8 character, u32 key, u32 modifiers) =|
+    WindowActivated(i32 window_id) =|
+    WindowDeactivated(i32 window_id) =|
+    WindowStateChanged(i32 window_id, bool minimized, bool occluded) =|
+    WindowCloseRequest(i32 window_id) =|
+    WindowResized(i32 window_id, Gfx::Rect old_rect, Gfx::Rect new_rect) =|
+
+    MenuItemActivated(i32 menu_id, i32 identifier) =|
+
+    ScreenRectChanged(Gfx::Rect rect) =|
+
+    ClipboardContentsChanged(String content_type) =|
+
+    WM_WindowRemoved(i32 wm_id, i32 client_id, i32 window_id) =|
+    WM_WindowStateChanged(i32 wm_id, i32 client_id, i32 window_id, bool is_active, bool is_minimized, bool is_frameless, i32 window_type, String title, Gfx::Rect rect) =|
+    WM_WindowIconBitmapChanged(i32 wm_id, i32 client_id, i32 window_id, i32 icon_buffer_id, Gfx::Size icon_size) =|
+    WM_WindowRectChanged(i32 wm_id, i32 client_id, i32 window_id, Gfx::Rect rect) =|
+
+    AsyncSetWallpaperFinished(bool success) =|
+
+    DragAccepted() =|
+    DragCancelled() =|
+
+    DragDropped(i32 window_id, Gfx::Point mouse_position, String text, String data_type, String data) =|
+
+    UpdateSystemTheme(i32 system_theme_buffer_id) =|
+
+    DisplayLinkNotification() =|
+}

Services/WindowServer/WindowFrame.cpp

@@ -0,0 +1,414 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Badge.h>
+#include <LibGfx/CharacterBitmap.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/Painter.h>
+#include <LibGfx/StylePainter.h>
+#include <WindowServer/Button.h>
+#include <WindowServer/Compositor.h>
+#include <WindowServer/Event.h>
+#include <WindowServer/Window.h>
+#include <WindowServer/WindowFrame.h>
+#include <WindowServer/WindowManager.h>
+
+namespace WindowServer {
+
+static const int window_titlebar_height = 19;
+
+static const char* s_close_button_bitmap_data = {
+    "##    ##"
+    "###  ###"
+    " ###### "
+    "  ####  "
+    "  ####  "
+    " ###### "
+    "###  ###"
+    "##    ##"
+    "        "
+};
+
+static Gfx::CharacterBitmap* s_close_button_bitmap;
+static const int s_close_button_bitmap_width = 8;
+static const int s_close_button_bitmap_height = 9;
+
+static const char* s_minimize_button_bitmap_data = {
+    "        "
+    "        "
+    "        "
+    " ###### "
+    "  ####  "
+    "   ##   "
+    "        "
+    "        "
+    "        "
+};
+
+static Gfx::CharacterBitmap* s_minimize_button_bitmap;
+static const int s_minimize_button_bitmap_width = 8;
+static const int s_minimize_button_bitmap_height = 9;
+
+static const char* s_maximize_button_bitmap_data = {
+    "        "
+    "        "
+    "        "
+    "   ##   "
+    "  ####  "
+    " ###### "
+    "        "
+    "        "
+    "        "
+};
+
+static Gfx::CharacterBitmap* s_maximize_button_bitmap;
+static const int s_maximize_button_bitmap_width = 8;
+static const int s_maximize_button_bitmap_height = 9;
+
+static const char* s_unmaximize_button_bitmap_data = {
+    "        "
+    "   ##   "
+    "  ####  "
+    " ###### "
+    "        "
+    " ###### "
+    "  ####  "
+    "   ##   "
+    "        "
+};
+
+static Gfx::CharacterBitmap* s_unmaximize_button_bitmap;
+static const int s_unmaximize_button_bitmap_width = 8;
+static const int s_unmaximize_button_bitmap_height = 9;
+
+WindowFrame::WindowFrame(Window& window)
+    : m_window(window)
+{
+    if (!s_close_button_bitmap)
+        s_close_button_bitmap = &Gfx::CharacterBitmap::create_from_ascii(s_close_button_bitmap_data, s_close_button_bitmap_width, s_close_button_bitmap_height).leak_ref();
+
+    if (!s_minimize_button_bitmap)
+        s_minimize_button_bitmap = &Gfx::CharacterBitmap::create_from_ascii(s_minimize_button_bitmap_data, s_minimize_button_bitmap_width, s_minimize_button_bitmap_height).leak_ref();
+
+    if (!s_maximize_button_bitmap)
+        s_maximize_button_bitmap = &Gfx::CharacterBitmap::create_from_ascii(s_maximize_button_bitmap_data, s_maximize_button_bitmap_width, s_maximize_button_bitmap_height).leak_ref();
+
+    if (!s_unmaximize_button_bitmap)
+        s_unmaximize_button_bitmap = &Gfx::CharacterBitmap::create_from_ascii(s_unmaximize_button_bitmap_data, s_unmaximize_button_bitmap_width, s_unmaximize_button_bitmap_height).leak_ref();
+
+    m_buttons.append(make<Button>(*this, *s_close_button_bitmap, [this](auto&) {
+        m_window.request_close();
+    }));
+
+    if (window.is_resizable()) {
+        auto button = make<Button>(*this, *s_maximize_button_bitmap, [this](auto&) {
+            m_window.set_maximized(!m_window.is_maximized());
+        });
+        m_maximize_button = button.ptr();
+        m_buttons.append(move(button));
+    }
+
+    if (window.is_minimizable()) {
+        auto button = make<Button>(*this, *s_minimize_button_bitmap, [this](auto&) {
+            m_window.set_minimized(true);
+        });
+        m_minimize_button = button.ptr();
+        m_buttons.append(move(button));
+    }
+}
+
+WindowFrame::~WindowFrame()
+{
+}
+
+void WindowFrame::did_set_maximized(Badge<Window>, bool maximized)
+{
+    ASSERT(m_maximize_button);
+    m_maximize_button->set_bitmap(maximized ? *s_unmaximize_button_bitmap : *s_maximize_button_bitmap);
+}
+
+Gfx::Rect WindowFrame::title_bar_rect() const
+{
+    if (m_window.type() == WindowType::Notification)
+        return { m_window.width() + 3, 3, window_titlebar_height, m_window.height() };
+    return { 4, 4, m_window.width(), window_titlebar_height };
+}
+
+Gfx::Rect WindowFrame::title_bar_icon_rect() const
+{
+    auto titlebar_rect = title_bar_rect();
+    return {
+        titlebar_rect.x() + 1,
+        titlebar_rect.y() + 2,
+        16,
+        titlebar_rect.height(),
+    };
+}
+
+Gfx::Rect WindowFrame::title_bar_text_rect() const
+{
+    auto titlebar_rect = title_bar_rect();
+    auto titlebar_icon_rect = title_bar_icon_rect();
+    return {
+        titlebar_rect.x() + 2 + titlebar_icon_rect.width() + 2,
+        titlebar_rect.y(),
+        titlebar_rect.width() - 4 - titlebar_icon_rect.width() - 2,
+        titlebar_rect.height()
+    };
+}
+
+WindowFrame::FrameColors WindowFrame::compute_frame_colors() const
+{
+    auto& wm = WindowManager::the();
+    auto palette = wm.palette();
+    if (&m_window == wm.m_highlight_window)
+        return { palette.highlight_window_title(), palette.highlight_window_border1(), palette.highlight_window_border2() };
+    if (&m_window == wm.m_move_window)
+        return { palette.moving_window_title(), palette.moving_window_border1(), palette.moving_window_border2() };
+    if (&m_window == wm.m_active_window)
+        return { palette.active_window_title(), palette.active_window_border1(), palette.active_window_border2() };
+    return { palette.inactive_window_title(), palette.inactive_window_border1(), palette.inactive_window_border2() };
+}
+
+void WindowFrame::paint_notification_frame(Gfx::Painter& painter)
+{
+    auto palette = WindowManager::the().palette();
+    Gfx::Rect outer_rect = { {}, rect().size() };
+
+    Gfx::StylePainter::paint_window_frame(painter, outer_rect, palette);
+
+    auto titlebar_rect = title_bar_rect();
+    painter.fill_rect_with_gradient(Gfx::Orientation::Vertical, titlebar_rect, palette.active_window_border1(), palette.active_window_border2());
+
+    int stripe_top = m_buttons.last().relative_rect().bottom() + 4;
+    int stripe_bottom = m_window.height() - 3;
+    if (stripe_top && stripe_bottom && stripe_top < stripe_bottom) {
+        for (int i = 2; i <= window_titlebar_height - 2; i += 2) {
+            painter.draw_line({ titlebar_rect.x() + i, stripe_top }, { titlebar_rect.x() + i, stripe_bottom }, palette.active_window_border1());
+        }
+    }
+}
+
+void WindowFrame::paint_normal_frame(Gfx::Painter& painter)
+{
+    auto palette = WindowManager::the().palette();
+    auto& window = m_window;
+    Gfx::Rect outer_rect = { {}, rect().size() };
+
+    Gfx::StylePainter::paint_window_frame(painter, outer_rect, palette);
+
+    auto titlebar_rect = title_bar_rect();
+    auto titlebar_icon_rect = title_bar_icon_rect();
+    auto titlebar_inner_rect = title_bar_text_rect();
+    auto titlebar_title_rect = titlebar_inner_rect;
+    titlebar_title_rect.set_width(Gfx::Font::default_bold_font().width(window.title()));
+
+    auto [title_color, border_color, border_color2] = compute_frame_colors();
+
+    auto& wm = WindowManager::the();
+    painter.draw_line(titlebar_rect.bottom_left().translated(0, 1), titlebar_rect.bottom_right().translated(0, 1), palette.button());
+    painter.draw_line(titlebar_rect.bottom_left().translated(0, 2), titlebar_rect.bottom_right().translated(0, 2), palette.button());
+
+    auto leftmost_button_rect = m_buttons.is_empty() ? Gfx::Rect() : m_buttons.last().relative_rect();
+
+    painter.fill_rect_with_gradient(titlebar_rect, border_color, border_color2);
+
+    int stripe_left = titlebar_title_rect.right() + 4;
+    int stripe_right = leftmost_button_rect.left() - 3;
+    if (stripe_left && stripe_right && stripe_left < stripe_right) {
+        for (int i = 2; i <= titlebar_inner_rect.height() - 2; i += 2) {
+            painter.draw_line({ stripe_left, titlebar_inner_rect.y() + i }, { stripe_right, titlebar_inner_rect.y() + i }, border_color);
+        }
+    }
+
+    auto clipped_title_rect = titlebar_title_rect;
+    clipped_title_rect.set_width(stripe_right - clipped_title_rect.x());
+    if (!clipped_title_rect.is_empty()) {
+        painter.draw_text(clipped_title_rect.translated(1, 2), window.title(), wm.window_title_font(), Gfx::TextAlignment::CenterLeft, border_color.darkened(0.4), Gfx::TextElision::Right);
+        // FIXME: The translated(0, 1) wouldn't be necessary if we could center text based on its baseline.
+        painter.draw_text(clipped_title_rect.translated(0, 1), window.title(), wm.window_title_font(), Gfx::TextAlignment::CenterLeft, title_color, Gfx::TextElision::Right);
+    }
+
+    painter.blit(titlebar_icon_rect.location(), window.icon(), window.icon().rect());
+}
+
+void WindowFrame::paint(Gfx::Painter& painter)
+{
+    if (m_window.is_frameless())
+        return;
+
+    Gfx::PainterStateSaver saver(painter);
+    painter.translate(rect().location());
+
+    if (m_window.type() == WindowType::Notification)
+        paint_notification_frame(painter);
+    else if (m_window.type() == WindowType::Normal)
+        paint_normal_frame(painter);
+    else
+        return;
+
+    for (auto& button : m_buttons) {
+        button.paint(painter);
+    }
+}
+
+static Gfx::Rect frame_rect_for_window(Window& window, const Gfx::Rect& rect)
+{
+    if (window.is_frameless())
+        return rect;
+
+    auto type = window.type();
+
+    switch (type) {
+    case WindowType::Normal:
+        return {
+            rect.x() - 4,
+            rect.y() - window_titlebar_height - 6,
+            rect.width() + 8,
+            rect.height() + 10 + window_titlebar_height
+        };
+    case WindowType::Notification:
+        return {
+            rect.x() - 3,
+            rect.y() - 3,
+            rect.width() + 6 + window_titlebar_height,
+            rect.height() + 6
+        };
+    default:
+        return rect;
+    }
+}
+
+static Gfx::Rect frame_rect_for_window(Window& window)
+{
+    return frame_rect_for_window(window, window.rect());
+}
+
+Gfx::Rect WindowFrame::rect() const
+{
+    return frame_rect_for_window(m_window);
+}
+
+void WindowFrame::invalidate_title_bar()
+{
+    WindowManager::the().invalidate(title_bar_rect().translated(rect().location()));
+}
+
+void WindowFrame::notify_window_rect_changed(const Gfx::Rect& old_rect, const Gfx::Rect& new_rect)
+{
+    int window_button_width = 15;
+    int window_button_height = 15;
+    int pos;
+    if (m_window.type() == WindowType::Notification)
+        pos = title_bar_rect().top() + 2;
+    else
+        pos = title_bar_text_rect().right() + 1;
+
+    for (auto& button : m_buttons) {
+        if (m_window.type() == WindowType::Notification) {
+            Gfx::Rect rect { 0, pos, window_button_width, window_button_height };
+            rect.center_horizontally_within(title_bar_rect());
+            button.set_relative_rect(rect);
+            pos += window_button_width;
+        } else {
+            pos -= window_button_width;
+            Gfx::Rect rect { pos, 0, window_button_width, window_button_height };
+            rect.center_vertically_within(title_bar_text_rect());
+            button.set_relative_rect(rect);
+        }
+    }
+
+    auto& wm = WindowManager::the();
+    wm.invalidate(frame_rect_for_window(m_window, old_rect));
+    wm.invalidate(frame_rect_for_window(m_window, new_rect));
+    wm.notify_rect_changed(m_window, old_rect, new_rect);
+}
+
+void WindowFrame::on_mouse_event(const MouseEvent& event)
+{
+    ASSERT(!m_window.is_fullscreen());
+
+    if (m_window.is_blocked_by_modal_window())
+        return;
+
+    auto& wm = WindowManager::the();
+    if (m_window.type() != WindowType::Normal && m_window.type() != WindowType::Notification)
+        return;
+
+    if (m_window.type() == WindowType::Normal && event.type() == Event::MouseDown && (event.button() == MouseButton::Left || event.button() == MouseButton::Right) && title_bar_icon_rect().contains(event.position())) {
+        wm.move_to_front_and_make_active(m_window);
+        m_window.popup_window_menu(title_bar_rect().bottom_left().translated(rect().location()));
+        return;
+    }
+
+    // This is slightly hackish, but expand the title bar rect by two pixels downwards,
+    // so that mouse events between the title bar and window contents don't act like
+    // mouse events on the border.
+    auto adjusted_title_bar_rect = title_bar_rect();
+    adjusted_title_bar_rect.set_height(adjusted_title_bar_rect.height() + 2);
+
+    if (adjusted_title_bar_rect.contains(event.position())) {
+        wm.clear_resize_candidate();
+
+        if (event.type() == Event::MouseDown)
+            wm.move_to_front_and_make_active(m_window);
+
+        for (auto& button : m_buttons) {
+            if (button.relative_rect().contains(event.position()))
+                return button.on_mouse_event(event.translated(-button.relative_rect().location()));
+        }
+        if (event.type() == Event::MouseDown) {
+            if (m_window.type() == WindowType::Normal && event.button() == MouseButton::Right) {
+                m_window.popup_window_menu(event.position().translated(rect().location()));
+                return;
+            }
+            if (m_window.is_movable() && event.button() == MouseButton::Left)
+                wm.start_window_move(m_window, event.translated(rect().location()));
+        }
+        return;
+    }
+
+    if (m_window.is_resizable() && event.type() == Event::MouseMove && event.buttons() == 0) {
+        constexpr ResizeDirection direction_for_hot_area[3][3] = {
+            { ResizeDirection::UpLeft, ResizeDirection::Up, ResizeDirection::UpRight },
+            { ResizeDirection::Left, ResizeDirection::None, ResizeDirection::Right },
+            { ResizeDirection::DownLeft, ResizeDirection::Down, ResizeDirection::DownRight },
+        };
+        Gfx::Rect outer_rect = { {}, rect().size() };
+        ASSERT(outer_rect.contains(event.position()));
+        int window_relative_x = event.x() - outer_rect.x();
+        int window_relative_y = event.y() - outer_rect.y();
+        int hot_area_row = min(2, window_relative_y / (outer_rect.height() / 3));
+        int hot_area_column = min(2, window_relative_x / (outer_rect.width() / 3));
+        wm.set_resize_candidate(m_window, direction_for_hot_area[hot_area_row][hot_area_column]);
+        Compositor::the().invalidate_cursor();
+        return;
+    }
+
+    if (m_window.is_resizable() && event.type() == Event::MouseDown && event.button() == MouseButton::Left)
+        wm.start_window_resize(m_window, event.translated(rect().location()));
+}
+}

Services/WindowServer/WindowFrame.h

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <AK/NonnullOwnPtrVector.h>
+#include <LibGfx/Forward.h>
+
+namespace WindowServer {
+
+class Button;
+class MouseEvent;
+class Window;
+
+class WindowFrame {
+public:
+    WindowFrame(Window&);
+    ~WindowFrame();
+
+    Gfx::Rect rect() const;
+    void paint(Gfx::Painter&);
+    void on_mouse_event(const MouseEvent&);
+    void notify_window_rect_changed(const Gfx::Rect& old_rect, const Gfx::Rect& new_rect);
+    void invalidate_title_bar();
+
+    Gfx::Rect title_bar_rect() const;
+    Gfx::Rect title_bar_icon_rect() const;
+    Gfx::Rect title_bar_text_rect() const;
+
+    void did_set_maximized(Badge<Window>, bool);
+
+private:
+    void paint_notification_frame(Gfx::Painter&);
+    void paint_normal_frame(Gfx::Painter&);
+
+    struct FrameColors {
+        Color title_color;
+        Color border_color;
+        Color border_color2;
+    };
+
+    FrameColors compute_frame_colors() const;
+
+    Window& m_window;
+    NonnullOwnPtrVector<Button> m_buttons;
+    Button* m_maximize_button { nullptr };
+    Button* m_minimize_button { nullptr };
+};
+
+}

Services/WindowServer/WindowManager.h

@@ -0,0 +1,416 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/HashMap.h>
+#include <AK/HashTable.h>
+#include <AK/InlineLinkedList.h>
+#include <AK/WeakPtr.h>
+#include <LibCore/ConfigFile.h>
+#include <LibCore/ElapsedTimer.h>
+#include <LibGfx/Color.h>
+#include <LibGfx/DisjointRectSet.h>
+#include <LibGfx/Painter.h>
+#include <LibGfx/Palette.h>
+#include <LibGfx/Rect.h>
+#include <WindowServer/Cursor.h>
+#include <WindowServer/Event.h>
+#include <WindowServer/MenuBar.h>
+#include <WindowServer/MenuManager.h>
+#include <WindowServer/Window.h>
+#include <WindowServer/WindowSwitcher.h>
+#include <WindowServer/WindowType.h>
+
+namespace WindowServer {
+
+class Screen;
+class MouseEvent;
+class Window;
+class ClientConnection;
+class WindowSwitcher;
+class Button;
+
+enum class ResizeDirection {
+    None,
+    Left,
+    UpLeft,
+    Up,
+    UpRight,
+    Right,
+    DownRight,
+    Down,
+    DownLeft
+};
+
+class WindowManager : public Core::Object {
+    C_OBJECT(WindowManager)
+
+    friend class Compositor;
+    friend class WindowFrame;
+    friend class WindowSwitcher;
+
+public:
+    static WindowManager& the();
+
+    explicit WindowManager(const Gfx::PaletteImpl&);
+    virtual ~WindowManager() override;
+
+    Palette palette() const { return Palette(*m_palette); }
+
+    RefPtr<Core::ConfigFile> wm_config() const
+    {
+        return m_wm_config;
+    }
+    void reload_config(bool);
+
+    void add_window(Window&);
+    void remove_window(Window&);
+
+    void notify_title_changed(Window&);
+    void notify_rect_changed(Window&, const Gfx::Rect& oldRect, const Gfx::Rect& newRect);
+    void notify_minimization_state_changed(Window&);
+    void notify_opacity_changed(Window&);
+    void notify_occlusion_state_changed(Window&);
+    void notify_client_changed_app_menubar(ClientConnection&);
+
+    Gfx::Rect maximized_window_rect(const Window&) const;
+
+    ClientConnection* dnd_client() { return m_dnd_client.ptr(); }
+    const String& dnd_text() const { return m_dnd_text; }
+    const String& dnd_data_type() const { return m_dnd_data_type; }
+    const String& dnd_data() const { return m_dnd_data; }
+    const Gfx::Bitmap* dnd_bitmap() const { return m_dnd_bitmap; }
+    Gfx::Rect dnd_rect() const;
+
+    void start_dnd_drag(ClientConnection&, const String& text, Gfx::Bitmap*, const String& data_type, const String& data);
+    void end_dnd_drag();
+
+    Window* active_window() { return m_active_window.ptr(); }
+    const ClientConnection* active_client() const;
+    bool active_window_is_modal() const { return m_active_window && m_active_window->is_modal(); }
+
+    Window* highlight_window() { return m_highlight_window.ptr(); }
+    void set_highlight_window(Window*);
+
+    void move_to_front_and_make_active(Window&);
+
+    Gfx::Rect menubar_rect() const;
+    Gfx::Rect desktop_rect() const;
+
+    const Cursor& active_cursor() const;
+    const Cursor& arrow_cursor() const { return *m_arrow_cursor; }
+    const Cursor& hand_cursor() const { return *m_hand_cursor; }
+    const Cursor& resize_horizontally_cursor() const { return *m_resize_horizontally_cursor; }
+    const Cursor& resize_vertically_cursor() const { return *m_resize_vertically_cursor; }
+    const Cursor& resize_diagonally_tlbr_cursor() const { return *m_resize_diagonally_tlbr_cursor; }
+    const Cursor& resize_diagonally_bltr_cursor() const { return *m_resize_diagonally_bltr_cursor; }
+    const Cursor& i_beam_cursor() const { return *m_i_beam_cursor; }
+    const Cursor& disallowed_cursor() const { return *m_disallowed_cursor; }
+    const Cursor& move_cursor() const { return *m_move_cursor; }
+    const Cursor& drag_cursor() const { return *m_drag_cursor; }
+
+    void invalidate(const Window&);
+    void invalidate(const Window&, const Gfx::Rect&);
+    void invalidate(const Gfx::Rect&);
+    void invalidate();
+    void flush(const Gfx::Rect&);
+
+    const Gfx::Font& font() const;
+    const Gfx::Font& window_title_font() const;
+
+    bool set_resolution(int width, int height);
+    Gfx::Size resolution() const;
+
+    void set_active_window(Window*);
+    void set_hovered_button(Button*);
+
+    Button* cursor_tracking_button() { return m_cursor_tracking_button.ptr(); }
+    void set_cursor_tracking_button(Button*);
+
+    void set_resize_candidate(Window&, ResizeDirection);
+    void clear_resize_candidate();
+    ResizeDirection resize_direction_of_window(const Window&);
+
+    bool any_opaque_window_contains_rect(const Gfx::Rect&);
+    bool any_opaque_window_above_this_one_contains_rect(const Window&, const Gfx::Rect&);
+
+    void tell_wm_listeners_window_state_changed(Window&);
+    void tell_wm_listeners_window_icon_changed(Window&);
+    void tell_wm_listeners_window_rect_changed(Window&);
+
+    void start_window_resize(Window&, const Gfx::Point&, MouseButton);
+    void start_window_resize(Window&, const MouseEvent&);
+
+    const Window* active_fullscreen_window() const { return (m_active_window && m_active_window->is_fullscreen()) ? m_active_window : nullptr; }
+    Window* active_fullscreen_window() { return (m_active_window && m_active_window->is_fullscreen()) ? m_active_window : nullptr; }
+
+    bool update_theme(String theme_path, String theme_name);
+
+    void set_hovered_window(Window*);
+    void deliver_mouse_event(Window& window, MouseEvent& event);
+
+private:
+    NonnullRefPtr<Cursor> get_cursor(const String& name);
+    NonnullRefPtr<Cursor> get_cursor(const String& name, const Gfx::Point& hotspot);
+
+    void process_mouse_event(MouseEvent&, Window*& hovered_window);
+    void process_event_for_doubleclick(Window& window, MouseEvent& event);
+    bool process_ongoing_window_resize(const MouseEvent&, Window*& hovered_window);
+    bool process_ongoing_window_move(MouseEvent&, Window*& hovered_window);
+    bool process_ongoing_drag(MouseEvent&, Window*& hovered_window);
+    void start_window_move(Window&, const MouseEvent&);
+    template<typename Callback>
+    IterationDecision for_each_visible_window_of_type_from_back_to_front(WindowType, Callback, bool ignore_highlight = false);
+    template<typename Callback>
+    IterationDecision for_each_visible_window_of_type_from_front_to_back(WindowType, Callback, bool ignore_highlight = false);
+    template<typename Callback>
+    IterationDecision for_each_visible_window_from_front_to_back(Callback);
+    template<typename Callback>
+    IterationDecision for_each_visible_window_from_back_to_front(Callback);
+    template<typename Callback>
+    void for_each_window_listening_to_wm_events(Callback);
+    template<typename Callback>
+    void for_each_window(Callback);
+    template<typename Callback>
+    IterationDecision for_each_window_of_type_from_front_to_back(WindowType, Callback, bool ignore_highlight = false);
+
+    virtual void event(Core::Event&) override;
+    void paint_window_frame(const Window&);
+    void tell_wm_listener_about_window(Window& listener, Window&);
+    void tell_wm_listener_about_window_icon(Window& listener, Window&);
+    void tell_wm_listener_about_window_rect(Window& listener, Window&);
+    void pick_new_active_window();
+
+    void recompute_occlusions();
+
+    RefPtr<Cursor> m_arrow_cursor;
+    RefPtr<Cursor> m_hand_cursor;
+    RefPtr<Cursor> m_resize_horizontally_cursor;
+    RefPtr<Cursor> m_resize_vertically_cursor;
+    RefPtr<Cursor> m_resize_diagonally_tlbr_cursor;
+    RefPtr<Cursor> m_resize_diagonally_bltr_cursor;
+    RefPtr<Cursor> m_i_beam_cursor;
+    RefPtr<Cursor> m_disallowed_cursor;
+    RefPtr<Cursor> m_move_cursor;
+    RefPtr<Cursor> m_drag_cursor;
+
+    InlineLinkedList<Window> m_windows_in_order;
+
+    struct DoubleClickInfo {
+        struct ClickMetadata {
+            Core::ElapsedTimer clock;
+            Gfx::Point last_position;
+        };
+
+        ClickMetadata& metadata_for_button(MouseButton);
+
+        void reset()
+        {
+            m_left = {};
+            m_right = {};
+            m_middle = {};
+            m_back = {};
+            m_forward = {};
+        }
+
+        WeakPtr<Window> m_clicked_window;
+
+    private:
+        ClickMetadata m_left;
+        ClickMetadata m_right;
+        ClickMetadata m_middle;
+        ClickMetadata m_back;
+        ClickMetadata m_forward;
+    };
+    DoubleClickInfo m_double_click_info;
+    int m_double_click_speed { 0 };
+    int m_max_distance_for_double_click { 4 };
+
+    WeakPtr<Window> m_active_window;
+    WeakPtr<Window> m_hovered_window;
+    WeakPtr<Window> m_highlight_window;
+    WeakPtr<Window> m_active_input_window;
+
+    WeakPtr<Window> m_move_window;
+    Gfx::Point m_move_origin;
+    Gfx::Point m_move_window_origin;
+
+    WeakPtr<Window> m_resize_window;
+    WeakPtr<Window> m_resize_candidate;
+    MouseButton m_resizing_mouse_button { MouseButton::None };
+    Gfx::Rect m_resize_window_original_rect;
+    Gfx::Point m_resize_origin;
+    ResizeDirection m_resize_direction { ResizeDirection::None };
+
+    bool m_moved_or_resized_since_logo_keydown { false };
+
+    u8 m_keyboard_modifiers { 0 };
+
+    WindowSwitcher m_switcher;
+
+    WeakPtr<Button> m_cursor_tracking_button;
+    WeakPtr<Button> m_hovered_button;
+
+    NonnullRefPtr<Gfx::PaletteImpl> m_palette;
+
+    RefPtr<Core::ConfigFile> m_wm_config;
+
+    WeakPtr<ClientConnection> m_dnd_client;
+    String m_dnd_text;
+    String m_dnd_data_type;
+    String m_dnd_data;
+    RefPtr<Gfx::Bitmap> m_dnd_bitmap;
+};
+
+template<typename Callback>
+IterationDecision WindowManager::for_each_visible_window_of_type_from_back_to_front(WindowType type, Callback callback, bool ignore_highlight)
+{
+    bool do_highlight_window_at_end = false;
+    for (auto& window : m_windows_in_order) {
+        if (!window.is_visible())
+            continue;
+        if (window.is_minimized())
+            continue;
+        if (window.type() != type)
+            continue;
+        if (!ignore_highlight && m_highlight_window == &window) {
+            do_highlight_window_at_end = true;
+            continue;
+        }
+        if (callback(window) == IterationDecision::Break)
+            return IterationDecision::Break;
+    }
+    if (do_highlight_window_at_end) {
+        if (callback(*m_highlight_window) == IterationDecision::Break)
+            return IterationDecision::Break;
+    }
+    return IterationDecision::Continue;
+}
+
+template<typename Callback>
+IterationDecision WindowManager::for_each_visible_window_from_back_to_front(Callback callback)
+{
+    if (for_each_visible_window_of_type_from_back_to_front(WindowType::Desktop, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_back_to_front(WindowType::Normal, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_back_to_front(WindowType::Taskbar, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_back_to_front(WindowType::Tooltip, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_back_to_front(WindowType::Notification, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_back_to_front(WindowType::Menubar, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_back_to_front(WindowType::Menu, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    return for_each_visible_window_of_type_from_back_to_front(WindowType::WindowSwitcher, callback);
+}
+
+template<typename Callback>
+IterationDecision WindowManager::for_each_visible_window_of_type_from_front_to_back(WindowType type, Callback callback, bool ignore_highlight)
+{
+    if (!ignore_highlight && m_highlight_window && m_highlight_window->type() == type && m_highlight_window->is_visible()) {
+        if (callback(*m_highlight_window) == IterationDecision::Break)
+            return IterationDecision::Break;
+    }
+
+    for (auto* window = m_windows_in_order.tail(); window; window = window->prev()) {
+        if (!window->is_visible())
+            continue;
+        if (window->is_minimized())
+            continue;
+        if (window->type() != type)
+            continue;
+        if (!ignore_highlight && window == m_highlight_window)
+            continue;
+        if (callback(*window) == IterationDecision::Break)
+            return IterationDecision::Break;
+    }
+    return IterationDecision::Continue;
+}
+
+template<typename Callback>
+IterationDecision WindowManager::for_each_visible_window_from_front_to_back(Callback callback)
+{
+    if (for_each_visible_window_of_type_from_front_to_back(WindowType::WindowSwitcher, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_front_to_back(WindowType::Menu, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_front_to_back(WindowType::Menubar, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_front_to_back(WindowType::Notification, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_front_to_back(WindowType::Tooltip, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_front_to_back(WindowType::Taskbar, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    if (for_each_visible_window_of_type_from_front_to_back(WindowType::Normal, callback) == IterationDecision::Break)
+        return IterationDecision::Break;
+    return for_each_visible_window_of_type_from_front_to_back(WindowType::Desktop, callback);
+}
+
+template<typename Callback>
+void WindowManager::for_each_window_listening_to_wm_events(Callback callback)
+{
+    for (auto* window = m_windows_in_order.tail(); window; window = window->prev()) {
+        if (!window->listens_to_wm_events())
+            continue;
+        if (callback(*window) == IterationDecision::Break)
+            return;
+    }
+}
+
+template<typename Callback>
+void WindowManager::for_each_window(Callback callback)
+{
+    for (auto* window = m_windows_in_order.tail(); window; window = window->prev()) {
+        if (callback(*window) == IterationDecision::Break)
+            return;
+    }
+}
+
+template<typename Callback>
+IterationDecision WindowManager::for_each_window_of_type_from_front_to_back(WindowType type, Callback callback, bool ignore_highlight)
+{
+    if (!ignore_highlight && m_highlight_window && m_highlight_window->type() == type && m_highlight_window->is_visible()) {
+        if (callback(*m_highlight_window) == IterationDecision::Break)
+            return IterationDecision::Break;
+    }
+
+    for (auto* window = m_windows_in_order.tail(); window; window = window->prev()) {
+        if (window->type() != type)
+            continue;
+        if (!ignore_highlight && window == m_highlight_window)
+            continue;
+        if (callback(*window) == IterationDecision::Break)
+            return IterationDecision::Break;
+    }
+    return IterationDecision::Continue;
+}
+
+}

Services/WindowServer/WindowServer.ipc

@@ -0,0 +1,97 @@
+endpoint WindowServer = 2
+{
+    Greet() => (i32 client_id, Gfx::Rect screen_rect, i32 system_theme_buffer_id)
+
+    CreateMenubar() => (i32 menubar_id)
+    DestroyMenubar(i32 menubar_id) => ()
+
+    CreateMenu(String menu_title) => (i32 menu_id)
+    DestroyMenu(i32 menu_id) => ()
+
+    AddMenuToMenubar(i32 menubar_id, i32 menu_id) => ()
+    SetApplicationMenubar(i32 menubar_id) => ()
+
+    SetSystemMenu(i32 menu_id) => ()
+
+    AddMenuItem(
+        i32 menu_id,
+        i32 identifier,
+        i32 submenu_id,
+        String text,
+        bool enabled,
+        bool checkable,
+        bool checked,
+        String shortcut,
+        i32 icon_buffer_id,
+        bool exclusive) => ()
+
+    AddMenuSeparator(i32 menu_id) => ()
+
+    UpdateMenuItem(i32 menu_id, i32 identifier, i32 submenu_id, String text, bool enabled, bool checkable, bool checked, String shortcut) => ()
+
+    CreateWindow(
+        Gfx::Rect rect,
+        bool has_alpha_channel,
+        bool modal,
+        bool minimizable,
+        bool resizable,
+        bool fullscreen,
+        bool frameless,
+        float opacity,
+        Gfx::Size base_size,
+        Gfx::Size size_increment,
+        i32 type,
+        String title,
+        i32 parent_window_id) => (i32 window_id)
+
+    DestroyWindow(i32 window_id) => (Vector<i32> destroyed_window_ids)
+
+    SetWindowTitle(i32 window_id, String title) => ()
+    GetWindowTitle(i32 window_id) => (String title)
+
+    SetWindowRect(i32 window_id, Gfx::Rect rect) => (Gfx::Rect rect)
+    GetWindowRect(i32 window_id) => (Gfx::Rect rect)
+
+    InvalidateRect(i32 window_id, Vector<Gfx::Rect> rects, bool ignore_occlusion) =|
+    DidFinishPainting(i32 window_id, Vector<Gfx::Rect> rects) =|
+
+    SetGlobalCursorTracking(i32 window_id, bool enabled) => ()
+    SetWindowOpacity(i32 window_id, float opacity) => ()
+
+    SetWindowBackingStore(i32 window_id, i32 bpp, i32 pitch, i32 shbuf_id, bool has_alpha_channel, Gfx::Size size, bool flush_immediately) => ()
+    GetClipboardContents() => (i32 shbuf_id, i32 content_size, String content_type)
+    SetClipboardContents(i32 shbuf_id, i32 content_size, String content_type) => ()
+
+    WM_SetActiveWindow(i32 client_id, i32 window_id) =|
+    WM_SetWindowMinimized(i32 client_id, i32 window_id, bool minimized) =|
+    WM_StartWindowResize(i32 client_id, i32 window_id) =|
+    WM_PopupWindowMenu(i32 client_id, i32 window_id, Gfx::Point screen_position) =|
+    WM_SetWindowTaskbarRect(i32 client_id, i32 window_id, Gfx::Rect rect) =|
+
+    SetWindowHasAlphaChannel(i32 window_id, bool has_alpha_channel) => ()
+    MoveWindowToFront(i32 window_id) => ()
+    SetFullscreen(i32 window_id, bool fullscreen) => ()
+    PopupMenu(i32 menu_id, Gfx::Point screen_position) => ()
+    DismissMenu(i32 menu_id) => ()
+
+    AsyncSetWallpaper(String path) =|
+    
+    SetBackgroundColor(String background_color)  => ()
+    SetWallpaperMode(String mode)  => ()
+
+    SetResolution(Gfx::Size resolution) => (bool success, Gfx::Size resolution)
+    SetWindowIconBitmap(i32 window_id, Gfx::ShareableBitmap icon) => ()
+
+    GetWallpaper() => (String path)
+    SetWindowOverrideCursor(i32 window_id, i32 cursor_type) => ()
+
+    StartDrag(String text, String data_type, String data, i32 bitmap_id, Gfx::Size bitmap_size) => (bool started)
+
+    SetSystemTheme(String theme_path, String theme_name) => (bool success)
+    GetSystemTheme() => (String theme_name)
+
+    SetWindowBaseSizeAndSizeIncrement(i32 window_id, Gfx::Size base_size, Gfx::Size size_increment) => ()
+
+    EnableDisplayLink() =|
+    DisableDisplayLink() =|
+}

Services/WindowServer/WindowSwitcher.cpp

@@ -0,0 +1,256 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/StylePainter.h>
+#include <WindowServer/Event.h>
+#include <WindowServer/Screen.h>
+#include <WindowServer/WindowManager.h>
+#include <WindowServer/WindowSwitcher.h>
+
+namespace WindowServer {
+
+static WindowSwitcher* s_the;
+
+WindowSwitcher& WindowSwitcher::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
+WindowSwitcher::WindowSwitcher()
+{
+    s_the = this;
+}
+
+WindowSwitcher::~WindowSwitcher()
+{
+}
+
+void WindowSwitcher::set_visible(bool visible)
+{
+    if (m_visible == visible)
+        return;
+    m_visible = visible;
+    WindowManager::the().recompute_occlusions();
+    if (m_switcher_window)
+        m_switcher_window->set_visible(visible);
+    if (!m_visible)
+        return;
+    refresh();
+}
+
+Window* WindowSwitcher::selected_window()
+{
+    if (m_selected_index < 0 || m_selected_index >= static_cast<int>(m_windows.size()))
+        return nullptr;
+    return m_windows[m_selected_index].ptr();
+}
+
+void WindowSwitcher::event(Core::Event& event)
+{
+    if (!static_cast<Event&>(event).is_mouse_event())
+        return;
+
+    auto& mouse_event = static_cast<MouseEvent&>(event);
+    int new_hovered_index = -1;
+    for (size_t i = 0; i < m_windows.size(); ++i) {
+        auto item_rect = this->item_rect(i);
+        if (item_rect.contains(mouse_event.position())) {
+            new_hovered_index = i;
+            break;
+        }
+    }
+
+    if (mouse_event.type() == Event::MouseMove) {
+        if (m_hovered_index != new_hovered_index) {
+            m_hovered_index = new_hovered_index;
+            redraw();
+        }
+    }
+
+    if (new_hovered_index == -1)
+        return;
+
+    if (mouse_event.type() == Event::MouseDown)
+        select_window_at_index(new_hovered_index);
+
+    event.accept();
+}
+
+void WindowSwitcher::on_key_event(const KeyEvent& event)
+{
+    if (event.type() == Event::KeyUp) {
+        if (event.key() == Key_Logo) {
+            if (auto* window = selected_window()) {
+                window->set_minimized(false);
+                WindowManager::the().move_to_front_and_make_active(*window);
+            }
+            WindowManager::the().set_highlight_window(nullptr);
+            hide();
+        }
+        return;
+    }
+
+    if (event.key() == Key_LeftShift || event.key() == Key_RightShift)
+        return;
+    if (event.key() != Key_Tab) {
+        WindowManager::the().set_highlight_window(nullptr);
+        hide();
+        return;
+    }
+    ASSERT(!m_windows.is_empty());
+
+    int new_selected_index;
+
+    if (!event.shift()) {
+        new_selected_index = (m_selected_index + 1) % static_cast<int>(m_windows.size());
+    } else {
+        new_selected_index = (m_selected_index - 1) % static_cast<int>(m_windows.size());
+        if (new_selected_index < 0)
+            new_selected_index = static_cast<int>(m_windows.size()) - 1;
+    }
+    ASSERT(new_selected_index < static_cast<int>(m_windows.size()));
+
+    select_window_at_index(new_selected_index);
+}
+
+void WindowSwitcher::select_window(Window& window)
+{
+    for (size_t i = 0; i < m_windows.size(); ++i) {
+        if (m_windows.at(i) == &window) {
+            select_window_at_index(i);
+            return;
+        }
+    }
+}
+
+void WindowSwitcher::select_window_at_index(int index)
+{
+    m_selected_index = index;
+    auto* highlight_window = m_windows.at(index).ptr();
+    ASSERT(highlight_window);
+    WindowManager::the().set_highlight_window(highlight_window);
+    redraw();
+}
+
+void WindowSwitcher::redraw()
+{
+    draw();
+    WindowManager::the().invalidate(m_rect);
+}
+
+Gfx::Rect WindowSwitcher::item_rect(int index) const
+{
+    return {
+        padding(),
+        padding() + index * item_height(),
+        m_rect.width() - padding() * 2,
+        item_height()
+    };
+}
+
+void WindowSwitcher::draw()
+{
+    auto palette = WindowManager::the().palette();
+    Gfx::Painter painter(*m_switcher_window->backing_store());
+    painter.fill_rect({ {}, m_rect.size() }, palette.window());
+    painter.draw_rect({ {}, m_rect.size() }, palette.threed_shadow2());
+    for (size_t index = 0; index < m_windows.size(); ++index) {
+        auto& window = *m_windows.at(index);
+        auto item_rect = this->item_rect(index);
+        Color text_color;
+        Color rect_text_color;
+        if (static_cast<int>(index) == m_selected_index) {
+            painter.fill_rect(item_rect, palette.selection());
+            text_color = palette.selection_text();
+            rect_text_color = palette.threed_shadow1();
+        } else {
+            if (static_cast<int>(index) == m_hovered_index)
+                Gfx::StylePainter::paint_button(painter, item_rect, palette, Gfx::ButtonStyle::CoolBar, false, true);
+            text_color = palette.window_text();
+            rect_text_color = palette.threed_shadow2();
+        }
+        item_rect.shrink(item_padding(), 0);
+        Gfx::Rect thumbnail_rect = { item_rect.location().translated(0, 5), { thumbnail_width(), thumbnail_height() } };
+        if (window.backing_store()) {
+            painter.draw_scaled_bitmap(thumbnail_rect, *window.backing_store(), window.backing_store()->rect());
+            Gfx::StylePainter::paint_frame(painter, thumbnail_rect.inflated(4, 4), palette, Gfx::FrameShape::Container, Gfx::FrameShadow::Sunken, 2);
+        }
+        Gfx::Rect icon_rect = { thumbnail_rect.bottom_right().translated(-window.icon().width(), -window.icon().height()), { window.icon().width(), window.icon().height() } };
+        painter.fill_rect(icon_rect, palette.window());
+        painter.blit(icon_rect.location(), window.icon(), window.icon().rect());
+        painter.draw_text(item_rect.translated(thumbnail_width() + 12, 0), window.title(), WindowManager::the().window_title_font(), Gfx::TextAlignment::CenterLeft, text_color);
+        painter.draw_text(item_rect, window.rect().to_string(), Gfx::TextAlignment::CenterRight, rect_text_color);
+    }
+}
+
+void WindowSwitcher::refresh()
+{
+    auto& wm = WindowManager::the();
+    Window* selected_window = nullptr;
+    if (m_selected_index > 0 && m_windows[m_selected_index])
+        selected_window = m_windows[m_selected_index].ptr();
+    if (!selected_window)
+        selected_window = wm.highlight_window() ? wm.highlight_window() : wm.active_window();
+    m_windows.clear();
+    m_selected_index = 0;
+    int window_count = 0;
+    int longest_title_width = 0;
+    wm.for_each_window_of_type_from_front_to_back(
+        WindowType::Normal, [&](Window& window) {
+            if (window.is_frameless())
+                return IterationDecision::Continue;
+            ++window_count;
+            longest_title_width = max(longest_title_width, wm.font().width(window.title()));
+            if (selected_window == &window)
+                m_selected_index = m_windows.size();
+            m_windows.append(window.make_weak_ptr());
+            return IterationDecision::Continue;
+        },
+        true);
+    if (m_windows.is_empty()) {
+        hide();
+        return;
+    }
+    int space_for_window_rect = 180;
+    m_rect.set_width(thumbnail_width() + longest_title_width + space_for_window_rect + padding() * 2 + item_padding() * 2);
+    m_rect.set_height(window_count * item_height() + padding() * 2);
+    m_rect.center_within(Screen::the().rect());
+    if (!m_switcher_window)
+        m_switcher_window = Window::construct(*this, WindowType::WindowSwitcher);
+    m_switcher_window->set_rect(m_rect);
+    redraw();
+}
+
+void WindowSwitcher::refresh_if_needed()
+{
+    if (m_visible)
+        refresh();
+}
+
+}

Services/WindowServer/WindowSwitcher.h

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Vector.h>
+#include <AK/WeakPtr.h>
+#include <LibCore/Object.h>
+#include <LibGfx/Forward.h>
+#include <LibGfx/Rect.h>
+
+namespace WindowServer {
+
+class KeyEvent;
+class Window;
+
+class WindowSwitcher final : public Core::Object {
+    C_OBJECT(WindowSwitcher)
+public:
+    static WindowSwitcher& the();
+
+    WindowSwitcher();
+    virtual ~WindowSwitcher() override;
+
+    bool is_visible() const { return m_visible; }
+    void set_visible(bool);
+
+    void show() { set_visible(true); }
+    void hide() { set_visible(false); }
+
+    void on_key_event(const KeyEvent&);
+
+    void refresh();
+    void refresh_if_needed();
+
+    void select_window(Window&);
+
+private:
+    int thumbnail_width() const { return 40; }
+    int thumbnail_height() const { return 40; }
+    int item_height() const { return 10 + thumbnail_height(); }
+    int padding() const { return 8; }
+    int item_padding() const { return 8; }
+
+    void draw();
+    void redraw();
+    void select_window_at_index(int index);
+    Gfx::Rect item_rect(int index) const;
+    Window* selected_window();
+
+    virtual void event(Core::Event&) override;
+
+    RefPtr<Window> m_switcher_window;
+    Gfx::Rect m_rect;
+    bool m_visible { false };
+    Vector<WeakPtr<Window>> m_windows;
+    int m_selected_index { 0 };
+    int m_hovered_index { -1 };
+};
+
+}

Services/WindowServer/WindowType.h

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+// Keep this in sync with GUI::WindowType.
+enum class WindowType {
+    Invalid = 0,
+    Normal,
+    Menu,
+    WindowSwitcher,
+    Taskbar,
+    Tooltip,
+    Menubar,
+    MenuApplet,
+    Notification,
+    Desktop,
+};

Services/WindowServer/main.cpp

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "AppletManager.h"
+#include "Compositor.h"
+#include "EventLoop.h"
+#include "Screen.h"
+#include "WindowManager.h"
+#include <AK/SharedBuffer.h>
+#include <LibCore/ConfigFile.h>
+#include <LibGfx/Palette.h>
+#include <LibGfx/SystemTheme.h>
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+
+int main(int, char**)
+{
+    if (pledge("stdio video thread shared_buffer accept rpath wpath cpath unix proc fattr", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    if (unveil("/res", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil("/tmp", "cw") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil("/etc/WindowServer/WindowServer.ini", "rwc") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil("/dev", "rw") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    struct sigaction act;
+    memset(&act, 0, sizeof(act));
+    act.sa_flags = SA_NOCLDWAIT;
+    act.sa_handler = SIG_IGN;
+    int rc = sigaction(SIGCHLD, &act, nullptr);
+    if (rc < 0) {
+        perror("sigaction");
+        return 1;
+    }
+
+    auto wm_config = Core::ConfigFile::open("/etc/WindowServer/WindowServer.ini");
+    auto theme_name = wm_config->read_entry("Theme", "Name", "Default");
+
+    auto theme = Gfx::load_system_theme(String::format("/res/themes/%s.ini", theme_name.characters()));
+    ASSERT(theme);
+    Gfx::set_system_theme(*theme);
+    auto palette = Gfx::PaletteImpl::create_with_shared_buffer(*theme);
+
+    WindowServer::EventLoop loop;
+
+    if (pledge("stdio video thread shared_buffer accept rpath wpath cpath proc", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    WindowServer::Screen screen(wm_config->read_num_entry("Screen", "Width", 1024),
+        wm_config->read_num_entry("Screen", "Height", 768));
+    WindowServer::Compositor::the();
+    auto wm = WindowServer::WindowManager::construct(*palette);
+    auto am = WindowServer::AppletManager::construct();
+    auto mm = WindowServer::MenuManager::construct();
+
+    if (unveil("/tmp", "") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil("/dev", "") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil(nullptr, nullptr) < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    dbgprintf("Entering WindowServer main loop.\n");
+    loop.exec();
+    ASSERT_NOT_REACHED();
+}