WindowServer: Add a window switcher.

This needs some work on the window ordering and things like that, but it
works quite nicely as a starting point.

The keyboard shortcut is Logo+Tab. :^)

WindowServer/WSWindowSwitcher.cpp

@@ -0,0 +1,118 @@
+#include <WindowServer/WSWindowSwitcher.h>
+#include <WindowServer/WSWindowManager.h>
+#include <WindowServer/WSMessage.h>
+#include <SharedGraphics/Font.h>
+
+WSWindowSwitcher::WSWindowSwitcher()
+{
+}
+
+WSWindowSwitcher::~WSWindowSwitcher()
+{
+}
+
+void WSWindowSwitcher::set_visible(bool visible)
+{
+    if (m_visible == visible)
+        return;
+    m_visible = visible;
+    if (!m_visible) {
+        WSWindowManager::the().invalidate(m_rect);
+        return;
+    }
+    invalidate();
+}
+
+WSWindow* WSWindowSwitcher::selected_window()
+{
+    if (m_selected_index < 0 || m_selected_index >= m_windows.size())
+        return nullptr;
+    return m_windows[m_selected_index].ptr();
+}
+
+void WSWindowSwitcher::on_key_event(const WSKeyEvent& event)
+{
+    if (event.type() == WSMessage::KeyUp) {
+        if (event.key() == Key_Logo) {
+            if (auto* window = selected_window()) {
+                WSWindowManager::the().set_active_window(window);
+                WSWindowManager::the().move_to_front(*window);
+            }
+            WSWindowManager::the().set_highlight_window(nullptr);
+            hide();
+        }
+        return;
+    }
+    if (event.key() != Key_Tab) {
+        hide();
+        return;
+    }
+    ASSERT(!m_windows.is_empty());
+    m_selected_index = (m_selected_index + 1) % m_windows.size();
+    ASSERT(m_selected_index < m_windows.size());
+    auto* highlight_window = m_windows.at(m_selected_index).ptr();
+    ASSERT(highlight_window);
+    WSWindowManager::the().set_highlight_window(highlight_window);
+    WSWindowManager::the().invalidate(m_rect);
+}
+
+void WSWindowSwitcher::draw(Painter& painter)
+{
+    painter.translate(m_rect.location());
+    painter.fill_rect({ { }, m_rect.size() }, Color::LightGray);
+    painter.draw_rect({ { }, m_rect.size() }, Color::DarkGray);
+
+    for (int index = 0; index < m_windows.size(); ++index) {
+        auto& window = *m_windows.at(index);
+        Rect item_rect {
+            padding(),
+            padding() + index * item_height(),
+            m_rect.width() - padding() * 2,
+            item_height()
+        };
+        Color text_color;
+        Color rect_text_color;
+        if (index == m_selected_index) {
+            painter.fill_rect(item_rect, Color::from_rgb(0x84351a));
+            text_color = Color::White;
+            rect_text_color = Color::LightGray;
+        } else {
+            text_color = Color::Black;
+            rect_text_color = Color::DarkGray;
+        }
+
+        painter.set_font(Font::default_bold_font());
+        painter.draw_text(item_rect, window.title(), TextAlignment::CenterLeft, text_color);
+        painter.set_font(WSWindowManager::the().font());
+        painter.draw_text(item_rect, window.rect().to_string(), TextAlignment::CenterRight, rect_text_color);
+    }
+    painter.translate(-m_rect.x(), -m_rect.y());
+}
+
+void WSWindowSwitcher::invalidate()
+{
+    WSWindow* selected_window = nullptr;
+    if (m_selected_index > 0 && m_windows[m_selected_index])
+        selected_window = m_windows[m_selected_index].ptr();
+    m_windows.clear();
+    m_selected_index = 0;
+    int window_count = 0;
+    int longest_title = 0;
+    WSWindowManager::the().for_each_visible_window_of_type_from_back_to_front(WSWindowType::Normal, [&] (WSWindow& window) {
+        ++window_count;
+        longest_title = max(longest_title, window.title().length());
+        if (selected_window == &window)
+            m_selected_index = m_windows.size();
+        m_windows.append(window.make_weak_ptr());
+        return IterationDecision::Continue;
+    });
+    if (m_windows.is_empty()) {
+        hide();
+        return;
+    }
+    int space_for_window_rect = WSWindowManager::the().font().glyph_width() * 24;
+    m_rect.set_width(longest_title * WSWindowManager::the().font().glyph_width() + space_for_window_rect + padding() * 2);
+    m_rect.set_height(window_count * item_height() + padding() * 2);
+    m_rect.center_within(WSWindowManager::the().m_screen_rect);
+    WSWindowManager::the().invalidate(m_rect);
+}