Rework the rendering model so that clients instantiate backing stores.

This makes interactive resizing work a lot better, althought it's still not
perfect. There are still glitches and unpleasant flashes of zeroed memory.

LibGUI/GEventLoop.cpp

@@ -78,8 +78,11 @@ int GEventLoop::exec()
     for (;;) {
         if (m_exit_requested)
             return m_exit_code;
-        if (m_queued_events.is_empty())
+        process_unprocessed_messages();
+        if (m_queued_events.is_empty()) {
             wait_for_event();
+            process_unprocessed_messages();
+        }
         Vector<QueuedEvent> events = move(m_queued_events);
         for (auto& queued_event : events) {
             auto* receiver = queued_event.receiver;
@@ -223,6 +226,7 @@ void GEventLoop::wait_for_event()
     struct timeval timeout = { 0, 0 };
     if (!m_timers.is_empty())
         get_next_timer_expiration(timeout);
+    ASSERT(m_unprocessed_messages.is_empty());
     int rc = select(max_fd + 1, &rfds, &wfds, nullptr, (m_queued_events.is_empty() && m_timers.is_empty()) ? nullptr : &timeout);
     if (rc < 0) {
         ASSERT_NOT_REACHED();
@@ -260,9 +264,16 @@ void GEventLoop::wait_for_event()
 
     bool success = drain_messages_from_server();
     ASSERT(success);
+}
 
+void GEventLoop::process_unprocessed_messages()
+{
     auto unprocessed_events = move(m_unprocessed_messages);
     for (auto& event : unprocessed_events) {
+        if (event.type == WSAPI_ServerMessage::Type::Greeting) {
+            m_server_pid = event.greeting.server_pid;
+            continue;
+        }
 
         if (event.type == WSAPI_ServerMessage::Error) {
             dbgprintf("GEventLoop got error message from server\n");
@@ -315,6 +326,9 @@ void GEventLoop::wait_for_event()
             break;
         }
     }
+
+    if (!m_unprocessed_messages.is_empty())
+        process_unprocessed_messages();
 }
 
 bool GEventLoop::drain_messages_from_server()

LibGUI/GEventLoop.h

@@ -39,9 +39,12 @@ public:
 
     WSAPI_ServerMessage sync_request(const WSAPI_ClientMessage& request, WSAPI_ServerMessage::Type response_type);
 
+    pid_t server_pid() const { return m_server_pid; }
+
 private:
     void wait_for_event();
     bool drain_messages_from_server();
+    void process_unprocessed_messages();
     void handle_paint_event(const WSAPI_ServerMessage&, GWindow&);
     void handle_resize_event(const WSAPI_ServerMessage&, GWindow&);
     void handle_mouse_event(const WSAPI_ServerMessage&, GWindow&);
@@ -64,8 +67,8 @@ private:
     bool m_running { false };
     bool m_exit_requested { false };
     int m_exit_code { 0 };
-
     int m_next_timer_id { 1 };
+    pid_t m_server_pid { 0 };
 
     struct EventLoopTimer {
         int timer_id { 0 };

LibGUI/GWidget.cpp

@@ -28,11 +28,14 @@ void GWidget::set_relative_rect(const Rect& rect)
 {
     if (rect == m_relative_rect)
         return;
-    if (m_relative_rect.size() != rect.size()) {
-        auto event = make<GResizeEvent>(m_relative_rect.size(), rect.size());
-        GEventLoop::main().post_event(this, move(event));
-    }
+    bool size_changed = m_relative_rect.size() != rect.size();
     m_relative_rect = rect;
+
+    if (size_changed) {
+        GResizeEvent resize_event(m_relative_rect.size(), rect.size());
+        event(resize_event);
+    }
+
     update();
 }
 

LibGUI/GWindow.cpp

@@ -169,9 +169,36 @@ void GWindow::event(GEvent& event)
             return;
         auto& paint_event = static_cast<GPaintEvent&>(event);
         auto rect = paint_event.rect();
-        if (rect.is_empty())
+        bool created_new_backing_store = !m_backing;
+        if (!m_backing) {
+            // NOTE: size() may change at any time since it's synchronously retrieved from the WindowServer.
+            ASSERT(GEventLoop::main().server_pid());
+            Size new_backing_store_size = size();
+            size_t size_in_bytes = new_backing_store_size.area() * sizeof(RGBA32);
+            void* buffer;
+            int shared_buffer_id = create_shared_buffer(GEventLoop::main().server_pid(), size_in_bytes, (void**)&buffer);
+            ASSERT(shared_buffer_id >= 0);
+            ASSERT(buffer);
+            ASSERT(buffer != (void*)-1);
+            m_backing = GraphicsBitmap::create_with_shared_buffer(
+                        m_has_alpha_channel ? GraphicsBitmap::Format::RGBA32 : GraphicsBitmap::Format::RGB32,
+                        shared_buffer_id,
+                        new_backing_store_size, (RGBA32*)buffer);
+        }
+        if (rect.is_empty() || created_new_backing_store)
             rect = m_main_widget->rect();
         m_main_widget->event(*make<GPaintEvent>(rect));
+        if (created_new_backing_store) {
+            WSAPI_ClientMessage message;
+            message.type = WSAPI_ClientMessage::Type::SetWindowBackingStore;
+            message.window_id = m_window_id;
+            message.backing.bpp = 32;
+            message.backing.pitch = m_backing->pitch();
+            message.backing.shared_buffer_id = m_backing->shared_buffer_id();
+            message.backing.has_alpha_channel = m_backing->has_alpha_channel();
+            message.backing.size = m_backing->size();
+            GEventLoop::main().post_message_to_server(message);
+        }
         if (m_window_id) {
             WSAPI_ClientMessage message;
             message.type = WSAPI_ClientMessage::Type::DidFinishPainting;
@@ -210,6 +237,7 @@ void GWindow::event(GEvent& event)
     }
 
     if (event.type() == GEvent::Resize) {
+        m_backing = nullptr;
         m_pending_paint_event_rects.clear();
         m_rect_when_windowless = { { }, static_cast<GResizeEvent&>(event).size() };
         m_main_widget->set_relative_rect({ { }, static_cast<GResizeEvent&>(event).size() });
@@ -233,7 +261,7 @@ void GWindow::update(const Rect& a_rect)
 #ifdef UPDATE_COALESCING_DEBUG
             dbgprintf("Ignoring %s since it's contained by pending rect %s\n", a_rect.to_string().characters(), pending_rect.to_string().characters());
 #endif
-            return;
+            //return;
         }
     }
     m_pending_paint_event_rects.append(a_rect);

LibGUI/GWindow.h

@@ -68,6 +68,8 @@ public:
     const GWidget* hovered_widget() const { return m_hovered_widget.ptr(); }
     void set_hovered_widget(GWidget*);
 
+    GraphicsBitmap* backing() { return m_backing.ptr(); }
+
 private:
     virtual const char* class_name() const override { return "GWindow"; }