WindowServer: Give windows a "background color" to use for missing parts.

When resizing a window, we often end up having to paint some part of it
without coverage in the current backing store. This patch makes those cases
look nicer by having a fallback background color for each window, passed
along with the CreateWindow client message.

Applications/Terminal/main.cpp

@@ -88,6 +88,7 @@ int main(int argc, char** argv)
     make_shell(ptm_fd);
 
     auto* window = new GWindow;
+    window->set_background_color(Color::Black);
     window->set_double_buffering_enabled(false);
     window->set_should_exit_event_loop_on_close(true);
 

LibGUI/GWindow.cpp

@@ -62,6 +62,7 @@ void GWindow::show()
     request.window.modal = m_modal;
     request.window.resizable = m_resizable;
     request.window.opacity = m_opacity_when_windowless;
+    request.window.background_color = m_background_color.value();
     request.window.size_increment = m_size_increment;
     request.window.base_size = m_base_size;
     request.window.type = (WSAPI_WindowType)m_window_type;

LibGUI/GWindow.h

@@ -38,6 +38,9 @@ public:
     String title() const;
     void set_title(const String&);
 
+    Color background_color() const { return m_background_color; }
+    void set_background_color(Color color) { m_background_color = color; }
+
     int x() const { return rect().x(); }
     int y() const { return rect().y(); }
     int width() const { return rect().width(); }
@@ -123,6 +126,7 @@ private:
     Vector<Rect> m_pending_paint_event_rects;
     Size m_size_increment;
     Size m_base_size;
+    Color m_background_color { Color::LightGray };
     GWindowType m_window_type { GWindowType::Normal };
     bool m_is_active { false };
     bool m_should_exit_app_on_close { false };

Servers/WindowServer/WSAPITypes.h

@@ -221,6 +221,7 @@ struct WSAPI_ClientMessage {
             float opacity;
             WSAPI_Size base_size;
             WSAPI_Size size_increment;
+            WSAPI_Color background_color;
         } window;
         struct {
             WSAPI_Size size;

Servers/WindowServer/WSClientConnection.cpp

@@ -372,6 +372,7 @@ void WSClientConnection::handle_request(const WSAPICreateWindowRequest& request)
 {
     int window_id = m_next_window_id++;
     auto window = make<WSWindow>(*this, request.window_type(), window_id, request.is_modal());
+    window->set_background_color(request.background_color());
     window->set_has_alpha_channel(request.has_alpha_channel());
     window->set_resizable(request.is_resizable());
     window->set_title(request.title());

Servers/WindowServer/WSMessage.h

@@ -430,7 +430,7 @@ private:
 
 class WSAPICreateWindowRequest : public WSAPIClientRequest {
 public:
-    WSAPICreateWindowRequest(int client_id, const Rect& rect, const String& title, bool has_alpha_channel, bool modal, bool resizable, float opacity, const Size& base_size, const Size& size_increment, WSWindowType window_type)
+    WSAPICreateWindowRequest(int client_id, const Rect& rect, const String& title, bool has_alpha_channel, bool modal, bool resizable, float opacity, const Size& base_size, const Size& size_increment, WSWindowType window_type, Color background_color)
         : WSAPIClientRequest(WSMessage::APICreateWindowRequest, client_id)
         , m_rect(rect)
         , m_title(title)
@@ -441,6 +441,7 @@ public:
         , m_size_increment(size_increment)
         , m_base_size(base_size)
         , m_window_type(window_type)
+        , m_background_color(background_color)
     {
     }
 
@@ -453,6 +454,7 @@ public:
     Size size_increment() const { return m_size_increment; }
     Size base_size() const { return m_base_size; }
     WSWindowType window_type() const { return m_window_type; }
+    Color background_color() const { return m_background_color; }
 
 private:
     Rect m_rect;
@@ -464,6 +466,7 @@ private:
     Size m_size_increment;
     Size m_base_size;
     WSWindowType m_window_type;
+    Color m_background_color;
 };
 
 class WSAPIDestroyWindowRequest : public WSAPIClientRequest {

Servers/WindowServer/WSMessageLoop.cpp

@@ -303,7 +303,7 @@ void WSMessageLoop::on_receive_from_client(int client_id, const WSAPI_ClientMess
         break;
     case WSAPI_ClientMessage::Type::CreateWindow:
         ASSERT(message.text_length < (ssize_t)sizeof(message.text));
-        post_message(client, make<WSAPICreateWindowRequest>(client_id, message.window.rect, String(message.text, message.text_length), message.window.has_alpha_channel, message.window.modal, message.window.resizable, message.window.opacity, message.window.base_size, message.window.size_increment, from_api(message.window.type)));
+        post_message(client, make<WSAPICreateWindowRequest>(client_id, message.window.rect, String(message.text, message.text_length), message.window.has_alpha_channel, message.window.modal, message.window.resizable, message.window.opacity, message.window.base_size, message.window.size_increment, from_api(message.window.type), Color::from_rgba(message.window.background_color)));
         break;
     case WSAPI_ClientMessage::Type::DestroyWindow:
         post_message(client, make<WSAPIDestroyWindowRequest>(client_id, message.window_id));

Servers/WindowServer/WSWindow.h

@@ -19,6 +19,9 @@ public:
     WSWindow(WSMessageReceiver&, WSWindowType);
     virtual ~WSWindow() override;
 
+    Color background_color() const { return m_background_color; }
+    void set_background_color(Color color) { m_background_color = color; }
+
     bool is_minimized() const { return m_minimized; }
     void set_minimized(bool);
 
@@ -153,4 +156,5 @@ private:
     Retained<GraphicsBitmap> m_icon;
     RetainPtr<WSCursor> m_override_cursor;
     WSWindowFrame m_frame;
+    Color m_background_color { Color::LightGray };
 };

Servers/WindowServer/WSWindowManager.cpp

@@ -819,7 +819,20 @@ void WSWindowManager::compose()
             dirty_rect_in_window_coordinates.move_by(-window.position());
             auto dst = window.position();
             dst.move_by(dirty_rect_in_window_coordinates.location());
+
+            m_back_painter->fill_rect(window.rect(), window.background_color());
+
             m_back_painter->blit(dst, *backing_store, dirty_rect_in_window_coordinates, window.opacity());
+
+            if (backing_store->width() < window.width()) {
+                Rect right_fill_rect { window.x() + backing_store->width(), window.y(), window.width() - backing_store->width(), window.height() };
+                m_back_painter->fill_rect(right_fill_rect, window.background_color());
+            }
+
+            if (backing_store->height() < window.height()) {
+                Rect bottom_fill_rect { window.x(), window.y() + backing_store->height(), window.width(), window.height() - backing_store->height() };
+                m_back_painter->fill_rect(bottom_fill_rect, window.background_color());
+            }
         }
         return IterationDecision::Continue;
     });