WindowServer: Support windows with alpha channels. And per-WSWindow opacity.

This patch also adds a Format concept to GraphicsBitmap. For now there are
only two formats: RGB32 and RGBA32. Windows with alpha channel have their
backing stores created in the RGBA32 format.

Use this to make Terminal windows semi-transparent for that comfy rice look.
There is one problem here, in that window compositing overdraw incurs
multiple passes of blending of the same pixels. This leads to a mismatch in
opacity which is obviously not good. I will work on this in a later patch.

The alpha blending is currently straight C++. It should be relatively easy
to optimize this using SSE instructions.

For now I'm just happy with the cute effect. :^)

LibGUI/GButton.cpp

@@ -36,7 +36,7 @@ void GButton::paint_event(GPaintEvent&)
             icon_location.move_by(1, 1);
         }
         if (m_icon) {
-            painter.blit_with_alpha(icon_location, *m_icon, m_icon->rect());
+            painter.blit(icon_location, *m_icon, m_icon->rect());
             painter.draw_text(content_rect, caption(), TextAlignment::Center, Color::Black);
         } else {
             painter.draw_text(content_rect, caption(), TextAlignment::Center, Color::Black);

LibGUI/GLabel.cpp

@@ -31,7 +31,7 @@ void GLabel::paint_event(GPaintEvent&)
         painter.fill_rect({ 0, 0, width(), height() }, background_color());
     if (m_icon) {
         auto icon_location = rect().center().translated(-(m_icon->width() / 2), -(m_icon->height() / 2));
-        painter.blit_with_alpha(icon_location, *m_icon, m_icon->rect());
+        painter.blit(icon_location, *m_icon, m_icon->rect());
     }
     if (!text().is_empty())
         painter.draw_text({ 0, 0, width(), height() }, text(), m_text_alignment, foreground_color());

LibGUI/GWidget.h

@@ -128,8 +128,8 @@ private:
     OwnPtr<GLayout> m_layout;
 
     Rect m_relative_rect;
-    Color m_background_color { 0xffffff };
-    Color m_foreground_color { 0x000000 };
+    Color m_background_color;
+    Color m_foreground_color;
     RetainPtr<Font> m_font;
 
     SizePolicy m_horizontal_size_policy { SizePolicy::Fill };

LibGUI/GWindow.cpp

@@ -59,6 +59,8 @@ void GWindow::show()
     request.type = WSAPI_ClientMessage::Type::CreateWindow;
     request.window_id = m_window_id;
     request.window.rect = m_rect_when_windowless;
+    request.window.has_alpha_channel = m_has_alpha_channel;
+    request.window.opacity = m_opacity_when_windowless;
     ASSERT(m_title_when_windowless.length() < sizeof(request.text));
     strcpy(request.text, m_title_when_windowless.characters());
     request.text_length = m_title_when_windowless.length();
@@ -280,3 +282,22 @@ void GWindow::set_global_cursor_tracking_widget(GWidget* widget)
     //        Maybe there could be a response that includes the current cursor location as of enabling.
     GEventLoop::main().post_message_to_server(request);
 }
+
+void GWindow::set_has_alpha_channel(bool value)
+{
+    ASSERT(!m_window_id);
+    m_has_alpha_channel = value;
+}
+
+void GWindow::set_opacity(float opacity)
+{
+    m_opacity_when_windowless = opacity;
+    if (!m_window_id)
+        return;
+    WSAPI_ClientMessage request;
+    request.type = WSAPI_ClientMessage::Type::SetWindowOpacity;
+    request.window_id = m_window_id;
+    request.window.opacity = opacity;
+    m_opacity_when_windowless = opacity;
+    GEventLoop::main().post_message_to_server(request);
+}

LibGUI/GWindow.h

@@ -15,6 +15,9 @@ public:
 
     static GWindow* from_window_id(int);
 
+    void set_has_alpha_channel(bool);
+    void set_opacity(float);
+
     int window_id() const { return m_window_id; }
 
     String title() const;
@@ -66,13 +69,15 @@ private:
 
     RetainPtr<GraphicsBitmap> m_backing;
     int m_window_id { 0 };
-    bool m_is_active { false };
+    float m_opacity_when_windowless { 1.0f };
     GWidget* m_main_widget { nullptr };
     GWidget* m_focused_widget { nullptr };
     WeakPtr<GWidget> m_global_cursor_tracking_widget;
     Rect m_rect_when_windowless;
     String m_title_when_windowless;
     Vector<Rect> m_pending_paint_event_rects;
+    bool m_is_active { false };
     bool m_should_exit_app_on_close { false };
+    bool m_has_alpha_channel { false };
 };