Prep for image support in windows.

src/ui_elements/desktop_elements/Window.h

@@ -9,12 +9,15 @@ class PaintEvent;
 class MouseEvent;
 class KeyboardEvent;
 class VisualLayer;
+class Image;
 class IPlatformWindow;
 using IPlatformWindowPtr = std::unique_ptr<IPlatformWindow>;
 
 namespace mt
 {
 
+class Screen;
+
 class Window
 {
 
@@ -48,12 +51,23 @@ public:
 
     void SetPlatformWindow(IPlatformWindowPtr window);
 
+    Image* getBackingImage() const;
+
+    void map();
+
+    void show();
+
+    void doPaint(mt::Screen* screen);
+
+    void clear();
+
 private:
     int mHandle {-1};
     WidgetUPtr mWidget {nullptr};
     unsigned mWidth {800};
     unsigned mHeight {600};
     IPlatformWindowPtr mPlatformWindow {nullptr};
+    std::unique_ptr<Image> mBackingImage;
 };
 }