4 files changed, 8 insertions, 4 deletions
diff --git a/FL/Fl_Double_Window.H b/FL/Fl_Double_Window.H
index e4ef883f5..46dd106f2 100644
--- a/FL/Fl_Double_Window.H
+++ b/FL/Fl_Double_Window.H
@@ -40,11 +40,11 @@
 class FL_EXPORT Fl_Double_Window : public Fl_Window {
 protected:
   void flush(int eraseoverlay);
+public:
   /**
-    Force double buffering, even if the OS already buffers windows
-    (overlays need that on MacOS and Windows2000)
+    Return non-null if this is an Fl_Overlay_Window object.
   */
-  char force_doublebuffering_;
+  virtual Fl_Double_Window *as_overlay_window() {return NULL; }
 public:
   void show();
   void show(int a, char **b) {Fl_Window::show(a,b);}
diff --git a/FL/Fl_Image_Surface.H b/FL/Fl_Image_Surface.H
index f556ed549..fa98a4bcd 100644
--- a/FL/Fl_Image_Surface.H
+++ b/FL/Fl_Image_Surface.H
@@ -53,7 +53,6 @@ class FL_EXPORT Fl_Image_Surface : public Fl_Widget_Surface {
 private:
   class Helper;
   Helper *platform_surface;
-  Fl_Offscreen offscreen();
 protected:
   void translate(int x, int y);
   void untranslate();
@@ -69,6 +68,7 @@ public:
   void origin(int x, int y);
   int printable_rect(int *w, int *h);
   Fl_Offscreen get_offscreen_before_delete();
+  Fl_Offscreen offscreen();
 };
 
 #endif // Fl_Image_Surface_H
diff --git a/FL/Fl_Overlay_Window.H b/FL/Fl_Overlay_Window.H
index de45b6c17..5114d3029 100644
--- a/FL/Fl_Overlay_Window.H
+++ b/FL/Fl_Overlay_Window.H
@@ -72,6 +72,7 @@ protected:
   Fl_Overlay_Window(int X, int Y, int W, int H, const char *l=0);
 public:
   void show(int a, char **b) {Fl_Double_Window::show(a,b);}
+  virtual Fl_Double_Window *as_overlay_window() {return this; }
 };
 
 #endif
diff --git a/FL/Fl_Window_Driver.H b/FL/Fl_Window_Driver.H
index dea792669..540b6971f 100644
--- a/FL/Fl_Window_Driver.H
+++ b/FL/Fl_Window_Driver.H
@@ -40,6 +40,9 @@ public:
   static Fl_Window_Driver *newWindowDriver(Fl_Window *);
 
   virtual void take_focus() { }
+  virtual int double_flush(int eraseoverlay);
+  virtual void destroy_double_buffer();
+  void draw() {w->draw();}
 };