diff --git a/scene.h b/scene.h
index 6b2eafcfac..11cb8db93f 100644
--- a/scene.h
+++ b/scene.h
@@ -23,12 +23,21 @@ class Scene
     public:
         Scene( Workspace* ws );
         virtual ~Scene();
+        // repaints the given screen areas, windows provides the stacking order
         virtual void paint( QRegion damage, ToplevelList windows ) = 0;
+        // shape/size of a window changed
         virtual void windowGeometryShapeChanged( Toplevel* );
+        // opacity of a window changed
         virtual void windowOpacityChanged( Toplevel* );
+        // a new window has been created
         virtual void windowAdded( Toplevel* );
+        // a window has been destroyed
         virtual void windowDeleted( Toplevel* );
+        // transforms the window areas to screen areas
         virtual void transformWindowDamage( Toplevel*, QRegion& ) const;
+        // updates cached window information after an effect changes
+        // transformation
+        // TODO - remove?
         virtual void updateTransformation( Toplevel* );
     protected:
         Workspace* wspace;
diff --git a/scene_opengl.cpp b/scene_opengl.cpp
index d75e31f1fd..aeca18091c 100644
--- a/scene_opengl.cpp
+++ b/scene_opengl.cpp
@@ -184,6 +184,26 @@ void SceneOpenGL::windowGeometryShapeChanged( Toplevel* c )
     w.discardTexture();
     }
 
+void SceneOpenGL::windowOpacityChanged( Toplevel* )
+    {
+#if 0 // not really needed, windows are painted on every repaint
+      // and opacity is used when applying texture, not when
+      // creating it
+    if( !windows.contains( c )) // this is ok, texture is created
+        return;                 // on demand
+    Window& w = windows[ c ];
+    w.discardPixmap();
+    w.discardTexture();
+#endif
+    }
+
+void SceneOpenGL::updateTransformation( Toplevel* c )
+    {
+    // TODO this is only used in effects to later update
+    // screen damage - since opengl doesn't use screen
+    // damage, just leave this empty
+    }
+
 SceneOpenGL::Window::Window( Toplevel* c )
     : toplevel( c )
     , glxpixmap( None )
diff --git a/scene_opengl.h b/scene_opengl.h
index 3431f32f0a..f8e91240c7 100644
--- a/scene_opengl.h
+++ b/scene_opengl.h
@@ -27,9 +27,13 @@ class SceneOpenGL
         SceneOpenGL( Workspace* ws );
         virtual ~SceneOpenGL();
         virtual void paint( QRegion damage, ToplevelList windows );
-        virtual void windowAdded( Toplevel* c );
-        virtual void windowDeleted( Toplevel* c );
-        virtual void windowGeometryShapeChanged( Toplevel* c );
+        virtual void windowGeometryShapeChanged( Toplevel* );
+        virtual void windowOpacityChanged( Toplevel* );
+        virtual void windowAdded( Toplevel* );
+        virtual void windowDeleted( Toplevel* );
+// screen damage is not used with opengl, it's completely repainted
+//         virtual void transformWindowDamage( Toplevel*, QRegion& ) const;
+        virtual void updateTransformation( Toplevel* );
     private:
         typedef GLuint Texture;
         GC gcroot;