Make class Scene inherit from QObject

The class Scene now inherits from QObject and has the Q_OBJECT macro. The inheriting classes SceneOpenGL and SceneXRender are provided with the Q_OBJECT macro. Now it is possible to use signals and slots and replace direct method calls.

scene.cpp

@@ -91,7 +91,8 @@ namespace KWin
 Scene* scene = 0;
 
 Scene::Scene(Workspace* ws)
-    : wspace(ws)
+    : QObject(ws)
+    , wspace(ws)
     , has_waitSync(false)
     , lanczos_filter(new LanczosFilter())
 {

scene.h

@@ -38,8 +38,9 @@ class LanczosFilter;
 class Shadow;
 
 // The base class for compositing backends.
-class Scene
+class Scene : public QObject
 {
+    Q_OBJECT
 public:
     Scene(Workspace* ws);
     virtual ~Scene() = 0;

scene_opengl.h

@@ -39,6 +39,7 @@ namespace KWin
 class SceneOpenGL
     : public Scene
 {
+    Q_OBJECT
 public:
     class EffectFrame;
     class Texture;

scene_xrender.h

@@ -37,6 +37,7 @@ namespace KWin
 class SceneXrender
     : public Scene
 {
+    Q_OBJECT
 public:
     class EffectFrame;
     SceneXrender(Workspace* ws);