Pass creation of Shadow sub class instance to Scene

Instead of having the Shadow factory method check the compositor type and
do the decision which Shadow sub class to create, a pure virtual method in
Scene is called which returns the specific Shadow sub class instance.

scene.h

@@ -72,6 +72,15 @@ public:
      * @param frame The EffectFrame this Scene::EffectFrame belongs to.
      */
     virtual Scene::EffectFrame *createEffectFrame(EffectFrameImpl *frame) = 0;
+    /**
+     * @brief Creates the Scene specific Shadow subclass.
+     *
+     * An implementing class has to create a proper instance. It is not allowed to
+     * return @c null.
+     *
+     * @param toplevel The Toplevel for which the Shadow needs to be created.
+     */
+    virtual Shadow *createShadow(Toplevel *toplevel) = 0;
     /**
      * Method invoked when the screen geometry is changed.
      * Reimplementing classes should also invoke the parent method

scene_opengl.cpp

@@ -641,6 +641,11 @@ Scene::EffectFrame *SceneOpenGL::createEffectFrame(EffectFrameImpl *frame)
     return new SceneOpenGL::EffectFrame(frame, this);
 }
 
+Shadow *SceneOpenGL::createShadow(Toplevel *toplevel)
+{
+    return new SceneOpenGLShadow(toplevel);
+}
+
 //****************************************
 // SceneOpenGL2
 //****************************************

scene_opengl.h

@@ -51,6 +51,7 @@ public:
     virtual void windowAdded(Toplevel*);
     virtual void windowDeleted(Deleted*);
     virtual Scene::EffectFrame *createEffectFrame(EffectFrameImpl *frame);
+    virtual Shadow *createShadow(Toplevel *toplevel);
     virtual void screenGeometryChanged(const QSize &size);
     virtual OverlayWindow *overlayWindow();
     virtual bool blocksForRetrace() const;

scene_xrender.cpp

@@ -293,6 +293,11 @@ Scene::EffectFrame *SceneXrender::createEffectFrame(EffectFrameImpl *frame)
     return new SceneXrender::EffectFrame(frame);
 }
 
+Shadow *SceneXrender::createShadow(Toplevel *toplevel)
+{
+    return new SceneXRenderShadow(toplevel);
+}
+
 //****************************************
 // SceneXrender::Window
 //****************************************

scene_xrender.h

@@ -46,6 +46,7 @@ public:
     virtual void windowAdded(Toplevel*);
     virtual void windowDeleted(Deleted*);
     virtual Scene::EffectFrame *createEffectFrame(EffectFrameImpl *frame);
+    virtual Shadow *createShadow(Toplevel *toplevel);
     virtual void screenGeometryChanged(const QSize &size);
     xcb_render_picture_t bufferPicture();
     virtual OverlayWindow *overlayWindow() {

shadow.cpp

@@ -20,12 +20,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "shadow.h"
 // kwin
 #include "atoms.h"
+#include "composite.h"
 #include "effects.h"
 #include "toplevel.h"
-#include "scene_opengl.h"
-#ifdef KWIN_HAVE_XRENDER_COMPOSITING
-#include "scene_xrender.h"
-#endif
 
 namespace KWin
 {
@@ -48,23 +45,14 @@ Shadow *Shadow::createShadow(Toplevel *toplevel)
     }
     auto data = Shadow::readX11ShadowProperty(toplevel->window());
     if (!data.isEmpty()) {
-        Shadow *shadow = NULL;
-        if (effects->isOpenGLCompositing()) {
-            shadow = new SceneOpenGLShadow(toplevel);
-        } else if (effects->compositingType() == XRenderCompositing) {
-#ifdef KWIN_HAVE_XRENDER_COMPOSITING
-            shadow = new SceneXRenderShadow(toplevel);
-#endif
-        }
+        Shadow *shadow = Compositor::self()->scene()->createShadow(toplevel);
 
-        if (shadow) {
-            if (!shadow->init(data)) {
-                delete shadow;
-                return NULL;
-            }
-            if (toplevel->effectWindow() && toplevel->effectWindow()->sceneWindow()) {
-                toplevel->effectWindow()->sceneWindow()->updateShadow(shadow);
-            }
+        if (!shadow->init(data)) {
+            delete shadow;
+            return NULL;
+        }
+        if (toplevel->effectWindow() && toplevel->effectWindow()->sceneWindow()) {
+            toplevel->effectWindow()->sceneWindow()->updateShadow(shadow);
         }
         return shadow;
     } else {