Moving global blackout factor into RenderEngine

Cleanup of Abuffer implementations

include/openspace/abuffer/abuffer.h

@@ -55,7 +55,7 @@ public:
 
 	ABuffer();
 	virtual ~ABuffer();
-	virtual void resolve();
+	virtual void resolve(float blackoutFactor);
     virtual bool initialize() = 0;
 	virtual bool reinitialize();
 

include/openspace/abuffer/abufferframebuffer.h

@@ -36,6 +36,8 @@ public:
     virtual ~ABufferFramebuffer();
     virtual bool initialize();
     
+    void resolve(float blackoutFactor);
+    
     virtual void clear();
     virtual void preRender();
     virtual void postRender();