--- a/Framework/Layers/LayerSourceBase.h	Tue May 16 22:12:41 2017 +0200
+++ b/Framework/Layers/LayerSourceBase.h	Wed May 17 22:03:09 2017 +0200
@@ -29,25 +29,37 @@
   {
   private:
     IObserver*  observer_;
+    bool        started_;
 
   protected:
+    bool IsStarted()
+    {
+      return started_;
+    }
+
+    void NotifyGeometryReady();
+    
     void NotifySourceChange();
 
     void NotifySliceChange(const SliceGeometry& slice);
 
     // Takes ownership of "layer" (that cannot be "NULL")
     void NotifyLayerReady(ILayerRenderer* layer,
-                          ILayerSource& source,
                           const SliceGeometry& viewportSlice);
     
-    void NotifyLayerError(ILayerSource& source,
-                          const SliceGeometry& viewportSlice);
+    void NotifyLayerError(const SliceGeometry& viewportSlice);
+
+    virtual void StartInternal() = 0;
 
   public:
-    LayerSourceBase() : observer_(NULL)
+    LayerSourceBase() :
+      observer_(NULL),
+      started_(false)
     {
     }
     
     virtual void SetObserver(IObserver& observer);
+
+    virtual void Start();
   };
 }