Optimization: double vertex and index buffers usage during Stage.drawToBitmapData

starling/src/starling/core/Starling.as

@@ -52,6 +52,8 @@ package starling.core
     import starling.utils.VAlign;
     import starling.utils.execute;
 
+    use namespace starling_internal;
+
     /** Dispatched when a new render context is created. The 'data' property references the context. */
     [Event(name="context3DCreate", type="starling.events.Event")]
 
@@ -486,9 +488,27 @@ package starling.core
         /** Renders the complete display list. Before rendering, the context is cleared; afterwards,
          *  it is presented. This can be avoided by enabling <code>shareContext</code>.*/ 
         public function render():void
+        {
+            if (prerender())
+            {
+                if (!mShareContext)
+                    RenderSupport.clear(mStage.color, 1.0);
+
+                mStage.render(mSupport, 1.0);
+                mSupport.finishQuadBatch();
+
+                if (mStatsDisplay)
+                    mStatsDisplay.drawCount = mSupport.drawCount;
+
+                if (!mShareContext)
+                    mContext.present();
+            }
+        }
+
+        starling_internal function prerender():Boolean
         {
             if (!contextValid)
-                return;
+                return false;
 
             makeCurrent();
             updateViewPort();
@@ -509,17 +529,7 @@ package starling.core
                 mClippedViewPort.height / scaleY,
                 mStage.stageWidth, mStage.stageHeight, mStage.cameraPosition);
 
-            if (!mShareContext)
-                RenderSupport.clear(mStage.color, 1.0);
-
-            mStage.render(mSupport, 1.0);
-            mSupport.finishQuadBatch();
-
-            if (mStatsDisplay)
-                mStatsDisplay.drawCount = mSupport.drawCount;
-
-            if (!mShareContext)
-                mContext.present();
+            return true;
         }
 
         private function updateViewPort(forceUpdate:Boolean=false):void
@@ -1014,6 +1024,8 @@ package starling.core
             }
         }
 
+        starling_internal function get support():RenderSupport { return mSupport; }
+
         /** The Starling stage object, which is the root of the display tree that is rendered. */
         public function get stage():Stage { return mStage; }
 

starling/src/starling/display/Stage.as

@@ -123,23 +123,25 @@ package starling.display
         public function drawToBitmapData(destination:BitmapData=null,
                                          transparent:Boolean=true):BitmapData
         {
-            var support:RenderSupport = new RenderSupport();
             var star:Starling = Starling.current;
+            var prendered:Boolean = star.prerender();
 
             if (destination == null)
                 destination = new BitmapData(star.backBufferWidth, star.backBufferHeight, transparent);
 
-            support.renderTarget = null;
-            support.setProjectionMatrix(0, 0, mWidth, mHeight, mWidth, mHeight, cameraPosition);
-
-            if (transparent) support.clear();
-            else             support.clear(mColor, 1);
-
-            render(support, 1.0);
-            support.finishQuadBatch();
-
-            Starling.current.context.drawToBitmapData(destination);
-            Starling.current.context.present(); // required on some platforms to avoid flickering
+            if (prendered)
+            {
+                var support:RenderSupport = star.support;
+
+                if (transparent) support.clear();
+                else             support.clear(mColor, 1);
+
+                render(support, 1.0);
+                support.finishQuadBatch();
+
+                star.context.drawToBitmapData(destination);
+                star.context.present(); // required on some platforms to avoid flickering
+            }
 
             return destination;
         }