Bug 1300338: Do not attempt to preserve layer content when we're going to override it in a blend operation anyway. r=jrmuizel

MozReview-Commit-ID: DIEyrK89jtd

gfx/2d/DrawTargetD2D1.cpp

@@ -1343,7 +1343,9 @@ DrawTargetD2D1::FinalizeDrawing(CompositionOp aOp, const Pattern &aPattern)
       return;
     }
 
-    RefPtr<ID2D1Image> tmpImage = GetImageForLayerContent();
+    // We don't need to preserve the current content of this layer as the output
+    // of the blend effect should completely replace it.
+    RefPtr<ID2D1Image> tmpImage = GetImageForLayerContent(false);
 
     blendEffect->SetInput(0, tmpImage);
     blendEffect->SetInput(1, source);
@@ -1432,7 +1434,7 @@ DrawTargetD2D1::GetDeviceSpaceClipRect(D2D1_RECT_F& aClipRect, bool& aIsPixelAli
 }
 
 already_AddRefed<ID2D1Image>
-DrawTargetD2D1::GetImageForLayerContent()
+DrawTargetD2D1::GetImageForLayerContent(bool aShouldPreserveContent)
 {
   if (!CurrentLayer().mCurrentList) {
     RefPtr<ID2D1Bitmap> tmpBitmap;
@@ -1469,9 +1471,11 @@ DrawTargetD2D1::GetImageForLayerContent()
     }
 
     DCCommandSink sink(mDC);
-    list->Stream(&sink);
 
-    PushAllClips();
+    if (aShouldPreserveContent) {
+      list->Stream(&sink);
+      PushAllClips();
+    }
 
     if (mDidComplexBlendWithListInList) {
       return tmpBitmap.forget();

gfx/2d/DrawTargetD2D1.h

@@ -186,7 +186,7 @@ private:
   void AddDependencyOnSource(SourceSurfaceD2D1* aSource);
 
   // Must be called with all clips popped and an identity matrix set.
-  already_AddRefed<ID2D1Image> GetImageForLayerContent();
+  already_AddRefed<ID2D1Image> GetImageForLayerContent(bool aShouldPreserveContent = true);
 
   ID2D1Image* CurrentTarget()
   {