Bug 1234485 - Part 4. Implement nsDisplayMask::ShouldPaintOnMaskLayer. r=mstange

MozReview-Commit-ID: CChi1vbLLh8

--HG--
extra : rebase_source : d869aeb9993e6d631a494f0b63494de3b576b5b3

layout/base/nsDisplayList.cpp

@@ -7057,9 +7057,37 @@ nsDisplayMask::GetLayerState(nsDisplayListBuilder* aBuilder,
                              LayerManager* aManager,
                              const ContainerLayerParameters& aParameters)
 {
+  if (ShouldPaintOnMaskLayer(aManager)) {
+    return RequiredLayerStateForChildren(aBuilder, aManager, aParameters,
+                                         mList, GetAnimatedGeometryRoot());
+  }
+
   return LAYER_SVG_EFFECTS;
 }
 
+bool nsDisplayMask::ShouldPaintOnMaskLayer(LayerManager* aManager)
+{
+  if (!aManager->IsCompositingCheap()) {
+    return false;
+  }
+
+  nsSVGIntegrationUtils::MaskUsage maskUsage;
+  nsSVGIntegrationUtils::DetermineMaskUsage(mFrame, mHandleOpacity, maskUsage);
+
+  if (!maskUsage.shouldGenerateMaskLayer ||
+      maskUsage.opacity != 1.0 || maskUsage.shouldApplyClipPath ||
+      maskUsage.shouldApplyBasicShape ||
+      maskUsage.shouldGenerateClipMaskLayer) {
+    return false;
+  }
+
+  if (!nsSVGIntegrationUtils::IsMaskResourceReady(mFrame)) {
+    return false;
+  }
+
+  return true;
+}
+
 bool nsDisplayMask::ComputeVisibility(nsDisplayListBuilder* aBuilder,
                                       nsRegion* aVisibleRegion)
 {

layout/base/nsDisplayList.h

@@ -3918,6 +3918,10 @@ public:
     return mDestRects;
   }
 private:
+  // According to mask property and the capability of aManager, determine
+  // whether paint mask onto a dedicate mask layer.
+  bool ShouldPaintOnMaskLayer(LayerManager* aManager);
+
   nsTArray<nsRect> mDestRects;
 };