Bug 1043426: Avoid doing work for empty visible regions. r=mattwoodrow

gfx/layers/Layers.cpp

@@ -1013,7 +1013,7 @@ ContainerLayer::DefaultComputeEffectiveTransforms(const Matrix4x4& aTransformToS
     }
   }
 
-  mUseIntermediateSurface = useIntermediateSurface;
+  mUseIntermediateSurface = useIntermediateSurface && !GetEffectiveVisibleRegion().IsEmpty();
   if (useIntermediateSurface) {
     ComputeEffectiveTransformsForChildren(Matrix4x4::From2D(residual));
   } else {

gfx/layers/composite/ContainerLayerComposite.cpp

@@ -401,6 +401,7 @@ RenderLayers(ContainerT* aContainer,
   for (size_t i = 0u; i < aContainer->mPrepared->mLayers.Length(); i++) {
     PreparedLayer& preparedData = aContainer->mPrepared->mLayers[i];
     LayerComposite* layerToRender = preparedData.mLayer;
+
     nsIntRect clipRect = preparedData.mClipRect;
     if (layerToRender->HasLayerBeenComposited()) {
       // Composer2D will compose this layer so skip GPU composition
@@ -502,6 +503,11 @@ ContainerRender(ContainerT* aContainer,
                  LayerManagerComposite* aManager,
                  const nsIntRect& aClipRect)
 {
+  nsIntRect visibleRect = aContainer->GetEffectiveVisibleRegion().GetBounds();
+  if (visibleRect.IsEmpty()) {
+    return;
+  }
+
   MOZ_ASSERT(aContainer->mPrepared);
   if (aContainer->UseIntermediateSurface()) {
     RefPtr<CompositingRenderTarget> surface;
@@ -516,7 +522,6 @@ ContainerRender(ContainerT* aContainer,
 
     float opacity = aContainer->GetEffectiveOpacity();
 
-    nsIntRect visibleRect = aContainer->GetEffectiveVisibleRegion().GetBounds();
 #ifdef MOZ_DUMP_PAINTING
     if (gfxUtils::sDumpPainting) {
       RefPtr<gfx::DataSourceSurface> surf = surface->Dump(aManager->GetCompositor());

gfx/layers/composite/ThebesLayerComposite.cpp

@@ -108,6 +108,12 @@ ThebesLayerComposite::GetRenderState()
 void
 ThebesLayerComposite::RenderLayer(const nsIntRect& aClipRect)
 {
+  const nsIntRegion& visibleRegion = GetEffectiveVisibleRegion();
+
+  if (visibleRegion.IsEmpty()) {
+    return;
+  }
+
   if (!mBuffer || !mBuffer->IsAttached()) {
     return;
   }
@@ -133,8 +139,6 @@ ThebesLayerComposite::RenderLayer(const nsIntRect& aClipRect)
   LayerManagerComposite::AutoAddMaskEffect autoMaskEffect(mMaskLayer, effectChain);
   AddBlendModeEffect(effectChain);
 
-  const nsIntRegion& visibleRegion = GetEffectiveVisibleRegion();
-
   TiledLayerProperties tiledLayerProps;
   if (mRequiresTiledProperties) {
     tiledLayerProps.mVisibleRegion = visibleRegion;