Bug 1267438 - Support adding ancestor mask layers from places other than SetupScrollingMetadata. r=mstange

MozReview-Commit-ID: DwdbSRdEMEc

--HG--
extra : rebase_source : 703ff74d56cecf0546457ff8940265f97a3331cc
extra : source : 1c8e4840f8b40b7e02b9274e446e278e8c907053
extra : histedit_source : 6efd4834b4ec52a6d57a05bdd9529cf39a7669a4

gfx/layers/Layers.h

@@ -1088,7 +1088,7 @@ public:
 
   /**
    * CONSTRUCTION PHASE ONLY
-   * Add a FrameMetrics-associated mask layer.
+   * Add mask layers associated with LayerClips.
    */
   void SetAncestorMaskLayers(const nsTArray<RefPtr<Layer>>& aLayers) {
     if (aLayers != mAncestorMaskLayers) {
@@ -1098,6 +1098,15 @@ public:
     }
   }
 
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * Add a mask layer associated with a LayerClip.
+   */
+  void AddAncestorMaskLayer(const RefPtr<Layer>& aLayer) {
+    mAncestorMaskLayers.AppendElement(aLayer);
+    Mutated();
+  }
+
   /**
    * CONSTRUCTION PHASE ONLY
    * Tell this layer what its transform should be. The transformation
@@ -1352,6 +1361,9 @@ public:
   Layer* GetAncestorMaskLayerAt(size_t aIndex) const {
     return mAncestorMaskLayers.ElementAt(aIndex);
   }
+  const nsTArray<RefPtr<Layer>>& GetAllAncestorMaskLayers() const {
+    return mAncestorMaskLayers;
+  }
 
   bool HasMaskLayers() const {
     return GetMaskLayer() || mAncestorMaskLayers.Length() > 0;

layout/base/FrameLayerBuilder.cpp

@@ -2268,6 +2268,7 @@ ContainerState::RecyclePaintedLayer(PaintedLayer* aLayer,
   // Clear clip rect and mask layer so we don't accidentally stay clipped.
   // We will reapply any necessary clipping.
   aLayer->SetMaskLayer(nullptr);
+  aLayer->SetAncestorMaskLayers({});
   aLayer->ClearExtraDumpInfo();
 
   PaintedDisplayItemLayerUserData* data =
@@ -4715,8 +4716,11 @@ ContainerState::SetupScrollingMetadata(NewLayerEntry* aEntry)
     MOZ_ASSERT(!aEntry->mBaseScrollMetadata->HasMaskLayer());
   }
 
-  // Any extra mask layers we need to attach to FrameMetrics.
-  nsTArray<RefPtr<Layer>> maskLayers;
+  // Any extra mask layers we need to attach to ScrollMetadatas.
+  // The list may already contain an entry added for the layer's scrolled clip
+  // so add to it rather than overwriting it (we clear the list when recycling
+  // a layer).
+  nsTArray<RefPtr<Layer>> maskLayers(aEntry->mLayer->GetAllAncestorMaskLayers());
 
   for (const DisplayItemScrollClip* scrollClip = aEntry->mScrollClip;
        scrollClip && scrollClip != mContainerScrollClip;
@@ -5186,6 +5190,7 @@ FrameLayerBuilder::BuildContainerLayerFor(nsDisplayListBuilder* aBuilder,
                      "Wrong layer type");
         containerLayer = static_cast<ContainerLayer*>(oldLayer);
         containerLayer->SetMaskLayer(nullptr);
+        containerLayer->SetAncestorMaskLayers({});
       }
     }
   }