Bug 1519934 - Remove useless nsDisplayTransform::mNoExtendContext. r=mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D16487

--HG--
extra : moz-landing-system : lando

layout/generic/nsFrame.cpp

@@ -2557,7 +2557,6 @@ static void WrapSeparatorTransform(nsDisplayListBuilder* aBuilder,
   nsDisplayTransform* item = MakeDisplayItem<nsDisplayTransform>(
       aBuilder, aFrame, aNonParticipants, aBuilder->GetVisibleRect(),
       Matrix4x4(), aIndex);
-  item->SetNoExtendContext();
 
   if (*aSeparator == nullptr) {
     *aSeparator = item;

layout/painting/nsDisplayList.cpp

@@ -7184,7 +7184,6 @@ nsDisplayTransform::nsDisplayTransform(
       mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot),
       mChildrenBuildingRect(aChildrenBuildingRect),
       mIndex(aIndex),
-      mNoExtendContext(false),
       mIsTransformSeparator(false),
       mTransformPreserves3DInited(false),
       mAllowAsyncAnimation(false) {
@@ -7248,7 +7247,6 @@ nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
       mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot),
       mChildrenBuildingRect(aChildrenBuildingRect),
       mIndex(aIndex),
-      mNoExtendContext(false),
       mIsTransformSeparator(false),
       mTransformPreserves3DInited(false),
       mAllowAsyncAnimation(aAllowAsyncAnimation) {
@@ -7272,7 +7270,6 @@ nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
       mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot),
       mChildrenBuildingRect(aChildrenBuildingRect),
       mIndex(aIndex),
-      mNoExtendContext(false),
       mIsTransformSeparator(true),
       mTransformPreserves3DInited(false),
       mAllowAsyncAnimation(false) {
@@ -7873,13 +7870,15 @@ bool nsDisplayTransform::CreateWebRenderCommands(
   bool animated =
       ActiveLayerTracker::IsStyleMaybeAnimated(Frame(), eCSSProperty_transform);
 
+  bool preserve3D = mFrame->Extend3DContext() && !mIsTransformSeparator;
+
   StackingContextHelper sc(
       aSc, GetActiveScrolledRoot(), mFrame, this, aBuilder, filters,
       LayoutDeviceRect(position, LayoutDeviceSize()), &newTransformMatrix,
       animationsId ? &prop : nullptr, nullptr, transformForSC, nullptr,
       gfx::CompositionOp::OP_OVER, !BackfaceIsHidden(),
-      mFrame->Extend3DContext() && !mNoExtendContext, deferredTransformItem,
-      wr::WrStackingContextClip::None(), animated);
+      preserve3D, deferredTransformItem, wr::WrStackingContextClip::None(),
+      animated);
 
   return mStoredList.CreateWebRenderCommands(aBuilder, aResources, sc, aManager,
                                              aDisplayListBuilder);
@@ -7932,8 +7931,8 @@ already_AddRefed<Layer> nsDisplayTransform::BuildLayer(
   }
 
   // Add the preserve-3d flag for this layer, BuildContainerLayerFor clears all
-  // flags, so we never need to explicitely unset this flag.
-  if (mFrame->Extend3DContext() && !mNoExtendContext) {
+  // flags, so we never need to explicitly unset this flag.
+  if (mFrame->Extend3DContext() && !mIsTransformSeparator) {
     container->SetContentFlags(container->GetContentFlags() |
                                Layer::CONTENT_EXTEND_3D_CONTEXT);
   } else {

layout/painting/nsDisplayList.h

@@ -6710,10 +6710,6 @@ class nsDisplayTransform : public nsDisplayHitTestInfoItem {
 
   void WriteDebugInfo(std::stringstream& aStream) override;
 
-  // Force the layer created for this item not to extend 3D context.
-  // See nsIFrame::BuildDisplayListForStackingContext()
-  void SetNoExtendContext() { mNoExtendContext = true; }
-
   void DoUpdateBoundsPreserves3D(nsDisplayListBuilder* aBuilder) override {
     MOZ_ASSERT(mFrame->Combines3DTransformWithAncestors() ||
                IsTransformSeparator());
@@ -6794,15 +6790,13 @@ class nsDisplayTransform : public nsDisplayHitTestInfoItem {
   mutable nsRect mBounds;
   // True for mBounds is valid.
   mutable bool mHasBounds;
-  // Be forced not to extend 3D context.  Since we don't create a
-  // transform item, a container layer, for every frames in a
-  // preserves3d context, the transform items of a child preserves3d
-  // context may extend the parent context not intented if the root of
-  // the child preserves3d context doesn't create a transform item.
-  // With this flags, we force the item not extending 3D context.
-  bool mNoExtendContext;
   // This item is a separator between 3D rendering contexts, and
   // mTransform have been presetted by the constructor.
+  // This also forces us not to extend the 3D context.  Since we don't create a
+  // transform item, a container layer, for every frame in a preserves3d
+  // context, the transform items of a child preserves3d context may extend the
+  // parent context unintendedly if the root of the child preserves3d context
+  // doesn't create a transform item.
   bool mIsTransformSeparator;
   // True if mTransformPreserves3D have been initialized.
   bool mTransformPreserves3DInited;