Bug 1240073 - Use the transformed frame as the AGR for active transform so that FrameLayerBuilder knows that they can move independently. r=tnikkel

--HG--
extra : rebase_source : ef1193b1c1ae351b910e5e4dae308698e83482e5

layout/base/nsDisplayList.cpp

@@ -5050,6 +5050,8 @@ nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
   : nsDisplayItem(aBuilder, aFrame)
   , mStoredList(aBuilder, aFrame, aList)
   , mTransformGetter(aTransformGetter)
+  , mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot)
+  , mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot)
   , mChildrenVisibleRect(aChildrenVisibleRect)
   , mIndex(aIndex)
   , mNoExtendContext(false)
@@ -5064,7 +5066,6 @@ nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
 void
 nsDisplayTransform::SetReferenceFrameToAncestor(nsDisplayListBuilder* aBuilder)
 {
-  mAnimatedGeometryRootForChildren = mAnimatedGeometryRoot;
   if (mFrame == aBuilder->RootReferenceFrame()) {
     return;
   }
@@ -5086,7 +5087,15 @@ nsDisplayTransform::SetReferenceFrameToAncestor(nsDisplayListBuilder* aBuilder)
     // frame, which is our AGR, not the parent AGR.
     mAnimatedGeometryRoot = mAnimatedGeometryRootForChildren;
   } else if (mAnimatedGeometryRoot->mParentAGR) {
-    mAnimatedGeometryRoot = mAnimatedGeometryRoot->mParentAGR;
+    mAnimatedGeometryRootForScrollMetadata = mAnimatedGeometryRoot->mParentAGR;
+    if (!MayBeAnimated(aBuilder)) {
+      // If we're an animated transform then we want the same AGR as our children
+      // so that FrameLayerBuilder knows that this layer moves with the transform
+      // and won't compute occlusions. If we're not animated then use our parent
+      // AGR so that inactive transform layers can go in the same PaintedLayer as
+      // surrounding content.
+      mAnimatedGeometryRoot = mAnimatedGeometryRoot->mParentAGR;
+    }
   }
   mVisibleRect = aBuilder->GetDirtyRect() + mToReferenceFrame;
 }
@@ -5118,6 +5127,8 @@ nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
   : nsDisplayItem(aBuilder, aFrame)
   , mStoredList(aBuilder, aFrame, aList)
   , mTransformGetter(nullptr)
+  , mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot)
+  , mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot)
   , mChildrenVisibleRect(aChildrenVisibleRect)
   , mIndex(aIndex)
   , mNoExtendContext(false)
@@ -5138,6 +5149,8 @@ nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
   : nsDisplayItem(aBuilder, aFrame)
   , mStoredList(aBuilder, aFrame, aItem)
   , mTransformGetter(nullptr)
+  , mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot)
+  , mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot)
   , mChildrenVisibleRect(aChildrenVisibleRect)
   , mIndex(aIndex)
   , mNoExtendContext(false)
@@ -5159,6 +5172,8 @@ nsDisplayTransform::nsDisplayTransform(nsDisplayListBuilder* aBuilder,
   , mStoredList(aBuilder, aFrame, aList)
   , mTransform(aTransform)
   , mTransformGetter(nullptr)
+  , mAnimatedGeometryRootForChildren(mAnimatedGeometryRoot)
+  , mAnimatedGeometryRootForScrollMetadata(mAnimatedGeometryRoot)
   , mChildrenVisibleRect(aChildrenVisibleRect)
   , mIndex(aIndex)
   , mNoExtendContext(false)
@@ -5777,8 +5792,13 @@ already_AddRefed<Layer> nsDisplayTransform::BuildLayer(nsDisplayListBuilder *aBu
                                                            this, mFrame,
                                                            eCSSProperty_transform);
   if (ShouldPrerender(aBuilder)) {
-    container->SetUserData(nsIFrame::LayerIsPrerenderedDataKey(),
-                           /*the value is irrelevant*/nullptr);
+    if (MayBeAnimated(aBuilder)) {
+      // Only allow async updates to the transform if we're an animated layer, since that's what
+      // triggers us to set the correct AGR in the constructor and makes sure FrameLayerBuilder
+      // won't compute occlusions for this layer.
+      container->SetUserData(nsIFrame::LayerIsPrerenderedDataKey(),
+                             /*the value is irrelevant*/nullptr);
+    }
     container->SetContentFlags(container->GetContentFlags() | Layer::CONTENT_MAY_CHANGE_TRANSFORM);
   } else {
     container->RemoveUserData(nsIFrame::LayerIsPrerenderedDataKey());
@@ -5787,6 +5807,21 @@ already_AddRefed<Layer> nsDisplayTransform::BuildLayer(nsDisplayListBuilder *aBu
   return container.forget();
 }
 
+bool
+nsDisplayTransform::MayBeAnimated(nsDisplayListBuilder* aBuilder)
+{
+  // Here we check if the *post-transform* bounds of this item are big enough
+  // to justify an active layer.
+  if (ActiveLayerTracker::IsStyleAnimated(aBuilder, mFrame, eCSSProperty_transform) &&
+      !IsItemTooSmallForActiveLayer(this))
+    return true;
+  if (EffectCompositor::HasAnimationsForCompositor(mFrame,
+                                                   eCSSProperty_transform)) {
+    return true;
+  }
+  return false;
+}
+
 nsDisplayItem::LayerState
 nsDisplayTransform::GetLayerState(nsDisplayListBuilder* aBuilder,
                                   LayerManager* aManager,
@@ -5798,13 +5833,7 @@ nsDisplayTransform::GetLayerState(nsDisplayListBuilder* aBuilder,
       mIsTransformSeparator) {
     return LAYER_ACTIVE_FORCE;
   }
-  // Here we check if the *post-transform* bounds of this item are big enough
-  // to justify an active layer.
-  if (ActiveLayerTracker::IsStyleAnimated(aBuilder, mFrame, eCSSProperty_transform) &&
-      !IsItemTooSmallForActiveLayer(this))
-    return LAYER_ACTIVE;
-  if (EffectCompositor::HasAnimationsForCompositor(mFrame,
-                                                   eCSSProperty_transform)) {
+  if (MayBeAnimated(aBuilder)) {
     return LAYER_ACTIVE;
   }
 

layout/base/nsDisplayList.h

@@ -3956,6 +3956,10 @@ public:
     return nsDisplayItem::ReferenceFrameForChildren(); 
   }
 
+  AnimatedGeometryRoot* AnimatedGeometryRootForScrollMetadata() const override {
+    return mAnimatedGeometryRootForScrollMetadata;
+  }
+
   virtual const nsRect& GetVisibleRectForChildren() const override
   {
     return mChildrenVisibleRect;
@@ -4103,6 +4107,8 @@ public:
                                                 bool aLogAnimations = false);
   bool CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) override;
 
+  bool MayBeAnimated(nsDisplayListBuilder* aBuilder);
+
   /**
    * This will return if it's possible for this element to be prerendered.
    * This should never return false if we're going to prerender.
@@ -4192,6 +4198,7 @@ private:
   Matrix4x4 mTransformPreserves3D;
   ComputeTransformFunction mTransformGetter;
   AnimatedGeometryRoot* mAnimatedGeometryRootForChildren;
+  AnimatedGeometryRoot* mAnimatedGeometryRootForScrollMetadata;
   nsRect mChildrenVisibleRect;
   uint32_t mIndex;
   nsRect mBounds;