[SPv2] Decomposite otherwise-compositable animations that paint nothing.

third_party/WebKit/Source/core/animation/Animation.h

Index: third_party/WebKit/Source/core/animation/Animation.h
diff --git a/third_party/WebKit/Source/core/animation/Animation.h b/third_party/WebKit/Source/core/animation/Animation.h
index 6a0709a724b811192e4447ad3083df2512b889b2..96cc4f876fc3436099175720e010fef897796a74 100644
--- a/third_party/WebKit/Source/core/animation/Animation.h
+++ b/third_party/WebKit/Source/core/animation/Animation.h
@@ -31,6 +31,7 @@
 #ifndef Animation_h
 #define Animation_h
 
+#include <memory>

[pdr., 2017/03/16 21:20:04]

It took me a little while to page this back in. Can you add a summary to the
description?

The big points seem to be:
* In SPV1, layers are always created for composited animations so we are sure
the compositor gets the associated element id off the layer.
* In SPV2 we can optimize out even creating a paint chunk for opacity=0
animations, and the compositor never finds out about opacity=0 animations.
* This change ensures SPV2 only starts compositor animations with element ids
that were composited, effectively forcing non-composited animations back to the
main thread.

[wkorman, 2017/03/16 21:53:31]

Will do.
Rather than being about opacity = 0, this patch is aimed at the issue that, for
animated elements that paint no content at all, we never create a layer, thus
there is no layer to associated with a compositor element id in cc, and cc can't
run the composited animation.

The opacity = 0 issue you may be recalling is the one we addressed previously in
http://crrev.com/2652273004 but that case still involved elements that do
actually paint something (for example, they have a background with some color).
For elements that literally end up painting nothing at all because they have no
content, background or other painting-required style, we hit the case this bug
is about and this patch is trying to address.
Correct, I would rephrase the "element ids that were composited" bit slightly
for clarity. Something like, "...only starts compositor animations with element
ids for which we created a cc layer."

 #include "bindings/core/v8/ActiveScriptWrappable.h"
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ScriptPromise.h"
@@ -43,9 +44,9 @@
 #include "core/events/EventTarget.h"
 #include "platform/animation/CompositorAnimationDelegate.h"
 #include "platform/animation/CompositorAnimationPlayerClient.h"
+#include "platform/graphics/compositing/PaintArtifactCompositor.h"
 #include "platform/heap/Handle.h"
 #include "wtf/RefPtr.h"
-#include <memory>
 
 namespace blink {
 
@@ -149,9 +150,13 @@ class CORE_EXPORT Animation final : public EventTargetWithInlineData,
   void setOutdated();
   bool outdated() { return m_outdated; }
 
-  bool canStartAnimationOnCompositor() const;
-  bool isCandidateForAnimationOnCompositor() const;
-  bool maybeStartAnimationOnCompositor();
+  bool canStartAnimationOnCompositor(const Optional<CompositorElementIdSet>&
+                                         compositedAnimationElementIds) const;
+  bool isCandidateForAnimationOnCompositor(
+      const Optional<CompositorElementIdSet>& compositedAnimationElementIds)
+      const;
+  bool maybeStartAnimationOnCompositor(
+      const Optional<CompositorElementIdSet>& compositedAnimationElementIds);
   void cancelAnimationOnCompositor();
   void restartAnimationOnCompositor();
   void cancelIncompatibleAnimationsOnCompositor();
@@ -168,7 +173,9 @@ class CORE_EXPORT Animation final : public EventTargetWithInlineData,
 
   // Returns whether we should continue with the commit for this animation or
   // wait until next commit.
-  bool preCommit(int compositorGroup, bool startOnCompositor);
+  bool preCommit(int compositorGroup,
+                 const Optional<CompositorElementIdSet>&,
+                 bool startOnCompositor);
   void postCommit(double timelineTime);
 
   unsigned sequenceNumber() const { return m_sequenceNumber; }