Use same layout logic in animations for deciding whether an element can transform

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintPropertyTreeBuilder.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutInline.h"
@@ skipping 115 matching lines @@
         if (!transform.isIdentity()) {
             // The origin is included in the local transform, so leave origin empty.
             context.current.transform = object.getMutableForPainting().ensureObjectPaintProperties().createOrUpdateTransform(
                 context.current.transform, TransformationMatrix(transform), FloatPoint3D());
             context.current.renderingContextID = 0;
             context.current.shouldFlattenInheritedTransform = false;
             return;
         }
     } else {
         const ComputedStyle& style = object.styleRef();
-        if (object.isBox() && (style.hasTransform() || style.preserves3D())) {
+        if (object.canTransformOnCompositor() && (style.hasTransform() || style.preserves3D())) {

[trchen, 2016/08/09 21:57:13]

Hmm... Since you changed the semantics of the function to
canTransformOnCompositor(). I think we should leave it as-is (object.isBox())
for here and below.

FYI this class PaintPropertyTreeBuilder is for generating property trees for
SPv2, and the compositing architecture changed a lot in SPv2. Basically we
delayed compositing decision to a very late stage in the pipeline. The transform
nodes will be always generated, but whether layers need to be created are solely
on cc's discretion.

             TransformationMatrix matrix;
             style.applyTransform(matrix, toLayoutBox(object).size(), ComputedStyle::ExcludeTransformOrigin,
                 ComputedStyle::IncludeMotionPath, ComputedStyle::IncludeIndependentTransformProperties);
             FloatPoint3D origin = transformOrigin(toLayoutBox(object));
 
             unsigned renderingContextID = context.current.renderingContextID;
             unsigned renderingContextIDForChildren = 0;
             bool flattensInheritedTransform = context.current.shouldFlattenInheritedTransform;
             bool childrenFlattenInheritedTransform = true;
 
@@ skipping 121 matching lines @@
     const ComputedStyle& style = box.styleRef();
     FloatSize borderBoxSize(box.size());
     return FloatPoint(
         floatValueForLength(style.perspectiveOriginX(), borderBoxSize.width()),
         floatValueForLength(style.perspectiveOriginY(), borderBoxSize.height()));
 }
 
 void PaintPropertyTreeBuilder::updatePerspective(const LayoutObject& object, PaintPropertyTreeBuilderContext& context)
 {
     const ComputedStyle& style = object.styleRef();
-    if (!object.isBox() || !style.hasPerspective()) {
+    if (!object.canTransformOnCompositor() || !style.hasPerspective()) {
         if (ObjectPaintProperties* properties = object.getMutableForPainting().objectPaintProperties())
             properties->clearPerspective();
         return;
     }
 
     // The perspective node must not flatten (else nothing will get
     // perspective), but it should still extend the rendering context as most
     // transform nodes do.
     TransformationMatrix matrix = TransformationMatrix().applyPerspective(style.perspective());
     FloatPoint3D origin = perspectiveOrigin(toLayoutBox(object)) + toLayoutSize(context.current.paintOffset);
@@ skipping 142 matching lines @@
     updateLocalBorderBoxContext(object, context);
     updateScrollbarPaintOffset(object, context);
     updateOverflowClip(object, context);
     updatePerspective(object, context);
     updateSvgLocalToBorderBoxTransform(object, context);
     updateScrollTranslation(object, context);
     updateOutOfFlowContext(object, context);
 }
 
 } // namespace blink