Make 'will-change: contents' suppress compositing in subtree

Source/core/rendering/compositing/CompositingReasonFinder.cpp

 // Copyright 2014 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 "config.h"
 #include "core/rendering/compositing/CompositingReasonFinder.h"
 
 #include "CSSPropertyNames.h"
 #include "HTMLNames.h"
 #include "core/frame/FrameView.h"
@@ skipping 92 matching lines @@
 
     if (requiresCompositingForTransform(renderer))
         directReasons |= CompositingReason3DTransform;
 
     if (requiresCompositingForFilters(renderer))
         directReasons |= CompositingReasonFilters;
 
     if (style->backfaceVisibility() == BackfaceVisibilityHidden)
         directReasons |= CompositingReasonBackfaceVisibilityHidden;
 
-    if (style->shouldCompositeForCurrentAnimations())
+    if (requiresCompositingForAnimation(renderer))

[abarth-chromium, 2014/06/06 17:18:29]

Why not pass in the RenderStyle given that these are style-determined reasons?

[ajuma, 2014/06/06 17:50:09]

Good point. CL up to fix this: https://codereview.chromium.org/317013005/

         directReasons |= CompositingReasonActiveAnimation;
 
-    if (style->hasWillChangeCompositingHint())
+    if (style->hasWillChangeCompositingHint() && !style->subtreeWillChangeContents())
         directReasons |= CompositingReasonWillChangeCompositingHint;
 
     ASSERT(!(directReasons & ~CompositingReasonComboAllStyleDeterminedReasons));
     return directReasons;
 }
 
 bool CompositingReasonFinder::requiresCompositingForTransform(RenderObject* renderer) const
 {
     // Note that we ask the renderer if it has a transform, because the style may have transforms,
     // but the renderer may be an inline that doesn't suppport them.
@@ skipping 32 matching lines @@
 
     if (requiresCompositingForPositionFixed(renderer, layer, 0))
         directReasons |= CompositingReasonPositionFixed;
 
     directReasons |= renderer->additionalCompositingReasons(m_compositingTriggers);
 
     ASSERT(!(directReasons & CompositingReasonComboAllStyleDeterminedReasons));
     return directReasons;
 }
 
+bool CompositingReasonFinder::requiresCompositingForAnimation(RenderObject* renderer) const
+{
+    if (renderer->style()->subtreeWillChangeContents())
+        return renderer->style()->isRunningAnimationOnCompositor();
+
+    return renderer->style()->shouldCompositeForCurrentAnimations();
+}
+
 bool CompositingReasonFinder::requiresCompositingForPosition(RenderObject* renderer, const RenderLayer* layer, RenderLayer::ViewportConstrainedNotCompositedReason* viewportConstrainedNotCompositedReason) const
 {
     return requiresCompositingForPositionSticky(renderer, layer) || requiresCompositingForPositionFixed(renderer, layer, viewportConstrainedNotCompositedReason);
 }
 
 bool CompositingReasonFinder::requiresCompositingForPositionSticky(RenderObject* renderer, const RenderLayer* layer) const
 {
     if (!(m_compositingTriggers & ViewportConstrainedPositionedTrigger))
         return false;
     if (renderer->style()->position() != StickyPosition)
@@ skipping 77 matching lines @@
             if (viewportConstrainedNotCompositedReason)
                 *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForBoundsOutOfView;
             return false;
         }
     }
 
     return true;
 }
 
 }