[SPv2] Adds pre-computed paint property context to PaintLayer.

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

Index: third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
index f48b8772ce4a0e0500b69506c1569b7940b483ce..16016e3e345a7aa98143a15b2457d4b05ebfdbe8 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
@@ -310,6 +310,18 @@ static void updateOutOfFlowContext(const LayoutObject& object, bool createdNewTr
     }
 }
 
+void cachePropertyIfPaintLayerPresents(LayoutObject& object, const PaintPropertyTreeBuilderContext& context)

[pdr., 2016/02/02 06:18:20]

Nit: cachePropertyIfPaintLayerPresent (because "if present" is singular)

[trchen, 2016/02/02 21:48:53]

Acknowledged.

+{
+    if (!object.hasLayer())
+        return;
+    ASSERT(object.isBoxModelObject());
+    PaintLayerRareData::CachedSPv2PaintParameters &cachedParameters = toLayoutBoxModelObject(object).layer()->accessCachedSPv2PaintParameters();
+    cachedParameters.paintOffset = context.paintOffset;
+    cachedParameters.properties.transform = context.currentTransform;
+    cachedParameters.properties.clip = context.currentClip;
+    cachedParameters.properties.effect = context.currentEffect;
+}
+
 void PaintPropertyTreeBuilder::walk(LayoutObject& object, const PaintPropertyTreeBuilderContext& context)
 {
     PaintPropertyTreeBuilderContext localContext(context);
@@ -318,6 +330,7 @@ void PaintPropertyTreeBuilder::walk(LayoutObject& object, const PaintPropertyTre
     RefPtr<TransformPaintPropertyNode> newTransformNodeForPaintOffsetTranslation = createPaintOffsetTranslationIfNeeded(object, localContext);
     RefPtr<TransformPaintPropertyNode> newTransformNodeForTransform = createTransformIfNeeded(object, localContext);
     RefPtr<EffectPaintPropertyNode> newEffectNode = createEffectIfNeeded(object, localContext);
+    cachePropertyIfPaintLayerPresents(object, localContext);

[pdr., 2016/02/02 06:18:20]

I think what you're trying to do here is to store off the "paint property state
of the world" just before applying the overflow clip--is that correct?

Overflow clip doesn't affect transform though... why do we cache the transform
paint property instead of using
PaintLayer.layoutObject->objectPaintProperties().transform or
ClipPaintPropertyNode.localTransformSpace?

[trchen, 2016/02/02 21:48:53]

Essentially it is the state for painting the stacking context. Overflow clip
applies at the normal flow level, thus not cached here.

For example, if we have a stacking-context scroller:
<div style="overflow:scroll; position:relative; z-index:0;">
    Lorem ipsum
</div>

The box decoration is not scrolled, but is painted by this layer. That's why we
don't include overflow clip in the cache. "Lorem ipsum" will be painted by
normal flow, and the overflow clip will be applied by BoxClipper/BlockPainter in
my 5th CL.

The cache still serves a purpose though. Let's look at another example (extra
clip not in the painting ancestor):
<div style="overflow:scroll">
    <div style="overflow:scroll">
        <div style="position:relative; z-index:0;"></div>

The innermost div will be painted as a positive child (child stacking context)
of the root, thus the intermediate overflow clips won't be traversed during
paint. To avoid the need to look for non-stacking-context ancestor during paint,
it is useful to cache the paint property state in the layers.

And there is the opposite example (clip in painting ancestor doesn't apply):
<div style="opacity:0.5; overflow:scroll">
    <div style="position:absolute;">

Again, I don't think there is an easy way we can determine the clip node without
an ancestor walk.

     RefPtr<ClipPaintPropertyNode> newClipNodeForOverflowClip = createOverflowClipIfNeeded(object, localContext);

[pdr., 2016/02/02 06:18:20]

This creates clips for both border radius and overflow clip. Does this patch
need to consider the border radius clip created before overflow clip?

[trchen, 2016/02/02 21:48:53]

See comments above. Border radius clip on normal flow will be applied in my 5th
CL.

     // TODO(trchen): Insert flattening transform here, as specified by
     // http://www.w3.org/TR/css3-transforms/#transform-style-property