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

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/layout/LayoutView.h"
 #include "core/paint/ObjectPaintProperties.h"
 #include "core/paint/PaintLayer.h"
@@ skipping 292 matching lines @@
         context.clipForOutOfFlowPositioned = context.currentClip;
     }
 
     if (createdNewTransform || object.isSVGRoot()) {
         context.transformForFixedPositioned = context.currentTransform;
         context.paintOffsetForFixedPositioned = context.paintOffset;
         context.clipForFixedPositioned = context.currentClip;
     }
 }
 
+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);
 
     deriveBorderBoxFromContainerContext(object, localContext);
     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
     RefPtr<TransformPaintPropertyNode> newTransformNodeForPerspective = createPerspectiveIfNeeded(object, localContext);
     RefPtr<TransformPaintPropertyNode> newTransformNodeForScrollTranslation = createScrollTranslationIfNeeded(object, localContext);
     updateOutOfFlowContext(object, newTransformNodeForTransform, localContext);
 
     if (newTransformNodeForPaintOffsetTranslation || newTransformNodeForTransform || newEffectNode || newClipNodeForOverflowClip || newTransformNodeForPerspective || newTransformNodeForScrollTranslation) {
         OwnPtr<ObjectPaintProperties> updatedPaintProperties = ObjectPaintProperties::create(
             newTransformNodeForPaintOffsetTranslation.release(),
             newTransformNodeForTransform.release(),
             newEffectNode.release(),
             newClipNodeForOverflowClip.release(),
             newTransformNodeForPerspective.release(),
             newTransformNodeForScrollTranslation.release());
         object.setObjectPaintProperties(updatedPaintProperties.release());
     } else {
         object.clearObjectPaintProperties();
     }
 
     for (LayoutObject* child = object.slowFirstChild(); child; child = child->nextSibling()) {
         if (child->isBoxModelObject() || child->isSVG())
             walk(*child, localContext);
     }
 }
 
 } // namespace blink