Add static root property tree nodes [spv2]

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 0ce6ff6e4306a250840b5e70777ef9786ecd3089..e865b4025c9ebe78df5878752cef66db106e8c0b 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
@@ -20,28 +20,49 @@
 
 namespace blink {
 
-void PaintPropertyTreeBuilder::buildTreeRootNodes(FrameView& rootFrame, PaintPropertyTreeBuilderContext& context)
+namespace {
+    TransformPaintPropertyNode* rootTransformNode()
+    {
+        DEFINE_STATIC_REF(TransformPaintPropertyNode, rootTransform, (TransformPaintPropertyNode::create(nullptr, TransformationMatrix(), FloatPoint3D())));
+        return rootTransform;
+    }
+
+    ClipPaintPropertyNode* rootClipNode()
+    {
+        DEFINE_STATIC_REF(ClipPaintPropertyNode, rootClip, (ClipPaintPropertyNode::create(nullptr, rootTransformNode(), FloatRoundedRect(LayoutRect::infiniteIntRect()))));
+        return rootClip;
+    }
+
+    EffectPaintPropertyNode* rootEffectNode()
+    {
+        DEFINE_STATIC_REF(EffectPaintPropertyNode, rootEffect, (EffectPaintPropertyNode::create(nullptr, 1.0)));
+        return rootEffect;
+    }
+
+    ScrollPaintPropertyNode* rootScrollNode()
+    {
+        DEFINE_STATIC_REF(ScrollPaintPropertyNode, rootScroll, (ScrollPaintPropertyNode::create(nullptr, rootTransformNode(), IntSize(), IntSize(), false, false)));
+        return rootScroll;
+    }
+}
+
+PaintPropertyTreeBuilderContext PaintPropertyTreeBuilder::setupInitialContext()
 {
+    PaintPropertyTreeBuilderContext context;
+
+    // TODO(pdr): Update the root layer scrolling paths to use the static root nodes.
     if (RuntimeEnabledFeatures::rootLayerScrollingEnabled())
-        return;
+        return context;
 
-    if (!rootFrame.rootTransform() || rootFrame.rootTransform()->parent()) {
-        rootFrame.setRootTransform(TransformPaintPropertyNode::create(nullptr, TransformationMatrix(), FloatPoint3D()));
-        rootFrame.setRootClip(ClipPaintPropertyNode::create(nullptr, rootFrame.rootTransform(), FloatRoundedRect(LayoutRect::infiniteIntRect())));
-        rootFrame.setRootEffect(EffectPaintPropertyNode::create(nullptr, 1.0));
-        rootFrame.setRootScroll(ScrollPaintPropertyNode::create(nullptr, rootFrame.rootTransform(), IntSize(), IntSize(), false, false));
-    } else {
-        DCHECK(rootFrame.rootClip() && !rootFrame.rootClip()->parent());
-        DCHECK(rootFrame.rootEffect() && !rootFrame.rootEffect()->parent());
-        DCHECK(rootFrame.rootScroll() && !rootFrame.rootScroll()->parent());
-        // Ensure main thread scroll reasons are reset.
-        rootFrame.rootScroll()->update(nullptr, rootFrame.rootTransform(), IntSize(), IntSize(), false, false);
-    }
+    context.current.transform = context.absolutePosition.transform = context.fixedPosition.transform = rootTransformNode();
+    context.current.scroll = context.absolutePosition.scroll = context.fixedPosition.scroll = rootScrollNode();
+    context.current.clip = context.absolutePosition.clip = context.fixedPosition.clip = rootClipNode();
+    context.currentEffect = rootEffectNode();
+
+    // Ensure scroll tree properties are reset. They will be rebuilt during the tree walk.
+    rootScrollNode()->clearMainThreadScrollingReasons();

[jbroman, 2016/09/22 14:20:52]

This one confuses me a little. If there's a global root, presumably it should be
treated as immutable? Modifying it seems bad given that it's shared by several
FrameViews.

[pdr., 2016/09/22 19:48:20]

This patch was just matching the existing behavior here, this was previously
hidden in "rootFrame.rootScroll()->update(...)" but is now explicit. The reason
this occurs is we propagate the "has background attachment fixed" main thread
scroll reason all the way to the root, even though the root isn't used for
scrolling. We could change this to make the root nodes immutable
(dcheck(!isRoot() in all prop tree node update(...) functions), but I'd like to
defer that until the RLS and non-RLS codepaths both use these root nodes.

 
-    context.current.transform = context.absolutePosition.transform = context.fixedPosition.transform = rootFrame.rootTransform();
-    context.current.scroll = rootFrame.rootScroll();
-    context.current.clip = context.absolutePosition.clip = context.fixedPosition.clip = rootFrame.rootClip();
-    context.currentEffect = rootFrame.rootEffect();
+    return context;
 }
 
 void createOrUpdateFrameViewPreTranslation(FrameView& frameView,
@@ -156,6 +177,9 @@ void PaintPropertyTreeBuilder::buildTreeNodes(FrameView& frameView, PaintPropert
     context.fixedPosition = context.current;
     context.fixedPosition.transform = frameView.preTranslation();
     context.fixedPosition.scroll = initialScroll;
+
+    std::unique_ptr<PropertyTreeState> contentsState(new PropertyTreeState(context.current.transform, context.current.clip, context.currentEffect, context.current.scroll));
+    frameView.setTotalPropertyTreeStateForContents(std::move(contentsState));
 }
 
 void PaintPropertyTreeBuilder::updatePaintOffsetTranslation(const LayoutObject& object, PaintPropertyTreeBuilderContext& context)