Refactor LayoutView paint offset updates out of FrameView update code

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 67837699cc16e9e0f1c8b8dc50b902ffb5d6c427..c6ff4b7aac6385b20cff5ce36e29d24d1233327d 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
@@ -102,33 +102,18 @@ void updateFrameViewScroll(
   }
 }
 
-void PaintPropertyTreeBuilder::updatePropertiesAndContext(
+void PaintPropertyTreeBuilder::updateFramePropertiesAndContext(
     FrameView& frameView,
     PaintPropertyTreeBuilderContext& context) {
   if (RuntimeEnabledFeatures::rootLayerScrollingEnabled()) {
-    LayoutView* layoutView = frameView.layoutView();
-    if (!layoutView)
-      return;
-
-    TransformationMatrix frameTranslate;
-    frameTranslate.translate(frameView.x() + layoutView->location().x() +
-                                 context.current.paintOffset.x(),
-                             frameView.y() + layoutView->location().y() +
-                                 context.current.paintOffset.y());
-    layoutView->getMutableForPainting()
-        .ensurePaintProperties()
-        .updatePaintOffsetTranslation(context.current.transform, frameTranslate,
-                                      FloatPoint3D());
-
-    const auto* properties = layoutView->paintProperties();
-    DCHECK(properties && properties->paintOffsetTranslation());
-    context.current.transform = properties->paintOffsetTranslation();
-    context.current.paintOffset = LayoutPoint();
+    // With RootLayerScrolling, the LayoutView (a LayoutObject) properties are
+    // updated like other objects (see updatePropertiesAndContextForSelf and
+    // updatePropertiesAndContextForChildren) instead of having LayoutView-
+    // specific property updates here.
     context.current.renderingContextID = 0;

[trchen, 2016/11/01 22:14:00]

Alternative idea:
Can we add
context.current.paintOffset.moveBy(frameView.location());

Then force usesPaintOffsetTranslation = true in updatePaintOffsetTranslation()
below? This way we won't need to special case for LayoutView. Don't worry about
the snapping differences. paintOffset are expected to be integer at this point.

[pdr., 2016/11/01 23:28:23]

Done.

     context.current.shouldFlattenInheritedTransform = true;
     context.absolutePosition = context.current;
-    context.containerForAbsolutePosition =
-        nullptr;  // This will get set in updateOutOfFlowContext().
+    context.containerForAbsolutePosition = nullptr;
     context.fixedPosition = context.current;
     return;
   }
@@ -197,12 +182,33 @@ void PaintPropertyTreeBuilder::updatePropertiesAndContext(
   frameView.setTotalPropertyTreeStateForContents(std::move(contentsState));
 }
 
+void PaintPropertyTreeBuilder::updateLayoutViewPaintOffsetTranslation(
+    const LayoutView& view,
+    PaintPropertyTreeBuilderContext& context) {

[trchen, 2016/11/01 22:14:00]

DCHECK(RuntimeEnabledFeatures::rootLayerScrollingEnabled());

[pdr., 2016/11/01 23:28:23]

Done

+  const auto* frameView = view.frameView();
+  TransformationMatrix translate;
+  translate.translate(
+      frameView->x() + view.location().x() + context.current.paintOffset.x(),
+      frameView->y() + view.location().y() + context.current.paintOffset.y());

[trchen, 2016/11/01 22:14:00]

deriveBorderBoxFromContainerContext() should have already accumulated
view.location() to context.current.paintOffset. I think we only need

translate.translate(
    frameView->x() + context.current.paintOffset.x(),
    frameView->y() + context.current.paintOffset.y());

[pdr., 2016/11/01 23:28:23]

Done.

+  view.getMutableForPainting()
+      .ensurePaintProperties()
+      .updatePaintOffsetTranslation(context.current.transform, translate,
+                                    FloatPoint3D());
+
+  const auto* properties = view.paintProperties();
+  DCHECK(properties && properties->paintOffsetTranslation());
+  context.current.transform = context.absolutePosition.transform =
+      context.fixedPosition.transform = properties->paintOffsetTranslation();
+  context.current.paintOffset = context.absolutePosition.paintOffset =
+      context.fixedPosition.paintOffset = LayoutPoint();
+}
+
 void PaintPropertyTreeBuilder::updatePaintOffsetTranslation(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
-  // LayoutView's paint offset is updated in the FrameView property update.
-  if (object.isLayoutView()) {
-    DCHECK(context.current.paintOffset == LayoutPoint());
+  if (RuntimeEnabledFeatures::rootLayerScrollingEnabled() &&
+      object.isLayoutView()) {
+    updateLayoutViewPaintOffsetTranslation(toLayoutView(object), context);
     return;
   }