Output svg foreign object paint offset in paint properties

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 5c58aa44a1edfc27408f48239064e38e82799bcc..cb522c911eb76937b467e76e99ca7c33716a3930 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
@@ -218,8 +218,8 @@ static FloatPoint3D transformOrigin(const LayoutBox& box)
 void PaintPropertyTreeBuilder::updateTransform(const LayoutObject& object, PaintPropertyTreeBuilderContext& context)
 {
     if (object.isSVG() && !object.isSVGRoot()) {
-        // SVG does not use paint offset internally.
-        DCHECK(context.current.paintOffset == LayoutPoint());
+        // SVG (other than SVGForeign object) does not use paint offset internally.

[pdr., 2016/09/29 01:26:34]

I think LayoutSVGText uses this too (the comment in
LayoutSVGForeignObject::layout alerted me to this). No need to fix that now, but
can you add "TODO(wangxianzhu): Investigate whether LayoutSVGText should use
paint offset too."

Nit: "SVG (other than SVGForeignObject) does not use paint offset internally."

[Xianzhu, 2016/09/29 01:32:47]

Done.

[Xianzhu, 2016/09/29 02:57:40]

Just looked into LayoutSVGText and found that it's different from
LayoutSVGForeignObject. LayoutSVGText's offset is fully implemented in SVG
hierarchy, while LayoutSVGForeignObject's viewport offset is baked into its
LayoutBox::location(). This seems the reason that we must exclude
LayoutSVGForeignObject's viewport offset from its transform. Perhaps we can
change that to make all non-root SVG objects behave in the same way about
transforms and paint offsets. The FIXME at line 227 below should cover this.

+        DCHECK(object.isSVGForeignObject() || context.current.paintOffset == LayoutPoint());
 
         // FIXME(pdr): Check for the presence of a transform instead of the value. Checking for an
         // identity matrix will cause the property tree structure to change during animations if
@@ -541,7 +541,7 @@ static void deriveBorderBoxFromContainerContext(const LayoutObject& object, Pain
     default:
         ASSERT_NOT_REACHED();
     }
-    if (boxModelObject.isBox() && (!boxModelObject.isSVG() || boxModelObject.isSVGRoot())) {
+    if (boxModelObject.isBox() && (!boxModelObject.isSVG() || boxModelObject.isSVGRoot() || boxModelObject.isSVGForeignObject())) {
         // TODO(pdr): Several calls in this function walk back up the tree to calculate containers
         // (e.g., topLeftLocation, offsetForInFlowPosition*). The containing block and other
         // containers can be stored on PaintPropertyTreeBuilderContext instead of recomputing them.