[CSS Exclusions] Zoom causes shape-inside to fail when shape-padding is specified

Source/core/rendering/ExclusionPolygon.cpp

Index: Source/core/rendering/ExclusionPolygon.cpp
diff --git a/Source/core/rendering/ExclusionPolygon.cpp b/Source/core/rendering/ExclusionPolygon.cpp
index 136287ac40f54a90d70754c8defa857add7cc4cd..63eae0140fc811fc9ff82855af9b4e63a1d5c32d 100644
--- a/Source/core/rendering/ExclusionPolygon.cpp
+++ b/Source/core/rendering/ExclusionPolygon.cpp
@@ -129,6 +129,12 @@ static inline void appendArc(Vector<FloatPoint>& vertices, const FloatPoint& arc
     vertices.append(endArcVertex);
 }
 
+static inline void snapVerticesToLayoutUnitGrid(Vector<FloatPoint>& vertices)

[Julien - ping for review, 2013/04/23 17:09:04]

Wouldn't it make more sense to have your vertices be LayoutUnits instead of
floats? Alternatively have FloatPolygon keep them as LayoutUnits?

As done, any subsequent operation(s) on your floats can yield to more instances
of this bug (not to mention that it is inefficient but that's not really a
problem for now).

[leviw_travelin_and_unemployed, 2013/04/23 18:27:20]

For the record, I agree that since this issue shows that we'll have problems
when Floats don't align to the LayoutUnit grid, it would make more sense to use
them for our vertices.

+{
+    for (unsigned i = 0; i < vertices.size(); ++i)
+        vertices[i].set(LayoutUnit(vertices[i].x()).toFloat(), LayoutUnit(vertices[i].y()).toFloat());

[Julien - ping for review, 2013/04/23 17:09:04]

Note that this could (and will) yield to big roundings as we have saturated
arithmetic enabled and the conversion to LayoutUnit involves a multiplication.

Also it may be nice to just use the existing FloatPoint -> LayoutPoint explicit
conversions (to choose whether you want to ceil / floor / something else)
instead of manually doing this conversion.

+}
+
 static inline FloatPolygon* computeShapePaddingBounds(const FloatPolygon& polygon, float padding, WindRule fillRule)
 {
     Vector<FloatPoint>* paddedVertices = new Vector<FloatPoint>();
@@ -146,6 +152,7 @@ static inline FloatPolygon* computeShapePaddingBounds(const FloatPolygon& polygo
             appendArc(*paddedVertices, thisEdge.vertex1(), padding, prevOffsetEdge.vertex2(), thisOffsetEdge.vertex1(), true);
     }
 
+    snapVerticesToLayoutUnitGrid(*paddedVertices);
     return new FloatPolygon(adoptPtr(paddedVertices), fillRule);
 }
 
@@ -166,6 +173,7 @@ static inline FloatPolygon* computeShapeMarginBounds(const FloatPolygon& polygon
             appendArc(*marginVertices, thisEdge.vertex1(), margin, prevOffsetEdge.vertex2(), thisOffsetEdge.vertex1(), false);
     }
 
+    snapVerticesToLayoutUnitGrid(*marginVertices);
     return new FloatPolygon(adoptPtr(marginVertices), fillRule);
 }