Ensure filter and reflection outsets are applied on paint invalidation rect

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 70e2509cb39ec661154035ac38b7e44ec691b6e9..a2256666220b04b9be9da6734fa2eeff32a36d6b 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -1971,10 +1971,7 @@ LayoutRect LayoutBox::localOverflowRectForPaintInvalidation() const
 
 bool LayoutBox::mapToVisualRectInAncestorSpace(const LayoutBoxModelObject* ancestor, LayoutRect& rect, VisualRectFlags visualRectFlags) const
 {
-    // We need to inflate the paint invalidation rect before we use paintInvalidationState,
-    // else we would forget to inflate it for the current layoutObject. FIXME: If these were
-    // included into the visual overflow for paint invalidation, we wouldn't have this issue.
-    inflatePaintInvalidationRectForReflectionAndFilter(rect);
+    inflateVisualRectForReflectionAndFilter(rect);
 
     if (ancestor == this) {
         // The final rect returned is always in the physical coordinate space of the ancestor.
@@ -1983,10 +1980,32 @@ bool LayoutBox::mapToVisualRectInAncestorSpace(const LayoutBoxModelObject* ances
     }
 
     bool ancestorSkipped;
-    LayoutObject* container = this->container(ancestor, &ancestorSkipped);
+    bool filterOrReflectionSkipped;
+    LayoutObject* container = this->container(ancestor, &ancestorSkipped, &filterOrReflectionSkipped);
     if (!container)
         return true;
 
+    if (filterOrReflectionSkipped) {

[chrishtr, 2016/05/03 17:31:38]

Please factor the contents of this if into a helper method.

[Xianzhu, 2016/05/03 18:00:24]

Done.

+        // Apply filter and reflection outsets between this object and container or ancestor.

[jbroman, 2016/05/03 17:30:48]

Suggest not phrasing this as "outsets". Not all filters are blur-like.

For instance, an offset filter shifts the image (while that _can_ be viewed as
an outset, it's pretty awkward to as it isn't an expansion). And with
reflections it's even more different (in particular, it's sensitive to the
coordinate space being used).

Characterizing this the way Blink is trending toward -- and the way Skia does --
is better: there's a function mapping rectangles through filters (forwards or
backwards, depending on the case).

[Xianzhu, 2016/05/03 18:00:24]

Thanks for the info. Done.

+        LayoutSize offsetFromContainer = this->offsetFromContainer(container);
+        rect.move(offsetFromContainer);
+        for (LayoutObject* parent = this->parent(); parent && parent != container; parent = parent->parent()) {
+            if (parent->isBox()) {
+                // If the ancestor is below o, then we need to map the rect into ancestor's coordinates.
+                LayoutSize parentOffset = parent->offsetFromAncestorContainer(container);

[chrishtr, 2016/05/03 17:31:38]

This is expensive, but I suppose this whole situation is quite rare, so ok?

[Xianzhu, 2016/05/03 18:00:24]

I believe it's rare because no layout test covered this, and no bug report for
it.

+                rect.move(-parentOffset);
+                toLayoutBox(parent)->inflateVisualRectForReflectionAndFilter(rect);
+                rect.move(parentOffset);
+            }
+            if (parent == ancestor) {
+                // We meet ancestor before container.
+                ASSERT(ancestorSkipped);
+                break;
+            }
+        }
+        rect.move(-offsetFromContainer);
+    }
+
     // The rect we compute at each step is shifted by our x/y offset in the parent container's coordinate space.
     // Only when we cross a writing mode boundary will we have to possibly flipForWritingMode (to convert into a more
     // appropriate offset corner for the enclosing container).
@@ -2043,7 +2062,7 @@ bool LayoutBox::mapToVisualRectInAncestorSpace(const LayoutBoxModelObject* ances
         return container->mapToVisualRectInAncestorSpace(ancestor, rect, visualRectFlags);
 }
 
-void LayoutBox::inflatePaintInvalidationRectForReflectionAndFilter(LayoutRect& paintInvalidationRect) const
+void LayoutBox::inflateVisualRectForReflectionAndFilter(LayoutRect& paintInvalidationRect) const
 {
     if (!RuntimeEnabledFeatures::cssBoxReflectFilterEnabled() && hasReflection())
         paintInvalidationRect.unite(reflectedRect(paintInvalidationRect));