Include filter-generated content bounds in visual rects

third_party/WebKit/Source/core/paint/PaintLayer.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index f93d85f709d718c91fd9709c95732111197a0b20..c2d92f6dd3ee80333735cbba8640fb2c889c2395 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -1106,7 +1106,7 @@ LayoutRect PaintLayer::transparencyClipBox(const PaintLayer* layer, const PaintL
         // paints unfragmented.
         LayoutRect clipRect = layer->physicalBoundingBox(LayoutPoint());
         expandClipRectForDescendantsAndReflection(clipRect, layer, layer, transparencyBehavior, subPixelAccumulation, globalPaintFlags);
-        LayoutRect result = enclosingLayoutRect(transform.mapRect(layer->mapRectForFilter(FloatRect(clipRect))));
+        LayoutRect result = enclosingLayoutRect(transform.mapRect(layer->mapRectToAffectedFilterRegion(FloatRect(clipRect))));
         if (!paginationLayer)
             return result;
 
@@ -1124,7 +1124,7 @@ LayoutRect PaintLayer::transparencyClipBox(const PaintLayer* layer, const PaintL
 
     LayoutRect clipRect = layer->shouldFragmentCompositedBounds(rootLayer) ? layer->fragmentsBoundingBox(rootLayer) : layer->physicalBoundingBox(rootLayer);
     expandClipRectForDescendantsAndReflection(clipRect, layer, rootLayer, transparencyBehavior, subPixelAccumulation, globalPaintFlags);
-    clipRect = layer->mapLayoutRectForFilter(clipRect);
+    clipRect = layer->mapLayoutRectToAffectedFilterRegion(clipRect);
     clipRect.move(subPixelAccumulation);
     return clipRect;
 }
@@ -2250,7 +2250,7 @@ LayoutRect PaintLayer::boundingBoxForCompositing(const PaintLayer* ancestorLayer
         // Only enlarge by the filter outsets if we know the filter is going to be rendered in software.
         // Accelerated filters will handle their own outsets.
         if (paintsWithFilters())
-            result = mapLayoutRectForFilter(result);
+            result = mapLayoutRectToAffectedFilterRegion(result);
     }
 
     if (transform() && (options == IncludeTransformsAndCompositedChildLayers || ((paintsWithTransform(GlobalPaintNormalPhase) && (this != ancestorLayer || options == MaybeIncludeTransformForAncestorLayer)))))
@@ -2741,7 +2741,7 @@ FilterEffect* PaintLayer::lastFilterEffect() const
     return builder->lastEffect();
 }
 
-FloatRect PaintLayer::mapRectForFilter(const FloatRect& rect) const
+FloatRect PaintLayer::mapRectToAffectedFilterRegion(const FloatRect& rect) const
 {
     if (!hasFilterThatMovesPixels())
         return rect;
@@ -2749,14 +2749,23 @@ FloatRect PaintLayer::mapRectForFilter(const FloatRect& rect) const
     updateFilterEffectBuilder();
 
     FilterOperations filterOperations = computeFilterOperations(layoutObject()->styleRef());
-    return filterOperations.mapRect(rect);
+    FloatRect filteredRect = filterOperations.mapRect(rect);
+
+    // Some reference filters (e.g., FETurbulence, FETile) have effect bounds
+    // determined by the filter itself instead of the source rect.
+    if (filterOperations.hasReferenceFilter()) {
+        if (FilterEffect* lastEffect = lastFilterEffect())
+            filteredRect.unite(lastEffect->determineFilterPrimitiveSubregion(MapRectForward));

[Stephen White, 2016/08/25 15:03:14]

I think this is papering over the problem. I think the real problem is that we
need to expose a flavour of FilterOperations::mapRect() which calls
FilterEffect::mapPaintRect().

See the comment here, which explicitly calls out tile and displacement map:

https://cs.chromium.org/chromium/src/third_party/WebKit/Source/platform/graph...

OTOH, it would be nice if we could unite FilterEffect::mapRect() and
FilterEffect::mapPaintRect(). The latter was added by someone other than me, and
we should figure out what the differences really are for the paint case and why
they don't apply to the other cases. That's not clear to me.

Also, jbroman@ should probably take a look at this.

[pdr., 2016/08/29 17:51:12]

I've filed https://crbug.com/642035 as a brain-dump of my findings in this
patch. We do need to combine mapRect and mapPaintRect and use the result in
PaintLayer::mapRectForFilter, but this is a large project.

+    }
+
+    return filteredRect;
 }
 
-LayoutRect PaintLayer::mapLayoutRectForFilter(const LayoutRect& rect) const
+LayoutRect PaintLayer::mapLayoutRectToAffectedFilterRegion(const LayoutRect& rect) const
 {
     if (!hasFilterThatMovesPixels())
         return rect;
-    return enclosingLayoutRect(mapRectForFilter(FloatRect(rect)));
+    return enclosingLayoutRect(mapRectToAffectedFilterRegion(FloatRect(rect)));
 }
 
 bool PaintLayer::hasFilterThatMovesPixels() const