Implement filter primitive subregion for reference CSS filters. This required refactoring determin…

Source/core/platform/graphics/filters/FilterEffect.cpp

Index: Source/core/platform/graphics/filters/FilterEffect.cpp
diff --git a/Source/core/platform/graphics/filters/FilterEffect.cpp b/Source/core/platform/graphics/filters/FilterEffect.cpp
index 920ae250b7d557dae9c5e4874e9afab671c777d9..0261babf68af4d308ea9d055e2cba84501b5aa6c 100644
--- a/Source/core/platform/graphics/filters/FilterEffect.cpp
+++ b/Source/core/platform/graphics/filters/FilterEffect.cpp
@@ -398,4 +398,46 @@ TextStream& FilterEffect::externalRepresentation(TextStream& ts, int) const
     return ts;
 }
 
+FloatRect FilterEffect::determineFilterPrimitiveSubregion()
+{
+    ASSERT(filter());
+
+    // FETile, FETurbulence, FEFlood don't have input effects, take the filter region as unite rect.
+    FloatRect subregion;
+    if (unsigned numberOfInputEffects = inputEffects().size()) {
+        subregion = inputEffect(0)->determineFilterPrimitiveSubregion();
+        for (unsigned i = 1; i < numberOfInputEffects; ++i)
+            subregion.unite(inputEffect(i)->determineFilterPrimitiveSubregion());
+    } else
+        subregion = filter()->filterRegionInUserSpace();
+
+    // After calling determineFilterPrimitiveSubregion on the target effect, reset the subregion again for <feTile>.
+    if (filterEffectType() == FilterEffectTypeTile)
+        subregion = filter()->filterRegionInUserSpace();
+
+    FloatRect boundaries = effectBoundaries();
+    if (hasX())
+        subregion.setX(boundaries.x());
+    if (hasY())
+        subregion.setY(boundaries.y());
+    if (hasWidth())
+        subregion.setWidth(boundaries.width());
+    if (hasHeight())
+        subregion.setHeight(boundaries.height());
+
+    setFilterPrimitiveSubregion(subregion);
+
+    FloatRect absoluteSubregion = filter()->absoluteTransform().mapRect(subregion);
+    FloatSize filterResolution = filter()->filterResolution();
+    absoluteSubregion.scale(filterResolution.width(), filterResolution.height());
+
+    // Clip every filter effect to the filter region.
+    FloatRect absoluteScaledFilterRegion = filter()->filterRegion();
+    absoluteScaledFilterRegion.scale(filterResolution.width(), filterResolution.height());
+    absoluteSubregion.intersect(absoluteScaledFilterRegion);
+
+    setMaxEffectRect(absoluteSubregion);
+    return subregion;
+}
+
 } // namespace WebCore