Harmonize FilterEffect::mapRect and mapPaintRect

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

Index: third_party/WebKit/Source/core/paint/SVGFilterPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/SVGFilterPainter.cpp b/third_party/WebKit/Source/core/paint/SVGFilterPainter.cpp
index 49c035b3a1e6abc0f5b03271856be7154a227cff..878c6bcb5712639ea5760d15a0137d0980cbc969 100644
--- a/third_party/WebKit/Source/core/paint/SVGFilterPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/SVGFilterPainter.cpp
@@ -48,7 +48,7 @@ void SVGFilterRecordingContext::endContent(FilterData* filterData)
     filterData->m_state = FilterData::ReadyToPaint;
 }
 
-static void paintFilteredContent(GraphicsContext& context, FilterData* filterData)
+static void paintFilteredContent(GraphicsContext& context, const LayoutObject& object, FilterData* filterData)
 {
     DCHECK_EQ(filterData->m_state, FilterData::ReadyToPaint);
     DCHECK(filterData->filter->getSourceGraphic());
@@ -60,7 +60,7 @@ static void paintFilteredContent(GraphicsContext& context, FilterData* filterDat
     context.save();
 
     // Clip drawing of filtered image to the minimum required paint rect.
-    context.clipRect(lastEffect->determineAbsolutePaintRect(lastEffect->absoluteBounds()));
+    context.clipRect(lastEffect->mapRect(object.strokeBoundingBox()));

[Stephen White, 2016/09/20 15:36:19]

Does mapRect() now take into effect filters which affect transparent black?
(This may become clear after I review more of this patch.)

[fs, 2016/09/20 19:14:14]

Yes, it should.

 
     FloatRect boundaries = filterData->filter->filterRegion();
     context.beginLayer(1, SkXfermode::kSrcOver_Mode, &boundaries, ColorFilterNone, std::move(imageFilter));

[Stephen White, 2016/09/20 15:36:19]

Not new to this patch, but Skia may ignore the boundaries passed to saveLayer()
with a filter which affects transparent black. So it looks like we may be
ignoring the filter region here. Perhaps we should be intersecting the bounds
computed by mapRect() above with the filter region, instead of passing it as
boundaries here, to ensure that it is properly clipped. I probably need to think
about this some more.

[fs, 2016/09/20 19:14:14]

mapRect() should apply that, which should hopefully be enough. Eventually we
won't be able to specify this here like this, so I guess we should ponder what
can be passed instead.

[Stephen White, 2016/09/20 19:46:38]

Eventually, we can probably pass nullptr, and just use the clip. Or even get rid
of saveLayer() altogether, and just use drawPaint() at the Skia level.

@@ -131,7 +131,7 @@ void SVGFilterPainter::finishEffect(const LayoutObject& object, SVGFilterRecordi
     FloatRect filterRegion = filterData ? filterData->filter->filterRegion() : FloatRect();
     LayoutObjectDrawingRecorder recorder(context, object, DisplayItem::kSVGFilter, filterRegion);
     if (filterData && filterData->m_state == FilterData::ReadyToPaint)
-        paintFilteredContent(context, filterData);
+        paintFilteredContent(context, object, filterData);
 }
 
 } // namespace blink