Harmonize FilterEffect::mapRect and mapPaintRect

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/SVGFilterPainter.h"
 
 #include "core/layout/svg/LayoutSVGResourceFilter.h"
 #include "core/paint/FilterEffectBuilder.h"
 #include "core/paint/LayoutObjectDrawingRecorder.h"
 #include "platform/graphics/filters/SkiaImageFilterBuilder.h"
@@ skipping 30 matching lines @@
 
     SkiaImageFilterBuilder::buildSourceGraphic(sourceGraphic, m_context->endRecording());
 
     // Content is cached by the source graphic so temporaries can be freed.
     m_paintController = nullptr;
     m_context = nullptr;
 
     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());
 
     filterData->m_state = FilterData::PaintingFilter;
 
     FilterEffect* lastEffect = filterData->filter->lastEffect();
     sk_sp<SkImageFilter> imageFilter = SkiaImageFilterBuilder::build(lastEffect, ColorSpaceDeviceRGB);
     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.

     context.endLayer();
     context.restore();
 
     filterData->m_state = FilterData::ReadyToPaint;
 }
 
 GraphicsContext* SVGFilterPainter::prepareEffect(const LayoutObject& object, SVGFilterRecordingContext& recordingContext)
 {
     m_filter.clearInvalidationMask();
 
@@ skipping 47 matching lines @@
             filterData->m_state = FilterData::RecordingContent;
     }
 
     GraphicsContext& context = recordingContext.paintingContext();
     if (LayoutObjectDrawingRecorder::useCachedDrawingIfPossible(context, object, DisplayItem::kSVGFilter))
         return;
 
     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