[Slimming Paint] Implement deferred SVG filters

Source/core/rendering/svg/SVGRenderingContext.cpp

Index: Source/core/rendering/svg/SVGRenderingContext.cpp
diff --git a/Source/core/rendering/svg/SVGRenderingContext.cpp b/Source/core/rendering/svg/SVGRenderingContext.cpp
index fade7cdbfc7ac74d9b8230b186e54624e8465a31..80ba33330e7c9be53235cdb9f2df0632f15d71a6 100644
--- a/Source/core/rendering/svg/SVGRenderingContext.cpp
+++ b/Source/core/rendering/svg/SVGRenderingContext.cpp
@@ -34,6 +34,7 @@
 #include "core/rendering/svg/SVGResources.h"
 #include "core/rendering/svg/SVGResourcesCache.h"
 #include "platform/FloatConversion.h"
+#include "platform/graphics/paint/DrawingRecorder.h"
 
 namespace blink {
 
@@ -42,7 +43,13 @@ SVGRenderingContext::~SVGRenderingContext()
     if (m_filter) {
         ASSERT(SVGResourcesCache::cachedResourcesForRenderObject(m_object));
         ASSERT(SVGResourcesCache::cachedResourcesForRenderObject(m_object)->filter() == m_filter);
-        m_filter->finishEffect(m_object, m_paintInfo.context);
+
+        DrawingRecorder recorder(m_originalPaintInfo->context, m_object->displayItemClient(), DisplayItem::SVGFilter, LayoutRect::infiniteRect());
+        m_filter->finishEffect(m_object, m_originalPaintInfo->context);
+
+        // Reset the paint info after the filter effect has been completed.
+        m_paintInfo.context = m_originalPaintInfo->context;
+        m_paintInfo.rect = m_originalPaintInfo->rect;

[fs, 2015/01/26 09:47:11]

m_paintInfo.rect is "dead" at this point (not used below this point, and scopes
out at the end of this function.) Might be worth adding a note/assert/something
to that effect?

(With this line of reasoning I suppose m_originalPaintInfo->context could be
passed to the other two finishEffect()s as well... since m_paintInfo.context ===
m_originalPaintInfo->context after this point. A think a note will do fine
though at this point.)

[pdr., 2015/01/28 01:04:39]

Yeah, I thought it would be clean to fully clean up even though it isn't used
today (or, likely ever). I'll add a note.

     }
 
     if (m_masker) {
@@ -149,10 +156,15 @@ bool SVGRenderingContext::applyFilterIfNecessary(SVGResources* resources)
         if (m_object->style()->svgStyle().hasFilter())
             return false;
     } else if (RenderSVGResourceFilter* filter = resources->filter()) {
-        if (!filter->prepareEffect(m_object, m_paintInfo.context))
+        GraphicsContext* filterContext = filter->prepareEffect(m_object, m_paintInfo.context);
+        if (!filterContext)
             return false;
         m_filter = filter;
 
+        // Because the filter needs to cache its contents we replace the context
+        // during filtering with the filter's context.
+        m_paintInfo.context = filterContext;
+
         // Because we cache the filter contents and do not invalidate on paint
         // invalidation rect changes, we need to paint the entire filter region
         // so elements outside the initial paint (due to scrolling, etc) paint.