Implement correct clipping for image filters.

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 08b09e8e2b6e970b06d93c0449b9af8859573173..c2e36b319157c85ac5cb25e3b15d9f8113d51017 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -791,11 +791,18 @@ static bool bounds_affects_clip(SkCanvas::SaveFlags flags) {
 }
 
 bool SkCanvas::clipRectBounds(const SkRect* bounds, SaveFlags flags,
-                               SkIRect* intersection) {
+                               SkIRect* intersection, const SkImageFilter* imageFilter) {
     SkIRect clipBounds;
+    SkRegion::Op op = SkRegion::kIntersect_Op;
     if (!this->getClipDeviceBounds(&clipBounds)) {
         return false;
     }
+
+    if (imageFilter) {
+        imageFilter->filterBounds(clipBounds, *fMCRec->fMatrix, &clipBounds);
+        // Filters may grow the bounds beyond the device bounds.
+        op = SkRegion::kReplace_Op;

[reed1, 2014/02/04 15:30:08]

Hmm, this make me nervous. I understand that the offscreen needs to be larger
sometimes for the imagefilter to avoid edge-artifacts. It seems odd that we are
expanding "the" clip, when all we really want to do is expand the offscreen's
bounds (and keep its clip open), since on restore() the original clip is fine
(need not be expanded).

[Stephen White, 2014/02/04 16:01:41]

I'm pretty sure we also need to expand the clip inside the saveLayer(), since 
otherwise the primitives that are drawn there will be clipped against the 
original device bounds. However, it shouldn't affect the main clip, since the 
saveLayer() for image filters always saves the clip and restores it before the 
drawDevice() which applies the filters.

However, if there's a better way of accomplishing this, I'm open to suggestions.

+    }
     SkIRect ir;
     if (NULL != bounds) {
         SkRect r;
@@ -813,11 +820,11 @@ bool SkCanvas::clipRectBounds(const SkRect* bounds, SaveFlags flags,
         ir = clipBounds;
     }
 
-    fClipStack.clipDevRect(ir, SkRegion::kIntersect_Op);
+    fClipStack.clipDevRect(ir, op);
 
     // early exit if the clip is now empty
     if (bounds_affects_clip(flags) &&
-        !fMCRec->fRasterClip->op(ir, SkRegion::kIntersect_Op)) {
+        !fMCRec->fRasterClip->op(ir, op)) {
         return false;
     }
 
@@ -841,7 +848,7 @@ int SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint,
     fDeviceCMDirty = true;
 
     SkIRect ir;
-    if (!this->clipRectBounds(bounds, flags, &ir)) {
+    if (!this->clipRectBounds(bounds, flags, &ir, paint ? paint->getImageFilter() : NULL)) {
         return count;
     }