Implement correct clipping for image filters.

src/effects/SkDropShadowImageFilter.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDropShadowImageFilter.h"
 
 #include "SkBitmap.h"
@@ skipping 94 matching lines @@
     } else {
         *dst = src;
     }
 
     SkRect shadowBounds = *dst;
     shadowBounds.offset(fDx, fDy);
     shadowBounds.outset(SkScalarMul(fSigmaX, SkIntToScalar(3)),
                         SkScalarMul(fSigmaY, SkIntToScalar(3)));
     dst->join(shadowBounds);
 }
+
+bool SkDropShadowImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
+                                             SkIRect* dst) const {
+    SkIRect bounds = src;
+    if (getInput(0) && !getInput(0)->filterBounds(src, ctm, &bounds)) {
+        return false;
+    }
+    SkVector offsetVec, localOffsetVec = SkVector::Make(fDx, fDy);
+    ctm.mapVectors(&offsetVec, &localOffsetVec, 1);
+    bounds.offset(-SkScalarCeilToInt(offsetVec.x()),
+                  -SkScalarCeilToInt(offsetVec.y()));
+    SkVector sigma, localSigma = SkVector::Make(fSigmaX, fSigmaY);
+    ctm.mapVectors(&sigma, &localSigma, 1);
+    bounds.outset(SkScalarCeilToInt(SkScalarMul(sigma.x(), SkIntToScalar(3))),
+                  SkScalarCeilToInt(SkScalarMul(sigma.y(), SkIntToScalar(3))));
+    bounds.join(src);
+    *dst = bounds;
+    return true;
+}