Fix bounds computations for SkDisplacementMapEffect with negative scale.

src/effects/SkDisplacementMapEffect.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 "SkDisplacementMapEffect.h"
 #include "SkDevice.h"
 #include "SkReadBuffer.h"
@@ skipping 251 matching lines @@
     offset->fY = bounds.top();
     return true;
 }
 
 void SkDisplacementMapEffect::computeFastBounds(const SkRect& src, SkRect* dst) const {
     if (this->getColorInput()) {
         this->getColorInput()->computeFastBounds(src, dst);
     } else {
         *dst = src;
     }
-    dst->outset(fScale * SK_ScalarHalf, fScale * SK_ScalarHalf);
+    dst->outset(SkScalarAbs(fScale) * SK_ScalarHalf, SkScalarAbs(fScale) * SK_ScalarHalf);
 }
 
 void SkDisplacementMapEffect::onFilterNodeBounds(const SkIRect& src, const SkMatrix& ctm,
                                    SkIRect* dst, MapDirection) const {
     *dst = src;
     SkVector scale = SkVector::Make(fScale, fScale);
     ctm.mapVectors(&scale, 1);
-    dst->outset(SkScalarCeilToInt(scale.fX * SK_ScalarHalf),
-                SkScalarCeilToInt(scale.fY * SK_ScalarHalf));
+    dst->outset(SkScalarCeilToInt(SkScalarAbs(scale.fX) * SK_ScalarHalf),
+                SkScalarCeilToInt(SkScalarAbs(scale.fY) * SK_ScalarHalf));
 }
 
 bool SkDisplacementMapEffect::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
                                    SkIRect* dst) const {
     SkIRect bounds;
     this->onFilterNodeBounds(src, ctm, &bounds, kReverse_MapDirection);
     if (this->getColorInput()) {
         return this->getColorInput()->filterBounds(bounds, ctm, dst);
     }
     *dst = bounds;
@@ skipping 349 matching lines @@
                                        const GrGLSLCaps&, GrProcessorKeyBuilder* b) {
     const GrDisplacementMapEffect& displacementMap = proc.cast<GrDisplacementMapEffect>();
 
     uint32_t xKey = displacementMap.xChannelSelector();
     uint32_t yKey = displacementMap.yChannelSelector() << kChannelSelectorKeyBits;
 
     b->add32(xKey | yKey);
 }
 #endif