Fix bounds computations for SkDisplacementMapEffect with negative scale.

gm/displacement.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 "SkImage.h"
 #include "SkImageSource.h"
@@ skipping 25 matching lines @@
             sk_tool_utils::create_checkerboard_bitmap(64, 64, c1, c2, 8)));
         fLarge.reset(SkImage::NewFromBitmap(
             sk_tool_utils::create_checkerboard_bitmap(96, 96, c1, c2, 8)));
         fLargeW.reset(
             SkImage::NewFromBitmap(sk_tool_utils::create_checkerboard_bitmap(96, 64, c1, c2, 8)));
         fLargeH.reset(SkImage::NewFromBitmap(
             sk_tool_utils::create_checkerboard_bitmap(64, 96, c1, c2, 8)));
     }
 
     SkISize onISize() override {
-        return SkISize::Make(500, 500);
+        return SkISize::Make(600, 500);
     }
 
     void drawClippedBitmap(SkCanvas* canvas, int x, int y, const SkPaint& paint) const {
         canvas->save();
         canvas->translate(SkIntToScalar(x), SkIntToScalar(y));
         canvas->clipRect(SkRect::MakeWH(SkIntToScalar(fBitmap.width()), SkIntToScalar(fBitmap.height())));
         canvas->drawBitmap(fBitmap, 0, 0, &paint);
         canvas->restore();
     }
 
@@ skipping 89 matching lines @@
             SkDisplacementMapEffect::kG_ChannelSelectorType,
             SkDisplacementMapEffect::kA_ChannelSelectorType,
             40.0f, displ, nullptr, &cropRect))->unref();
         drawClippedBitmap(canvas, 300, 300, paint);
         paint.setImageFilter(SkDisplacementMapEffect::Create(
             SkDisplacementMapEffect::kR_ChannelSelectorType,
             SkDisplacementMapEffect::kA_ChannelSelectorType,
             40.0f, displ, nullptr, &cropRect))->unref();
         drawClippedBitmap(canvas, 400, 300, paint);
 
+        // Test for negative scale.
+        paint.setImageFilter(SkDisplacementMapEffect::Create(
+            SkDisplacementMapEffect::kG_ChannelSelectorType,
+            SkDisplacementMapEffect::kA_ChannelSelectorType,
+            -40.0f, displ))->unref();
+        this->drawClippedBitmap(canvas, 500, 0, paint);
+
         // Tests for images of different sizes
         displ.reset(SkImageSource::Create(fSmall));
         paint.setImageFilter(SkDisplacementMapEffect::Create(
             SkDisplacementMapEffect::kR_ChannelSelectorType,
             SkDisplacementMapEffect::kG_ChannelSelectorType,
             40.0f, displ))->unref();
         drawClippedBitmap(canvas, 0, 400, paint);
         displ.reset(SkImageSource::Create(fLarge));
         paint.setImageFilter(SkDisplacementMapEffect::Create(
             SkDisplacementMapEffect::kB_ChannelSelectorType,
@@ skipping 27 matching lines @@
     SkBitmap fBitmap;
     SkAutoTUnref<SkImage> fCheckerboard, fSmall, fLarge, fLargeW, fLargeH;
 
     typedef GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 DEF_GM(return new DisplacementMapGM;)
 }