Fix MatrixImageFilter computeFastBounds

src/effects/SkMatrixImageFilter.cpp

 /*
  * Copyright 2014 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkMatrixImageFilter.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
@@ skipping 80 matching lines @@
     offset->fX = dstBounds.fLeft;
     offset->fY = dstBounds.fTop;
     return true;
 }
 
 void SkMatrixImageFilter::computeFastBounds(const SkRect& src, SkRect* dst) const {
     SkRect bounds = src;
     if (getInput(0)) {
         getInput(0)->computeFastBounds(src, &bounds);
     }
-    SkMatrix matrix;
-    matrix.setTranslate(-bounds.x(), -bounds.y());
-    matrix.postConcat(fTransform);
-    matrix.postTranslate(bounds.x(), bounds.y());
-    matrix.mapRect(dst, bounds);
+    fTransform.mapRect(dst, bounds);
+    dst->join(bounds);   // Work around for skia:3194

[Stephen White, 2014/12/08 17:20:51]

This really doesn't seem right to me, and we could come up with cases where
it'll fail. I think we really need the CTM here to do this correctly.

Granted, the original implementation wasn't correct either, but I'd rather get
us closer to correct than just paper over individual cases.

 }
 
 bool SkMatrixImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
                                          SkIRect* dst) const {
     SkMatrix transformInverse;
     if (!fTransform.invert(&transformInverse)) {
         return false;
     }
     SkMatrix matrix;
     if (!ctm.invert(&matrix)) {
         return false;
     }
     matrix.postConcat(transformInverse);
     matrix.postConcat(ctm);
     SkRect floatBounds;
     matrix.mapRect(&floatBounds, SkRect::Make(src));
     SkIRect bounds = floatBounds.roundOut();
     if (getInput(0) && !getInput(0)->filterBounds(bounds, ctm, &bounds)) {
         return false;
     }
 
     *dst = bounds;
     return true;
 }