Make SkImageFilter crop rects relative to the primitive origin, instead of relative to their parent

src/effects/SkBitmapSource.cpp

 /*
  * Copyright 2012 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 "SkBitmapSource.h"
 #include "SkDevice.h"
 #include "SkCanvas.h"
@@ skipping 31 matching lines @@
 }
 
 bool SkBitmapSource::onFilterImage(Proxy* proxy, const SkBitmap&, const SkMatrix& matrix,
                                    SkBitmap* result, SkIPoint* offset) {
     SkRect bounds, dstRect;
     fBitmap.getBounds(&bounds);
     matrix.mapRect(&dstRect, fDstRect);
     if (fSrcRect == bounds && dstRect == bounds) {
         // No regions cropped out or resized; return entire bitmap.
         *result = fBitmap;
+        offset->fX = offset->fY = 0;
         return true;
     }
     SkIRect dstIRect;
     dstRect.roundOut(&dstIRect);
 
     SkAutoTUnref<SkBaseDevice> device(proxy->createDevice(dstIRect.width(), dstIRect.height()));
     if (NULL == device.get()) {
         return false;
     }
 
     SkCanvas canvas(device.get());
     SkPaint paint;
 
     // Subtract off the integer component of the translation (will be applied in loc, below).
     dstRect.offset(-SkIntToScalar(dstIRect.fLeft), -SkIntToScalar(dstIRect.fTop));
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
     // FIXME: this probably shouldn't be necessary, but drawBitmapRectToRect asserts
     // None filtering when it's translate-only
     paint.setFilterLevel(
         fSrcRect.width() == dstRect.width() && fSrcRect.height() == dstRect.height() ?
         SkPaint::kNone_FilterLevel : SkPaint::kMedium_FilterLevel);
     canvas.drawBitmapRectToRect(fBitmap, &fSrcRect, dstRect, &paint);
 
     *result = device.get()->accessBitmap(false);
-    offset->fX += dstIRect.fLeft;
-    offset->fY += dstIRect.fTop;
+    offset->fX = dstIRect.fLeft;
+    offset->fY = dstIRect.fTop;
     return true;
 }