Implement a computeFastBounds() traversal for SkImageFilter. This allows for correct culling of pri…

src/effects/SkOffsetImageFilter.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 "SkOffsetImageFilter.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
@@ skipping 47 matching lines @@
         canvas.translate(SkIntToScalar(srcOffset.fX - bounds.fLeft),
                          SkIntToScalar(srcOffset.fY - bounds.fTop));
         canvas.drawBitmap(src, fOffset.x(), fOffset.y(), &paint);
         *result = device->accessBitmap(false);
         offset->fX = bounds.fLeft;
         offset->fY = bounds.fTop;
     }
     return true;
 }
 
+void SkOffsetImageFilter::computeFastBounds(const SkRect& src, SkRect* dst) const {
+    if (getInput(0)) {
+        getInput(0)->computeFastBounds(src, dst);
+    } else {
+        *dst = src;
+    }
+    dst->offset(fOffset.fX, fOffset.fY);
+}
+
 bool SkOffsetImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
                                          SkIRect* dst) {
     SkVector vec;
     ctm.mapVectors(&vec, &fOffset, 1);
 
     *dst = src;
     dst->offset(SkScalarRoundToInt(vec.fX), SkScalarRoundToInt(vec.fY));
     return true;
 }
 
 void SkOffsetImageFilter::flatten(SkFlattenableWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);
     buffer.writePoint(fOffset);
 }
 
 SkOffsetImageFilter::SkOffsetImageFilter(SkScalar dx, SkScalar dy, SkImageFilter* input,
                                          const CropRect* cropRect) : INHERITED(input, cropRect) {
     fOffset.set(dx, dy);
 }
 
 SkOffsetImageFilter::SkOffsetImageFilter(SkFlattenableReadBuffer& buffer)
   : INHERITED(1, buffer) {
     buffer.readPoint(&fOffset);
     buffer.validate(SkScalarIsFinite(fOffset.fX) &&
                     SkScalarIsFinite(fOffset.fY));
 }