Make SkComposeImageFilter::onFilterImage filter the bounds given to the inner filter.

src/effects/SkComposeImageFilter.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 "SkComposeImageFilter.h"
 
 #include "SkReadBuffer.h"
 #include "SkSpecialImage.h"
 #include "SkWriteBuffer.h"
 
 
 void SkComposeImageFilter::computeFastBounds(const SkRect& src, SkRect* dst) const {
     SkImageFilter* outer = getInput(0);
     SkImageFilter* inner = getInput(1);
 
     SkRect tmp;
     inner->computeFastBounds(src, &tmp);
     outer->computeFastBounds(tmp, dst);
 }
 
 SkSpecialImage* SkComposeImageFilter::onFilterImage(SkSpecialImage* source, const Context& ctx,
                                                     SkIPoint* offset) const {
+    // The bounds passed to the inner filter must be filtered by the outer
+    // filter, so that the inner filter produces the pixels that the outer
+    // filter requires as input. This matters if the outer filter moves pixels.
+    SkIRect innerClipBounds;
+    getInput(0)->filterBounds(ctx.clipBounds(), ctx.ctm(), &innerClipBounds);
+    Context innerContext(ctx.ctm(), innerClipBounds, ctx.cache());
     SkIPoint innerOffset = SkIPoint::Make(0, 0);
-    SkAutoTUnref<SkSpecialImage> inner(this->filterInput(1, source, ctx, &innerOffset));
+    SkAutoTUnref<SkSpecialImage> inner(this->filterInput(1, source, innerContext, &innerOffset));
     if (!inner) {
         return nullptr;
     }
 
     SkMatrix outerMatrix(ctx.ctm());
     outerMatrix.postTranslate(SkIntToScalar(-innerOffset.x()), SkIntToScalar(-innerOffset.y()));
     SkIRect clipBounds = ctx.clipBounds();
     clipBounds.offset(-innerOffset.x(), -innerOffset.y());
     Context outerContext(outerMatrix, clipBounds, ctx.cache());
 
@@ skipping 33 matching lines @@
 
     str->appendf("outer: ");
     outer->toString(str);
 
     str->appendf("inner: ");
     inner->toString(str);
 
     str->appendf(")");
 }
 #endif