Fix SkComposeImageFilter's bounds computation and offset handling

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 "SkBitmap.h"
 #include "SkComposeImageFilter.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 
 SkComposeImageFilter::~SkComposeImageFilter() {
 }
 
+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);
+}
+
 bool SkComposeImageFilter::onFilterImage(Proxy* proxy,
                                          const SkBitmap& src,
                                          const Context& ctx,
                                          SkBitmap* result,
                                          SkIPoint* offset) const {
     SkImageFilter* outer = getInput(0);
     SkImageFilter* inner = getInput(1);
 
     SkBitmap tmp;
-    return inner->filterImage(proxy, src, ctx, &tmp, offset) &&
-           outer->filterImage(proxy, tmp, ctx, result, offset);
+    SkIPoint innerOffset = SkIPoint::Make(0, 0);
+    SkIPoint outerOffset = SkIPoint::Make(0, 0);
+    if (!inner->filterImage(proxy, src, ctx, &tmp, &innerOffset))
+        return false;
+
+    SkMatrix outerMatrix(ctx.ctm());
+    outerMatrix.postTranslate(SkIntToScalar(-innerOffset.x()), SkIntToScalar(-innerOffset.y()));
+    Context outerContext(outerMatrix, ctx.clipBounds(), ctx.cache());
+    if (!outer->filterImage(proxy, tmp, outerContext, result, &outerOffset)) {
+        return false;
+    }
+
+    *offset = innerOffset + outerOffset;
+    return true;
 }
 
 bool SkComposeImageFilter::onFilterBounds(const SkIRect& src,
                                           const SkMatrix& ctm,
                                           SkIRect* dst) const {
     SkImageFilter* outer = getInput(0);
     SkImageFilter* inner = getInput(1);
 
     SkIRect tmp;
     return inner->filterBounds(src, ctm, &tmp) && outer->filterBounds(tmp, ctm, dst);
@@ skipping 13 matching lines @@
 
     str->appendf("outer: ");
     outer->toString(str);
 
     str->appendf("inner: ");
     inner->toString(str);
 
     str->appendf(")");
 }
 #endif