Fix SkComposeImageFilter's bounds computation and offset handling

src/effects/SkComposeImageFilter.cpp

Index: src/effects/SkComposeImageFilter.cpp
diff --git a/src/effects/SkComposeImageFilter.cpp b/src/effects/SkComposeImageFilter.cpp
index 4a17e152de704d7b0369ea9ba3f2c731632ea0ec..2b1606a8a40b0a12570af65416754eb698a0cb5c 100644
--- a/src/effects/SkComposeImageFilter.cpp
+++ b/src/effects/SkComposeImageFilter.cpp
@@ -13,6 +13,15 @@
 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,
@@ -22,8 +31,20 @@ bool SkComposeImageFilter::onFilterImage(Proxy* proxy,
     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,