Fix SkComposeImageFilter's bounds computation and offset handling

tests/ImageFilterTest.cpp

Index: tests/ImageFilterTest.cpp
diff --git a/tests/ImageFilterTest.cpp b/tests/ImageFilterTest.cpp
index 55499d74c37058e79b035ec230743c6996c61899..fd7cfed486ea834d320badd31d7888b39a1eaca6 100644
--- a/tests/ImageFilterTest.cpp
+++ b/tests/ImageFilterTest.cpp
@@ -12,6 +12,7 @@
 #include "SkCanvas.h"
 #include "SkColorFilterImageFilter.h"
 #include "SkColorMatrixFilter.h"
+#include "SkComposeImageFilter.h"
 #include "SkDeviceImageFilterProxy.h"
 #include "SkDisplacementMapEffect.h"
 #include "SkDropShadowImageFilter.h"
@@ -584,6 +585,20 @@ DEF_TEST(ImageFilterDilateThenBlurBounds, reporter) {
     REPORTER_ASSERT(reporter, bounds == expectedBounds);
 }
 
+DEF_TEST(ImageFilterComposedBlurFastBounds, reporter) {
+    SkAutoTUnref<SkImageFilter> filter1(makeBlur());
+    SkAutoTUnref<SkImageFilter> filter2(makeBlur());
+    SkAutoTUnref<SkImageFilter> composedFilter(SkComposeImageFilter::Create(filter1.get(), filter2.get()));
+
+    SkRect boundsSrc = SkRect::MakeWH(SkIntToScalar(100), SkIntToScalar(100));
+    SkRect expectedBounds = SkRect::MakeXYWH(
+        SkIntToScalar(-6), SkIntToScalar(-6), SkIntToScalar(112), SkIntToScalar(112));
+    SkRect boundsDst = SkRect::MakeEmpty();
+    composedFilter->computeFastBounds(boundsSrc, &boundsDst);
+
+    REPORTER_ASSERT(reporter, boundsDst == expectedBounds);
+}
+
 static void draw_blurred_rect(SkCanvas* canvas) {
     SkAutoTUnref<SkImageFilter> filter(SkBlurImageFilter::Create(SkIntToScalar(8), 0));
     SkPaint filterPaint;
@@ -1068,6 +1083,23 @@ DEF_TEST(XfermodeImageFilterCroppedInput, reporter) {
     test_xfermode_cropped_input(&device, reporter);
 }
 
+DEF_TEST(ComposedImageFilterOffset, reporter) {
+    SkBitmap bitmap;
+    bitmap.allocN32Pixels(100, 100);
+    bitmap.eraseARGB(0, 0, 0, 0);
+    SkBitmapDevice device(bitmap);
+    SkDeviceImageFilterProxy proxy(&device, SkSurfaceProps(SkSurfaceProps::kLegacyFontHost_InitType));
+
+    SkImageFilter::CropRect cropRect(SkRect::MakeXYWH(1, 0, 20, 20));
+    SkAutoTUnref<SkImageFilter> offsetFilter(SkOffsetImageFilter::Create(0, 0, NULL, &cropRect));
+    SkAutoTUnref<SkImageFilter> composedFilter(SkComposeImageFilter::Create(makeBlur(), offsetFilter.get()));
+    SkBitmap result;
+    SkIPoint offset;
+    SkImageFilter::Context ctx(SkMatrix::I(), SkIRect::MakeLargest(), NULL);
+    REPORTER_ASSERT(reporter, composedFilter->filterImage(&proxy, bitmap, ctx, &result, &offset));
+    REPORTER_ASSERT(reporter, offset.fX == 1 && offset.fY == 0);
+}
+
 #if SK_SUPPORT_GPU
 const SkSurfaceProps gProps = SkSurfaceProps(SkSurfaceProps::kLegacyFontHost_InitType);