Support mask images for filter-based -webkit-box-reflect.

third_party/WebKit/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp

Index: third_party/WebKit/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp b/third_party/WebKit/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp
index 8c6bde04008815ca174b307c0ebd5dae467b0a4f..5ea2a36a6180bd6d32102a1c61e1b422347a074f 100644
--- a/third_party/WebKit/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp
+++ b/third_party/WebKit/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp
@@ -35,7 +35,9 @@
 #include "platform/graphics/filters/FilterOperations.h"
 #include "platform/graphics/filters/SourceGraphic.h"
 #include "platform/graphics/skia/SkiaUtils.h"
+#include "third_party/skia/include/core/SkPicture.h"
 #include "third_party/skia/include/core/SkXfermode.h"
+#include "third_party/skia/include/effects/SkPictureImageFilter.h"
 #include "third_party/skia/include/effects/SkXfermodeImageFilter.h"
 
 namespace blink {
@@ -185,9 +187,16 @@ sk_sp<SkImageFilter> SkiaImageFilterBuilder::buildTransform(const AffineTransfor
 
 sk_sp<SkImageFilter> SkiaImageFilterBuilder::buildBoxReflectFilter(const BoxReflection& reflection, sk_sp<SkImageFilter> input)
 {
-    sk_sp<SkImageFilter> maskedInput = input;
-    // TODO(jbroman): If a mask image is provided, mask!
-
+    sk_sp<SkImageFilter> maskedInput;
+    if (SkPicture* maskPicture = reflection.mask()) {
+        SkImageFilter::CropRect cropRect(maskPicture->cullRect());

[Stephen White, 2016/04/20 21:33:56]

Just wondering why a crop rect is necessary here. The SPIF's output should be
the picture's cullRect() in size, and SXIF should produce an output of the same
size. Is that not the case?

[jbroman, 2016/04/21 16:52:05]

My reading of SXIF is that it unites the source and destination rect when
choosing the default output size. The input image can, due to visual overflow,
be larger than the mask image, but since we definitely won't draw anything
outside the mask, it's unnecessary. SXIF could conceivably come to this
conclusion on its own by checking the particular xfer mode being used, but it
doesn't seem to do so.

[Stephen White, 2016/04/21 16:59:29]

Oh right, that makes sense. Would you log a skia bug to add that optimization,
and reference it here?

+        maskedInput = SkXfermodeImageFilter::Make(
+            SkXfermode::Make(SkXfermode::kSrcIn_Mode),
+            SkPictureImageFilter::Make(sk_ref_sp(maskPicture)),
+            input, &cropRect);
+    } else {
+        maskedInput = input;
+    }
     sk_sp<SkImageFilter> flipImageFilter = SkImageFilter::MakeMatrixFilter(
         reflection.reflectionMatrix(), kLow_SkFilterQuality, std::move(maskedInput));
     return SkXfermodeImageFilter::Make(nullptr, std::move(flipImageFilter), std::move(input), nullptr);