Image filters: fix filtering of transparent black in CFIF.

SkColorFilterImageFilter has a codepath to filter transparent black
regions outside of the input image. However, it was treating the
exterior as opaque black, rather than trasparent black.

Note: the results of imagefiltercropexpand GM will change, as it
was tweaked a bit to show this bug.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1978363002
NOTREECHECKS=true
NOTRY=true
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/1978363002

1 files changed, 5 insertions, 3 deletions

diff --git a/gm/imagefilterscropexpand.cpp b/gm/imagefilterscropexpand.cpp
index 4ce845d9ee..9b9f7ee817 100644
--- a/gm/imagefilterscropexpand.cpp
+++ b/gm/imagefilterscropexpand.cpp
@@ -50,11 +50,13 @@ protected:
 
         sk_sp<SkImageFilter> gradientCircleSource(SkImageSource::Make(std::move(gradientCircle)));
         sk_sp<SkImageFilter> noopCropped(SkOffsetImageFilter::Make(0, 0, nullptr, &cropRect));
-        SkScalar sk255 = SkIntToScalar(255);
+        // This color matrix saturates the green component but only partly increases the opacity.
+        // For the opaque checkerboard, the opacity boost doesn't matter but it does impact the
+        // area outside the checkerboard.
         SkScalar matrix[20] = { 1, 0, 0, 0, 0,
-                                0, 1, 0, 0, sk255,
+                                0, 1, 0, 0, 255,
                                 0, 0, 1, 0, 0,
-                                0, 0, 0, 0, sk255 };
+                                0, 0, 0, 1, 32 };
         sk_sp<SkColorFilter> cfAlphaTrans(SkColorFilter::MakeMatrixFilterRowMajor255(matrix));
 
         SkRect r = SkRect::MakeWH(SkIntToScalar(64), SkIntToScalar(64));