commit bb654fc24858b7b6a70dce187f9b8940de5b0674
author Stan Iliev <stililiev@gmail.com> Wed Jan 18 20:09:31 2023 -0800
committer SkCQ <skcq-be@skia-corp.google.com.iam.gserviceaccount.com> Tue Jan 24 16:07:57 2023 +0000
tree 50caa3f9f6146b3d10d611df0edcfaf8fa9c1b30
parent 1bc48bcb1201ea4b3c89d56339e6c996e37a5730

Fix correctness issue with SkImageImageFilter and unpremul images

Unpremul images passed to SkImageImageFilter draw incorrectly, when an intermediate SurfaceContext is not used.
For repro steps see https://fiddle.skia.org/c/76d202e60b05a6aab9c8a074863f0b68.
CL fixes SkSpecialImage::MakeFromImage to not hardcode premul alpha type, but read alpha type from the source SkImage.
CL fixes SkImageImageFilter to generate correct fragment shader for unpremul images: e.g. color.rgb *= color.a.

Bug: skia:14045
Change-Id: I3b27849d64294efc783bebcc62d66ff59e164a15
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/630196
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>

gm/imagefiltersunpremul.cpp

diff --git a/gm/imagefiltersunpremul.cpp b/gm/imagefiltersunpremul.cpp
new file mode 100644
index 0000000..82b4288
--- /dev/null
+++ b/gm/imagefiltersunpremul.cpp
@@ -0,0 +1,25 @@
+/*
+ * Copyright 2023 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm/gm.h"
+#include "include/core/SkBitmap.h"
+#include "include/core/SkCanvas.h"
+#include "include/core/SkColor.h"
+#include "include/core/SkImage.h"
+#include "include/core/SkPaint.h"
+#include "include/effects/SkImageFilters.h"
+
+DEF_SIMPLE_GM_BG(imagefiltersunpremul, canvas, 64, 64, SK_ColorBLACK) {
+    // Draw an kUnpremul_SkAlphaType image using SkImageFilters::Image() and
+    // verify alpha channel was blended correctly.
+    SkBitmap bitmap;
+    bitmap.allocPixels(SkImageInfo::Make(64, 64, kRGBA_8888_SkColorType, kUnpremul_SkAlphaType));
+    bitmap.eraseColor(SkColorSetARGB(50, 255, 0, 0));
+    SkPaint paint;
+    paint.setImageFilter(SkImageFilters::Image(SkImage::MakeFromBitmap(bitmap)));
+    canvas->drawPaint(paint);
+}

gn/gm.gni

diff --git a/gn/gm.gni b/gn/gm.gni
index bdf4192..b951c22 100644
--- a/gn/gm.gni
+++ b/gn/gm.gni
@@ -228,6 +228,7 @@
   "$_gm/imagefiltersscaled.cpp",
   "$_gm/imagefiltersstroked.cpp",
   "$_gm/imagefilterstransformed.cpp",
+  "$_gm/imagefiltersunpremul.cpp",
   "$_gm/imagefromyuvtextures.cpp",
   "$_gm/imagemagnifier.cpp",
   "$_gm/imagemakewithfilter.cpp",

src/core/SkSpecialImage.cpp

diff --git a/src/core/SkSpecialImage.cpp b/src/core/SkSpecialImage.cpp
index 1a16c94..580c0bc 100644
--- a/src/core/SkSpecialImage.cpp
+++ b/src/core/SkSpecialImage.cpp
@@ -134,7 +134,7 @@
                                    subset,
                                    image->uniqueID(),
                                    std::move(view),
-                                   { ct, kPremul_SkAlphaType, image->refColorSpace() },
+                                   { ct, image->alphaType(), image->refColorSpace() },
                                    props);
     }
 #endif