clamp to premul in dither

Dither can bump color values above alpha (duh), or below
zero (duh), so clamp back to premul after dithering.

BUG=skia:6644,skia:6643

Change-Id: Ida107e866380e06130af0d01467117bca929ba44
Reviewed-on: https://skia-review.googlesource.com/17070
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/gm/bug6643.cpp b/gm/bug6643.cpp
new file mode 100644
index 0000000000..abe79fa756
--- /dev/null
+++ b/gm/bug6643.cpp
@@ -0,0 +1,29 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkGradientShader.h"
+#include "SkPictureRecorder.h"
+#include "gm.h"
+
+DEF_SIMPLE_GM(bug6643, canvas, 200, 200) {
+    SkColor colors[] = { SK_ColorTRANSPARENT, SK_ColorGREEN, SK_ColorTRANSPARENT };
+
+    SkPaint p;
+    p.setAntiAlias(true);
+    p.setShader(SkGradientShader::MakeSweep(100, 100, colors, nullptr, SK_ARRAY_COUNT(colors),
+                                            SkGradientShader::kInterpolateColorsInPremul_Flag,
+                                            nullptr));
+
+    SkPictureRecorder recorder;
+    recorder.beginRecording(200, 200)->drawPaint(p);
+
+    p.setShader(SkShader::MakePictureShader(recorder.finishRecordingAsPicture(),
+                                            SkShader::kRepeat_TileMode, SkShader::kRepeat_TileMode,
+                                            nullptr, nullptr));
+    canvas->drawColor(SK_ColorWHITE);
+    canvas->drawPaint(p);
+}