Add Alpha fade GM.
Review URL: https://codereview.chromium.org/804813009
diff --git a/gm/transparency.cpp b/gm/transparency.cpp
new file mode 100644
index 0000000..aeec31a
--- /dev/null
+++ b/gm/transparency.cpp
@@ -0,0 +1,74 @@
+/*
+ * Copyright 2015 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 "SkSurface.h"
+#include "gm.h"
+
+static void make_transparency(SkCanvas* canvas,
+ SkScalar width,
+ SkScalar height) {
+ SkPoint pts[2];
+ pts[0] = SkPoint::Make(0, 0);
+ pts[1] = SkPoint::Make(width, 0);
+ const SkColor kColors[] = {
+ SK_ColorBLACK,
+ SK_ColorGRAY,
+ SK_ColorWHITE,
+ SK_ColorRED,
+ SK_ColorYELLOW,
+ SK_ColorGREEN,
+ SK_ColorCYAN,
+ SK_ColorBLUE,
+ SK_ColorMAGENTA,
+ };
+ const SkScalar kRowHeight = height / SK_ARRAY_COUNT(kColors);
+ for (size_t i = 0; i < SK_ARRAY_COUNT(kColors); ++i) {
+ SkColor shaderColors[2];
+ shaderColors[0] = SK_AlphaTRANSPARENT;
+ shaderColors[1] = kColors[i];
+ SkAutoTUnref<SkShader> shader(SkGradientShader::CreateLinear(
+ pts, shaderColors, NULL, 2, SkShader::kClamp_TileMode));
+ SkRect r = SkRect::MakeXYWH(0, i * kRowHeight, width, kRowHeight);
+ SkPaint p;
+ p.setShader(shader);
+ canvas->drawRect(r, p);
+ }
+}
+
+// http://crrev.com/834303005
+static SkShader* create_checkerboard_shader(SkColor c1, SkColor c2, int size) {
+ SkBitmap bm;
+ bm.allocN32Pixels(2 * size, 2 * size);
+ bm.eraseColor(c1);
+ bm.eraseArea(SkIRect::MakeLTRB(0, 0, size, size), c2);
+ bm.eraseArea(SkIRect::MakeLTRB(size, size, 2 * size, 2 * size), c2);
+ return SkShader::CreateBitmapShader(bm, SkShader::kRepeat_TileMode,
+ SkShader::kRepeat_TileMode);
+}
+
+// http://crrev.com/834303005
+static void checkerboard(SkCanvas* canvas, SkColor c1, SkColor c2, int size) {
+ SkPaint paint;
+ paint.setShader(create_checkerboard_shader(c1, c2, size))->unref();
+ canvas->drawPaint(paint);
+}
+
+/**
+ * This GM verifies that a transparent bitmap drawn over a
+ * checkerboard pattern looks correct.
+ */
+DEF_SIMPLE_GM(transparency_check, canvas, 1912, 1080) {
+ checkerboard(canvas, 0xFF999999, 0xFF666666, 8);
+ {
+ SkAutoCanvasRestore autoCanvasRestore(canvas, true);
+ SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(256, 9));
+ make_transparency(surface->getCanvas(), 256.0f, 9.0f);
+ canvas->scale(7.5f, 120.0f);
+ surface->draw(canvas, 0, 0, NULL);
+ }
+}