Add Alpha Image GM

Change-Id: I835a59d9f8593e30db817dc8bd1d276af8c80cd7
Reviewed-on: https://skia-review.googlesource.com/24685
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>

gm/alpha_image.cpp

@@ -0,0 +1,54 @@
+/*
+ * 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 "gm.h"
+
+#include "SkBlurMaskFilter.h"
+#include "SkColorFilter.h"
+#include "SkImage.h"
+#include "SkShader.h"
+
+static SkBitmap make_alpha_image(int w, int h) {
+    SkBitmap bm;
+    bm.allocPixels(SkImageInfo::MakeA8(w, h));
+    bm.eraseARGB(10, 0, 0 , 0);
+    for (int y = 0; y < bm.height(); ++y) {
+        for (int x = y; x < bm.width(); ++x) {
+            *bm.getAddr8(x, y) = 0xFF;
+        }
+    }
+    bm.setImmutable();
+    return bm;
+}
+
+static sk_sp<SkColorFilter> make_color_filter() {
+    SkScalar colorMatrix[20] = {
+        1, 0, 0,   0,   0,
+        0, 1, 0,   0,   0,
+        0, 0, 0.5, 0.5, 0,
+        0, 0, 0.5, 0.5, 0}; // mix G and A.
+    return SkColorFilter::MakeMatrixFilterRowMajor255(colorMatrix);
+}
+
+DEF_SIMPLE_GM(alpha_image, canvas, 256, 256) {
+    auto image = SkImage::MakeFromBitmap(make_alpha_image(96, 96));
+    SkPaint paint;
+
+    paint.setColorFilter(make_color_filter());
+    paint.setMaskFilter(SkBlurMaskFilter::Make(kNormal_SkBlurStyle, 10.0f, 0));
+    canvas->drawImage(image.get(), 16, 16, &paint);
+
+    paint.setColorFilter(nullptr);
+    paint.setShader(SkShader::MakeColorShader(SK_ColorCYAN));
+    canvas->drawImage(image.get(), 144, 16, &paint);
+
+    paint.setColorFilter(make_color_filter());
+    canvas->drawImage(image.get(), 16, 144, &paint);
+
+    paint.setMaskFilter(nullptr);
+    canvas->drawImage(image.get(), 144, 144, &paint);
+}

gn/gm.gni

@@ -13,6 +13,7 @@ gm_sources = [
   "$_gm/aaxfermodes.cpp",
   "$_gm/addarc.cpp",
   "$_gm/all_bitmap_configs.cpp",
+  "$_gm/alpha_image.cpp",
   "$_gm/alphagradients.cpp",
   "$_gm/animatedGif.cpp",
   "$_gm/animatedimageblurs.cpp",