Add imagemasksubset GM

gm/imagemasksubset.cpp

Index: gm/imagemasksubset.cpp
diff --git a/gm/imagemasksubset.cpp b/gm/imagemasksubset.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..80e63f6bc7cad7714c4801a04534385e0e640744
--- /dev/null
+++ b/gm/imagemasksubset.cpp
@@ -0,0 +1,84 @@
+/*
+ * Copyright 2016 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 "SkCanvas.h"
+#include "SkImage.h"
+#include "SkImageGenerator.h"
+#include "SkSurface.h"
+#include "sk_tool_utils.h"
+
+namespace {
+
+const SkISize   kSize = SkISize::Make(100, 100);
+const SkIRect kSubset = SkIRect::MakeLTRB(25, 25, 75, 75);
+const SkRect    kDest = SkRect::MakeXYWH(10, 10, 100, 100);
+
+sk_sp<SkImage> make_mask(const sk_sp<SkSurface>& surface) {
+    sk_tool_utils::draw_checkerboard(surface->getCanvas(), 0x80808080, 0x00000000, 5);
+    return surface->makeImageSnapshot();
+}
+
+class MaskGenerator final : public SkImageGenerator {
+public:
+    MaskGenerator(const SkImageInfo& info) : INHERITED(info) {}
+
+    bool onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes, SkPMColor*,
+                     int*) override {
+        if (info.colorType() == kIndex_8_SkColorType) {
+            return false;
+        }
+
+        make_mask(SkSurface::MakeRasterDirect(info, pixels, rowBytes));
+        return true;
+    }
+
+private:
+    typedef SkImageGenerator INHERITED;
+};
+
+using MakerT = sk_sp<SkImage>(*)(SkCanvas*, const SkImageInfo&);
+const MakerT makers[] = {
+    // SkImage_Raster
+    [](SkCanvas*, const SkImageInfo& info) -> sk_sp<SkImage> {
+        return make_mask(SkSurface::MakeRaster(info));
+    },
+
+    // SkImage_Gpu
+    [](SkCanvas* c, const SkImageInfo& info) -> sk_sp<SkImage> {
+        sk_sp<SkSurface> surface;
+#if SK_SUPPORT_GPU
+        surface = SkSurface::MakeRenderTarget(c->getGrContext(), SkBudgeted::kNo, info);
+#endif
+        return make_mask(surface ? surface : SkSurface::MakeRaster(info));
+    },
+
+    // SkImage_Generator
+    [](SkCanvas*, const SkImageInfo& info) -> sk_sp<SkImage> {
+        return SkImage::MakeFromGenerator(new MaskGenerator(info));
+    },
+};
+
+} // anonymous ns
+
+// Checks whether subset SkImages preserve the original color type (A8 in this case).
+DEF_SIMPLE_GM(imagemasksubset, canvas, 480, 480) {
+    SkPaint paint;
+    paint.setColor(0xff00ff00);
+
+    const SkImageInfo info = SkImageInfo::MakeA8(kSize.width(), kSize.height());
+
+    for (size_t i = 0; i < SK_ARRAY_COUNT(makers); ++i) {
+        sk_sp<SkImage> image = makers[i](canvas, info);
+        if (image) {
+            canvas->drawImageRect(image, SkRect::Make(kSubset), kDest, &paint);
+            sk_sp<SkImage> subset = image->makeSubset(kSubset);
+            canvas->drawImageRect(subset, kDest.makeOffset(kSize.width() * 1.5f, 0), &paint);
+        }
+        canvas->translate(0, kSize.height() * 1.5f);
+    }
+}