add test for copy-on-write optimization

exercises a bug in the device-clip CL (hopefully to land soon)
BUG=skia:

Change-Id: I5a740280e1a3d6a4634338d04d9f1a1f9dc84dbb
Reviewed-on: https://skia-review.googlesource.com/9325
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/gm/surface.cpp b/gm/surface.cpp
index 6323c7047b..9c47b4badc 100644
--- a/gm/surface.cpp
+++ b/gm/surface.cpp
@@ -146,3 +146,26 @@ private:
     typedef GM INHERITED;
 };
 DEF_GM( return new NewSurfaceGM )
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+DEF_SIMPLE_GM(copy_on_write_retain, canvas, 256, 256) {
+    const SkImageInfo info = SkImageInfo::MakeN32Premul(256, 256);
+    sk_sp<SkSurface> surf = canvas->makeSurface(info, nullptr);
+    if (!surf) {
+        surf = SkSurface::MakeRaster(info, nullptr);
+    }
+
+    surf->getCanvas()->clear(SK_ColorRED);
+    // its important that image survives longer than the next draw, so the surface will see
+    // an outstanding image, and have to decide if it should retain or discard those pixels
+    sk_sp<SkImage> image = surf->makeImageSnapshot();
+
+    // normally a clear+opaque should trigger the discard optimization, but since we have a clip
+    // it should not (we need the previous red pixels).
+    surf->getCanvas()->clipRect(SkRect::MakeWH(128, 256));
+    surf->getCanvas()->clear(SK_ColorBLUE);
+
+    // expect to see two rects: blue | red
+    canvas->drawImage(surf->makeImageSnapshot(), 0, 0, nullptr);
+}