Use Offscreen Surface for Split Screen

tools/viewer/sk_app/Window.h

Index: tools/viewer/sk_app/Window.h
diff --git a/tools/viewer/sk_app/Window.h b/tools/viewer/sk_app/Window.h
index 8b1378a80fdb6669e24102d8cbce7af2ef1f7f81..8ce874cde49282d05dba2a39ea51162e11388728 100644
--- a/tools/viewer/sk_app/Window.h
+++ b/tools/viewer/sk_app/Window.h
@@ -15,6 +15,7 @@
 #include "SkJSONCPP.h"
 
 class SkCanvas;
+class SkSurface;
 
 namespace sk_app {
 
@@ -161,6 +162,8 @@ public:
     virtual const DisplayParams& getDisplayParams();
     void setDisplayParams(const DisplayParams& params);
 
+    sk_sp<SkSurface> getOffscreenSurface(bool sRGB);

[djsollen, 2016/06/15 14:14:29]

why not pass SkSurfaceProps as an argument so that it is consistent with our
other APIs?

[liyuqian, 2016/06/15 16:43:12]

Because SkSurfaceProps is kind of complicated to construct. A lot of that work
is done in WindowContext::createRenderSurface. This simplified API reuses that
code. I'll add comment to this method to specify that this API is only for split
screen usage. Hopefully that will make things clear?

+
 protected:
     Window();