gpu, cmaa: add glApplyScreenSpaceAntialiasingCHROMIUM unittests

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 7b7def51edd37349492a3e9cbe089be975e76bcb..7132413f7366d7c3d3dd9a0a8328b56be4f7b7d1 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -16718,6 +16718,15 @@ void GLES2DecoderImpl::DoCreateAndConsumeTextureINTERNAL(
 }
 
 void GLES2DecoderImpl::DoApplyScreenSpaceAntialiasingCHROMIUM() {
+  Framebuffer* bound_framebuffer =
+      GetFramebufferInfoForTarget(GL_DRAW_FRAMEBUFFER);
+  if (!bound_framebuffer) {
+    LOCAL_SET_GL_ERROR(GL_INVALID_OPERATION,
+                       "glApplyScreenSpaceAntialiasingCHROMIUM",
+                       "no bound framebuffer object");
+    return;
+  }

[piman, 2016/10/20 18:36:17]

Can you update
gpu/GLES2/extensions/CHROMIUM/CHROMIUM_screen_space_antialiasing.txt to document
this new restriction?

What would be required to support it on the main framebuffer? In the future we
may want to do direct-to-main-framebuffer rendering for skia.

[dshwang, 2016/10/20 19:12:18]

good question.

https://cs.chromium.org/chromium/src/gpu/GLES2/extensions/CHROMIUM/CHROMIUM_s...

CHROMIUM_screen_space_antialiasing.txt already implies the extensions doesn't
work after glBindFramebuffer(0).

In fact, chromium implementation can work even after calling
glBindFramebuffer(0), because offscreen GLES2 decoder has FBO as default
framebuffer, rather than EGLSurface or something.

In summary, I add this restriction so that
CHROMIUM_screen_space_antialiasing.txt has simple explanation.

As far as I know, skia ganesh creates its own default FBO, rather than using
glBindFramebuffer(0), because it makes it efficient to do
canvas.draw(another_canvas).
When we support cmaa in skia and skia really need glBindFramebuffer(0), I will
change hear to support default FBO of offscreen GLES2 decoder, while it doesn't
support default FBO of onscreen GLES2 decoder tho.

+
   // Apply CMAA(Conservative Morphological Anti-Aliasing) algorithm to the
   // color attachments of currently bound draw framebuffer.
   // Reference GL_INTEL_framebuffer_CMAA for details.
@@ -16740,8 +16749,7 @@ void GLES2DecoderImpl::DoApplyScreenSpaceAntialiasingCHROMIUM() {
         return;
     }
     apply_framebuffer_attachment_cmaa_intel_
-        ->ApplyFramebufferAttachmentCMAAINTEL(
-            this, GetFramebufferInfoForTarget(GL_DRAW_FRAMEBUFFER));
+        ->ApplyFramebufferAttachmentCMAAINTEL(this, bound_framebuffer);
   }
 }