Implement "hole" video frame.

cc/gl_renderer.cc

Index: cc/gl_renderer.cc
diff --git a/cc/gl_renderer.cc b/cc/gl_renderer.cc
index 42aaf8f6d9ea87a181eb4d04b174a69126aebfbf..cf9f4f39fdfc3fc84cf33dc4df0ed29bb12004a7 100644
--- a/cc/gl_renderer.cc
+++ b/cc/gl_renderer.cc
@@ -989,6 +989,16 @@ void GLRenderer::drawStreamVideoQuad(const DrawingFrame& frame, const StreamVide
     const VideoStreamTextureProgram* program = videoStreamTextureProgram();
     setUseProgram(program->program());
 
+    if (quad->texture_id == 0) {

[Vangelis Kokkevis, 2013/02/21 18:52:54]

I'm not too fond of the idea of using texture_id == 0 as a signal to punch a
hole, as it's also a possible valid failure condition. I'm thinking that we
should create a new quad type for holes that also uses a much simpler shader (no
need to do any sort of blending, just blast zeros to the backbuffer). 

[danakj, 2013/02/21 19:01:51]

That sounds like a solid color quad with needs blending forced off?

[wonsik2, 2013/02/26 04:52:24]

Created a new quad type; PTAL

[wonsik2, 2013/02/26 04:52:24]

I tried SolidColorDrawQuad with needs_blending == false, but it didn't work as
expected.

I ended up implementing a new quad. PTAL.

[wonsik2, 2013/02/26 06:47:03]

With further investigation, it turned out that an approach with
SolidColorDrawQuad worked.

+        // When texture_id == 0, punch a hole instead of rendering. The video
+        // will be composited outside of Chrome rendering pipeline, and where
+        // video should be composited should remain transparent in this case.
+        GLC(m_context, m_context->blendFunc(GL_ZERO, GL_ONE_MINUS_SRC_ALPHA));
+        drawQuadGeometry(frame, quad->quadTransform(), quad->rect, program->vertexShader().matrixLocation());
+        GLC(m_context, m_context->blendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA));
+        return;
+    }
+
     toGLMatrix(&glMatrix[0], quad->matrix);
     GLC(context(), context()->uniformMatrix4fv(program->vertexShader().texMatrixLocation(), 1, false, glMatrix));