Implement EXT_draw_buffers WebGL extention support in command buffer.

gpu/command_buffer/service/framebuffer_manager.cc

Index: gpu/command_buffer/service/framebuffer_manager.cc
===================================================================
--- gpu/command_buffer/service/framebuffer_manager.cc	(revision 186778)
+++ gpu/command_buffer/service/framebuffer_manager.cc	(working copy)
@@ -254,6 +254,9 @@
       has_been_bound_(false),
       framebuffer_complete_state_count_id_(0) {
   manager->StartTracking(this);
+  draw_buffers_[0] = GL_COLOR_ATTACHMENT0;
+  for (GLsizei i = 1; i < kMaxDrawBuffers; ++i)
+    draw_buffers_[i] = GL_NONE;
 }
 
 Framebuffer::~Framebuffer() {
@@ -402,6 +405,19 @@
   return true;
 }
 
+GLenum Framebuffer::GetDrawBuffer(GLenum draw_buffer) const {
+  GLsizei index = static_cast<GLsizei>(
+      draw_buffer - GL_DRAW_BUFFER0_ARB);
+  CHECK(index >= 0 && index < kMaxDrawBuffers);

[greggman, 2013/03/08 21:48:28]

Do these need to be CHECKs? We don't do CHECKS for this kind of anywhere else.
CHECKs leave code in on release. It should be impossible to call this with a bad
value. DCHECK?

[Zhenyao Mo, 2013/03/13 01:22:02]

Done.

+  return draw_buffers_[index];
+}
+
+void Framebuffer::SetDrawBuffers(GLsizei n, const GLenum* bufs) {
+  CHECK(n <= kMaxDrawBuffers);

[greggman, 2013/03/08 21:48:28]

Same as above

[Zhenyao Mo, 2013/03/13 01:22:02]

Done.

+  for (GLsizei i = 0; i < n; ++i)
+    draw_buffers_[i] = bufs[i];
+}
+
 void Framebuffer::UnbindRenderbuffer(
     GLenum target, Renderbuffer* renderbuffer) {
   bool done;
@@ -456,10 +472,6 @@
 
 void Framebuffer::AttachRenderbuffer(
     GLenum attachment, Renderbuffer* renderbuffer) {
-  DCHECK(attachment == GL_COLOR_ATTACHMENT0 ||
-         attachment == GL_DEPTH_ATTACHMENT ||
-         attachment == GL_STENCIL_ATTACHMENT ||
-         attachment == GL_DEPTH_STENCIL_ATTACHMENT);
   const Attachment* a = GetAttachment(attachment);
   if (a)
     a->DetachFromFramebuffer();
@@ -475,10 +487,6 @@
 void Framebuffer::AttachTexture(
     GLenum attachment, Texture* texture, GLenum target,
     GLint level) {
-  DCHECK(attachment == GL_COLOR_ATTACHMENT0 ||
-         attachment == GL_DEPTH_ATTACHMENT ||
-         attachment == GL_STENCIL_ATTACHMENT ||
-         attachment == GL_DEPTH_STENCIL_ATTACHMENT);
   const Attachment* a = GetAttachment(attachment);
   if (a)
     a->DetachFromFramebuffer();