Implement EXT_draw_buffers WebGL extention support in command buffer.

gpu/command_buffer/service/context_group.cc

Index: gpu/command_buffer/service/context_group.cc
===================================================================
--- gpu/command_buffer/service/context_group.cc	(revision 187725)
+++ gpu/command_buffer/service/context_group.cc	(working copy)
@@ -46,6 +46,8 @@
       max_fragment_uniform_vectors_(0u),
       max_varying_vectors_(0u),
       max_vertex_uniform_vectors_(0u),
+      max_color_attachments_(1u),
+      max_draw_buffers_(1u),
       program_cache_(NULL),
       feature_info_(new FeatureInfo()) {
   {
@@ -100,9 +102,18 @@
     glGetIntegerv(GL_MAX_SAMPLES, &max_samples);
   }
 
+  if (feature_info_->feature_flags().ext_draw_buffers) {
+    GetIntegerv(GL_MAX_COLOR_ATTACHMENTS_EXT, &max_color_attachments_);
+    if (max_color_attachments_ < 1)
+      max_color_attachments_ = 1;
+    GetIntegerv(GL_MAX_DRAW_BUFFERS_ARB, &max_draw_buffers_);
+    if (max_draw_buffers_ < 1)
+      max_draw_buffers_ = 1;
+  }
+
   buffer_manager_.reset(new BufferManager(
       memory_tracker_, feature_info_.get()));
-  framebuffer_manager_.reset(new FramebufferManager());
+  framebuffer_manager_.reset(new FramebufferManager(max_draw_buffers_));
   renderbuffer_manager_.reset(new RenderbufferManager(memory_tracker_,
                                                       max_renderbuffer_size,
                                                       max_samples));
@@ -205,6 +216,13 @@
   }
 
   decoders_.push_back(base::AsWeakPtr<GLES2Decoder>(decoder));
+
+  DCHECK_GT(max_draw_buffers_, 0u);
+  draw_buffers_.reset(new GLenum[max_draw_buffers_]);
+  draw_buffers_[0] = GL_BACK;
+  for (uint32 i = 1; i < max_draw_buffers_; ++i)
+    draw_buffers_[i] = GL_NONE;
+
   return true;
 }
 
@@ -330,5 +348,18 @@
   return result;
 }
 
+GLenum ContextGroup::GetDrawBuffer(GLenum draw_buffer) const {
+  GLsizei index = static_cast<GLsizei>(
+      draw_buffer - GL_DRAW_BUFFER0_ARB);
+  DCHECK(index >= 0 && index < static_cast<GLsizei>(max_draw_buffers_));
+  return draw_buffers_[index];
+}
+
+void ContextGroup::SetDrawBuffers(GLsizei n, const GLenum* bufs) {
+  DCHECK(n <= static_cast<GLsizei>(max_draw_buffers_));
+  for (GLsizei i = 0; i < n; ++i)
+    draw_buffers_[i] = bufs[i];
+}
+
 }  // namespace gles2
 }  // namespace gpu