Implement EXT_draw_buffers WebGL extention support in command buffer.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
===================================================================
--- gpu/command_buffer/service/gles2_cmd_decoder.cc	(revision 186778)
+++ gpu/command_buffer/service/gles2_cmd_decoder.cc	(working copy)
@@ -870,6 +870,8 @@
 
   void DoTraceEndCHROMIUM(void);
 
+  void DoDrawBuffersEXT(GLsizei count, const GLenum* bufs);
+
   // Creates a Program for the given program.
   Program* CreateProgram(
       GLuint client_id, GLuint service_id) {
@@ -2518,7 +2520,7 @@
   resources.MaxTextureImageUnits = group_->max_texture_image_units();
   resources.MaxFragmentUniformVectors =
       group_->max_fragment_uniform_vectors();
-  resources.MaxDrawBuffers = 1;
+  resources.MaxDrawBuffers = group_->max_draw_buffers();
 
 #if (ANGLE_SH_VERSION >= 110)
   resources.FragmentPrecisionHigh = 1;
@@ -2533,6 +2535,8 @@
         features().arb_texture_rectangle ? 1 : 0;
     resources.OES_EGL_image_external =
         features().oes_egl_image_external ? 1 : 0;
+    resources.EXT_draw_buffers =
+        features().ext_draw_buffers ? 1 : 0;
   }
 
   ShShaderSpec shader_spec = force_webgl_glsl_validation_ ||
@@ -4022,6 +4026,44 @@
         params[0] = texture_manager()->MaxSizeForTarget(GL_TEXTURE_CUBE_MAP);
       }
       return true;
+    case GL_MAX_COLOR_ATTACHMENTS_EXT:
+      *num_written = 1;
+      if (params) {
+        params[0] = group_->max_color_attachments();
+      }
+      return true;
+    case GL_MAX_DRAW_BUFFERS_ARB:
+      *num_written = 1;
+      if (params) {
+        params[0] = group_->max_draw_buffers();
+      }
+      return true;
+    case GL_DRAW_BUFFER0_ARB:

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

If we're making this forward compatible it seems like rather than this being a
case it should be under default as in

   default:
     if (pname >= GL_DRAW_BUFFER0_ARB && 
         pname < GL_DRAW_BUFFER0_ARB + max_draw_buffers) {
       ...
       return true;
     }

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

Done.

+    case GL_DRAW_BUFFER1_ARB:
+    case GL_DRAW_BUFFER2_ARB:
+    case GL_DRAW_BUFFER3_ARB:
+    case GL_DRAW_BUFFER4_ARB:
+    case GL_DRAW_BUFFER5_ARB:
+    case GL_DRAW_BUFFER6_ARB:
+    case GL_DRAW_BUFFER7_ARB:
+    case GL_DRAW_BUFFER8_ARB:
+    case GL_DRAW_BUFFER9_ARB:
+    case GL_DRAW_BUFFER10_ARB:
+    case GL_DRAW_BUFFER11_ARB:
+    case GL_DRAW_BUFFER12_ARB:
+    case GL_DRAW_BUFFER13_ARB:
+    case GL_DRAW_BUFFER14_ARB:
+    case GL_DRAW_BUFFER15_ARB:
+      *num_written = 1;
+      if (params) {
+        Framebuffer* framebuffer =
+            GetFramebufferInfoForTarget(GL_FRAMEBUFFER);
+        if (framebuffer)
+          params[0] = framebuffer->GetDrawBuffer(pname);
+        else
+          NOTREACHED();
+      }
+      return true;
     case GL_ALPHA_BITS:
       *num_written = 1;
       if (params) {
@@ -9954,6 +9996,31 @@
   gpu_tracer_->End();
 }
 
+void GLES2DecoderImpl::DoDrawBuffersEXT(
+    GLsizei count, const GLenum* bufs) {
+  Framebuffer* framebuffer = GetFramebufferInfoForTarget(GL_FRAMEBUFFER);
+  if (framebuffer) {

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

framebuffer will be NULL if the current target is the backbuffer IIRC. You'll
need to do some other work here for the case where it's NULL. I'm guessing you
need to check that count/bufs is correct for the backbuffer. But then you need
to actually use GL_COLOR_ATTACHMENT0, GL_NONE etc since when it's not actually
the backbuffer.

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

Done.

+    if (count > static_cast<GLsizei>(group_->max_draw_buffers())) {
+      SetGLError(GL_INVALID_VALUE,
+                 "glDrawBuffersEXT", "greater than GL_MAX_DRAW_BUFFERS_EXT");
+      return;
+    }
+    for (GLsizei i = 0; i < count; ++i) {
+      if (bufs[i] != static_cast<GLenum>(GL_COLOR_ATTACHMENT0 + i) &&
+          bufs[i] != GL_NONE) {
+        SetGLError(GL_INVALID_OPERATION,
+                   "glDrawBuffersEXT",
+                   "bufs[i] not GL_NONE or GL_COLOR_ATTACHMENTi_EXT");
+        return;
+      }
+    }
+    framebuffer->SetDrawBuffers(count, bufs);
+    glDrawBuffersARB(count, bufs);
+  } else {
+    NOTREACHED();
+  }
+}
+
 bool GLES2DecoderImpl::ValidateAsyncTransfer(
     const char* function_name,
     Texture* info,