Move the WebGL DrawBuffers support check to the command buffer service.

gpu/command_buffer/service/feature_info.cc

Index: gpu/command_buffer/service/feature_info.cc
diff --git a/gpu/command_buffer/service/feature_info.cc b/gpu/command_buffer/service/feature_info.cc
index a8b497fd6f5ad735068aab7e5f119b932894f3d7..6ea1adf01ba910eee917bad1d6b48e2452371007 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -106,6 +106,102 @@ class ScopedPixelUnpackBufferOverride {
     GLint orig_binding_;
 };
 
+bool IsWebGLDrawBuffersSupported(bool has_depth_texture,
+                                 bool has_depth_stencil_texture) {
+  // This is called after we make sure GL_EXT_draw_buffers is supported.
+
+  GLint fb_binding = 0;
+  GLint tex_binding = 0;
+  glGetIntegerv(GL_FRAMEBUFFER_BINDING, &fb_binding);
+  glGetIntegerv(GL_TEXTURE_BINDING_2D, &tex_binding);
+
+  GLint max_draw_buffers = 0;
+  GLint max_color_attachments = 0;
+  glGetIntegerv(GL_MAX_DRAW_BUFFERS, &max_draw_buffers);
+  glGetIntegerv(GL_MAX_COLOR_ATTACHMENTS, &max_color_attachments);
+  if (max_draw_buffers < 4 || max_color_attachments < 4)
+    return false;
+
+  GLuint fbo;
+  glGenFramebuffersEXT(1, &fbo);
+  glBindFramebufferEXT(GL_FRAMEBUFFER, fbo);
+
+  GLuint depth_stencil = 0;
+  if (has_depth_stencil_texture) {
+    glGenTextures(1, &depth_stencil);
+    glBindTexture(GL_TEXTURE_2D, depth_stencil);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_STENCIL, 1, 1, 0, GL_DEPTH_STENCIL,

[Zhenyao Mo, 2017/02/23 00:12:43]

Juts want to make sure this (unsized internal format) gets translated before
sending down to the driver (in the binding)

I am not sure if the translation happens in command buffer or in the binding. 
The blink side code goes through both and now we only go through the binding.

[Ken Russell (switch to Gerrit), 2017/02/23 01:46:26]

I don't remember exactly at this point -- but grepping through src/ui/gl/ it
looks like no translation of this value is done in the bindings layer. So we do
need to be very careful about not generating INVALID_OPERATION errors on real ES
3.0 implementations, for example.

+                 GL_UNSIGNED_INT_24_8, nullptr);
+  }
+
+  GLuint depth = 0;
+  if (has_depth_texture) {
+    glGenTextures(1, &depth);
+    glBindTexture(GL_TEXTURE_2D, depth);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, 1, 1, 0,

[Zhenyao Mo, 2017/02/23 00:12:43]

Same here.

+                 GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, nullptr);
+  }
+
+  GLint max_allowed_buffers = std::min(max_draw_buffers, max_color_attachments);
+  std::vector<GLuint> colors(max_allowed_buffers, 0);
+  glGenTextures(max_allowed_buffers, colors.data());
+
+  bool result = true;
+  for (GLint i = 0; i < max_allowed_buffers; ++i) {
+    GLint color = colors[i];
+    glBindTexture(GL_TEXTURE_2D, color);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE,
+                 nullptr);
+    glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i,
+                              GL_TEXTURE_2D, color, 0);
+    if (glCheckFramebufferStatusEXT(GL_FRAMEBUFFER) !=
+        GL_FRAMEBUFFER_COMPLETE) {
+      result = false;
+      break;
+    }
+    if (has_depth_texture) {
+      glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
+                                GL_TEXTURE_2D, depth, 0);
+      if (glCheckFramebufferStatusEXT(GL_FRAMEBUFFER) !=
+          GL_FRAMEBUFFER_COMPLETE) {
+        result = false;
+        break;
+      }
+      glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
+                                GL_TEXTURE_2D, 0, 0);
+    }
+    if (has_depth_stencil_texture) {
+      // For ES 2.0 contexts DEPTH_STENCIL is not available natively, so we
+      // emulate it at the command buffer level for WebGL contexts.
+      glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT,
+                                GL_TEXTURE_2D, depth_stencil, 0);
+      if (glCheckFramebufferStatusEXT(GL_FRAMEBUFFER) !=
+          GL_FRAMEBUFFER_COMPLETE) {
+        result = false;
+        break;
+      }
+      glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT,
+                                GL_TEXTURE_2D, 0, 0);
+    }
+  }
+
+  glBindFramebufferEXT(GL_FRAMEBUFFER, static_cast<GLuint>(fb_binding));
+  glDeleteFramebuffersEXT(1, &fbo);
+
+  glBindTexture(GL_TEXTURE_2D, static_cast<GLuint>(tex_binding));
+  if (has_depth_texture) {
+    glDeleteTextures(1, &depth);
+  }
+  if (has_depth_stencil_texture) {
+    glDeleteTextures(1, &depth_stencil);
+  }
+  glDeleteTextures(colors.size(), colors.data());
+
+  DCHECK(glGetError() == GL_NO_ERROR);
+
+  return result;
+}
+
 }  // anonymous namespace.
 
 FeatureInfo::FeatureFlags::FeatureFlags() {}
@@ -468,6 +564,7 @@ void FeatureInfo::InitializeFeatures() {
         GL_DEPTH_COMPONENT);
   }
 
+  bool enable_depth_stencil_texture = false;
   if (extensions.Contains("GL_EXT_packed_depth_stencil") ||
       extensions.Contains("GL_OES_packed_depth_stencil") ||
       gl_version_info_->is_es3 ||
@@ -475,6 +572,7 @@ void FeatureInfo::InitializeFeatures() {
     AddExtensionString("GL_OES_packed_depth_stencil");
     feature_flags_.packed_depth24_stencil8 = true;
     if (enable_depth_texture) {
+      enable_depth_stencil_texture = true;
       validators_.texture_internal_format.AddValue(GL_DEPTH_STENCIL);
       validators_.texture_format.AddValue(GL_DEPTH_STENCIL);
       validators_.pixel_type.AddValue(GL_UNSIGNED_INT_24_8);
@@ -1161,10 +1259,14 @@ void FeatureInfo::InitializeFeatures() {
       extensions.Contains("GL_EXT_draw_buffers");
   bool can_emulate_es2_draw_buffers_on_es3_nv =
       gl_version_info_->is_es3 && extensions.Contains("GL_NV_draw_buffers");
-  bool have_es2_draw_buffers = !workarounds_.disable_ext_draw_buffers &&
-                               IsWebGL1OrES2Context() &&
-                               (have_es2_draw_buffers_vendor_agnostic ||
-                                can_emulate_es2_draw_buffers_on_es3_nv);
+  bool have_es2_draw_buffers =
+      !workarounds_.disable_ext_draw_buffers &&
+      (have_es2_draw_buffers_vendor_agnostic ||
+       can_emulate_es2_draw_buffers_on_es3_nv) &&
+      (context_type_ == CONTEXT_TYPE_OPENGLES2 ||
+       (context_type_ == CONTEXT_TYPE_WEBGL1 &&
+        IsWebGLDrawBuffersSupported(enable_depth_texture,
+                                    enable_depth_stencil_texture)));
   if (have_es2_draw_buffers) {
     AddExtensionString("GL_EXT_draw_buffers");
     feature_flags_.ext_draw_buffers = true;