Add EXT_color_buffer_half_float extension support in GPU commandbuffer 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 396311cffb1b6690d7c84ff0a2052ebc885206e1..8425928e3e11a2ce8919e92f51551b43d6ca70a9 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -431,7 +431,6 @@ void FeatureInfo::AddFeatures(const CommandLine& command_line) {
     texture_format_validators_[GL_LUMINANCE].AddValue(GL_FLOAT);
     texture_format_validators_[GL_LUMINANCE_ALPHA].AddValue(GL_FLOAT);
     validators_.pixel_type.AddValue(GL_FLOAT);
-    validators_.read_pixel_type.AddValue(GL_FLOAT);
     AddExtensionString("GL_OES_texture_float");
     if (enable_texture_float_linear) {
       AddExtensionString("GL_OES_texture_float_linear");
@@ -445,13 +444,28 @@ void FeatureInfo::AddFeatures(const CommandLine& command_line) {
     texture_format_validators_[GL_LUMINANCE].AddValue(GL_HALF_FLOAT_OES);
     texture_format_validators_[GL_LUMINANCE_ALPHA].AddValue(GL_HALF_FLOAT_OES);
     validators_.pixel_type.AddValue(GL_HALF_FLOAT_OES);
-    validators_.read_pixel_type.AddValue(GL_HALF_FLOAT_OES);
     AddExtensionString("GL_OES_texture_half_float");
     if (enable_texture_half_float_linear) {
       AddExtensionString("GL_OES_texture_half_float_linear");
     }
   }
 
+  bool enable_color_buffer_half_float = false;
+  if (extensions.Contains("GL_ARB_color_buffer_float")
+    || extensions.Contains("GL_EXT_color_buffer_half_float")) {
+    if (enable_texture_half_float)
+      enable_color_buffer_half_float = true;
+  }
+  if (enable_color_buffer_half_float) {
+    validators_.render_buffer_format.AddValue(GL_RGBA16F_EXT);
+    validators_.render_buffer_format.AddValue(GL_RGB16F_EXT);
+    validators_.frame_buffer_parameter.AddValue(
+      GL_FRAMEBUFFER_ATTACHMENT_COMPONENT_TYPE_EXT);
+    validators_.read_pixel_type.AddValue(GL_HALF_FLOAT_OES);
+    validators_.read_pixel_type.AddValue(GL_FLOAT);

[Ken Russell (switch to Gerrit), 2013/07/10 02:14:24]

There's a general problem with this patch and the associated ANGLE one that it
combines EXT_color_buffer_half_float with rendering to and reading back from
FP32 targets. These must be split up. Another problem is that
http://www.khronos.org/registry/webgl/extensions/WEBGL_color_buffer_float/ is a
WebGL extension, but there's no underlying extension defined against OpenGL ES
2.0. EXT_color_buffer_float is defined against ES 3.0, so when ANGLE supports ES
3.0, it can just start supporting EXT_color_buffer_float.

I think the necessary path forward is:

 - Define an ANGLE_color_buffer_float extension (perhaps just in the ANGLE
repository; I don't see an advantage to pushing this up to Khronos at this
point, given that ES 3.0 is their focus)
 - Implement that in the current ANGLE
 - Expose two extensions here, EXT_color_buffer_half_float and
ANGLE_color_buffer_float
 - Later, in WebGLRenderingContext, expose WEBGL_color_buffer_float if the
underlying ANGLE_color_buffer_float extension is supported

What do you think?

+    AddExtensionString("GL_EXT_color_buffer_half_float");
+  }
+
   // Check for multisample support
   bool ext_has_multisample =
       extensions.Contains("GL_EXT_framebuffer_multisample");