gpu: support immutable texture on Linux Mesa driver and GLES3.

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 e58e6c21fc7b0afaa76c230f716566c9907120cf..bddffdeff1b524cc383b9b7f65c6762f6bd73729 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -395,10 +395,12 @@ void FeatureInfo::InitializeFeatures() {
   bool enable_texture_format_bgra8888 = false;
   bool enable_read_format_bgra = false;
   bool enable_render_buffer_bgra = false;
+  bool enable_immutable_texture_format_bgra =
+      extensions.Contains("GL_APPLE_texture_format_BGRA8888");
 
   // Check if we should allow GL_EXT_texture_format_BGRA8888
   if (extensions.Contains("GL_EXT_texture_format_BGRA8888") ||
-      extensions.Contains("GL_APPLE_texture_format_BGRA8888") ||
+      enable_immutable_texture_format_bgra ||
       extensions.Contains("GL_EXT_bgra")) {
     enable_texture_format_bgra8888 = true;
   }
@@ -691,7 +693,12 @@ void FeatureInfo::InitializeFeatures() {
     validators_.texture_parameter.AddValue(GL_TEXTURE_USAGE_ANGLE);
   }
 
-  if (extensions.Contains("GL_EXT_texture_storage")) {
+  // Only APPLE_texture_format_BGRA8888 extension allows BGRA8_EXT in ES3's
+  // glTexStorage2D.
+  enable_immutable_texture_format_bgra &= is_es3;

[piman, 2014/08/26 19:06:29]

nit: modifying this variable is hard to follow. How about simply testing
(enable_immutable_texture_format_bgra && is_es3) in the if below?

+  if (extensions.Contains("GL_EXT_texture_storage") ||
+      extensions.Contains("GL_ARB_texture_storage") ||

[piman, 2014/08/26 19:06:29]

So, GL_ARB_texture_storage doesn't by itself allow GL_BGRA8 to be passed, at
least in GLES. I'm not fully sure about desktop GL, where the rules on internal
formats are different than the ES rules, but GL_BGRA8 isn't anywhere in OpenGL
2.0 spec (even though it does have GL_EXT_bgra folded in).

[dshwang, 2014/08/26 19:24:04]

Linux mesa GL driver on both desktop and chromebook supports
GL_ARB_texture_storage and works very well with GL_BGRA8 by GL_EXT_bgra

If GL_ARB_texture_storage is in trouble on GLES, GL_EXT_texture_storage is
supposed to be in trouble also although there are not any GLES1/2 devices
supporting GL_EXT_texture_storage yet, because currently chromium is fine.

I'll block all ES devices unless supporting GL_APPLE_texture_format_BGRA8888

+      enable_immutable_texture_format_bgra) {
     feature_flags_.ext_texture_storage = true;
     AddExtensionString("GL_EXT_texture_storage");
     validators_.texture_parameter.AddValue(GL_TEXTURE_IMMUTABLE_FORMAT_EXT);