Use GLSL version 100 for OpenGL context versions prior to 3.2.

gpu/command_buffer/service/shader_translator.cc

Index: gpu/command_buffer/service/shader_translator.cc
diff --git a/gpu/command_buffer/service/shader_translator.cc b/gpu/command_buffer/service/shader_translator.cc
index 255caffc691d95efea9cb22c4cae85d0991ea263..8d89ec99fd674ab277a83dcd5380a42557435940 100644
--- a/gpu/command_buffer/service/shader_translator.cc
+++ b/gpu/command_buffer/service/shader_translator.cc
@@ -141,15 +141,15 @@ ShShaderOutput ShaderTranslator::GetShaderOutputLanguageForContext(
     return SH_GLSL_330_CORE_OUTPUT;
   } else if (context_version == 320) {
     return SH_GLSL_150_CORE_OUTPUT;

[Kimmo Kinnunen, 2015/12/18 07:03:23]

Would version 150 also have the same problem?

https://www.opengl.org/registry/doc/GLSLangSpec.1.50.11.pdf still has that "can
only be indexed with integral constant expressions"...

[Ken Russell (switch to Gerrit), 2015/12/22 02:45:18]

Looking more deeply, yes, it looks like this restriction wasn't lifted until
OpenGL 4.0. However, for some reason, it's only Intel's driver that seems to
enforce it. Both NVIDIA's and AMD's drivers compile these sampler array indexing
expressions without complaint. I'm not sure whether that's because they are
using the compatibility profile, which didn't exist until OpenGL 3.2. Intel's
drivers on Linux seem to default to using OpenGL 3.0 at the latest.

-  } else if (context_version == 310) {
-    return SH_GLSL_140_OUTPUT;
-  } else if (context_version == 300) {
-    return SH_GLSL_130_OUTPUT;
   }
 
-  // Before OpenGL 3.0 we use compatibility profile. Also for future
-  // specs between OpenGL 3.3 and OpenGL 4.0, at the time of writing,
-  // we use compatibility profile.
+  // Before OpenGL 3.2 we use the compatibility profile. Shading
+  // language version 130 restricted how sampler arrays can be indexed
+  // in loops, which causes problems like crbug.com/550487 .

[Kimmo Kinnunen, 2015/12/18 07:03:23]

Just verifying: so not using 130-150 would be a workaround for ANGLE not being
able to translate WebGL SL to GLSL version 130-150? Or fundamental issue that
WebGL SL can not be supported with 130-150?

[Ken Russell (switch to Gerrit), 2015/12/22 02:45:18]

OpenGL ES 2.0 / WebGL 1.0 require sampler arrays to be indexable with a
constant-index-expression, which strictly speaking isn't supported by the
desktop OpenGL shading language between versions 130 and 330, inclusive. It's a
fundamental problem with the OpenGL shading language spec, but for some reason,
only some drivers enforce it.

+  //
+  // Also for any future specs that might be introduced between OpenGL
+  // 3.3 and OpenGL 4.0, at the time of writing, we use the
+  // compatibility profile.
   return SH_GLSL_COMPATIBILITY_OUTPUT;
 }