command_buffer: MAX/BASE_LEVEL fixes for GetTexParameter

gpu/command_buffer/service/gles2_cmd_decoder.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/gles2_cmd_decoder.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
@@ skipping 9252 matching lines @@
       if (feature_info_->gl_version_info().IsLowerThanGL(4, 2)) {
         GLint levels = texture->GetImmutableLevels();
         if (fparams) {
           fparams[0] = static_cast<GLfloat>(levels);
         } else {
           iparams[0] = levels;
         }
         return;
       }
       break;
+    // Get the level information from the texture to avoid a Mac driver
+    // bug where they store the levels in int16_t, making values bigger
+    // than 2^15-1 overflow in the negative range.

[Zhenyao Mo, 2016/05/27 22:33:44]

Could you put this code behind a workaround? say, use_shadowed_tex_params?

This way we can turn it off and show driver vendors their bugs.

+    case GL_TEXTURE_BASE_LEVEL:
+      if (fparams) {
+        fparams[0] = static_cast<GLfloat>(texture->base_level());
+      } else {
+        iparams[0] = texture->base_level();
+      }
+      return;
+    case GL_TEXTURE_MAX_LEVEL:
+      if (fparams) {
+        fparams[0] = static_cast<GLfloat>(texture->max_level());
+      } else {
+        iparams[0] = texture->max_level();
+      }
+      return;
     default:
       break;
   }
   if (fparams) {
     glGetTexParameterfv(target, pname, fparams);
   } else {
     glGetTexParameteriv(target, pname, iparams);
   }
 }
 
@@ skipping 7542 matching lines @@
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "base/macros.h"
 #include "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu