emulate srgb format for generateMipmap

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 5987 matching lines @@
       target == GL_TEXTURE_2D) {
     if (base_level != 0 &&
         !tex->GetLevelType(target, 0, &type, &internal_format) &&
         tex->GetLevelType(target, tex->base_level(), &type, &internal_format)) {
       format = TextureManager::ExtractFormatFromStorageFormat(internal_format);
       glTexImage2D(target, 0, internal_format, 1, 1, 0, format, type, nullptr);
       texture_zero_level_set = true;
     }
   }
 
-  glGenerateMipmapEXT(target);
+  tex->GetLevelType(target, 0, &type, &internal_format);
+  bool enable_srgb =
+      GetColorEncodingFromInternalFormat(internal_format) == GL_SRGB;
+  if (!enable_srgb || !feature_info_->feature_flags().desktop_srgb_support ||
+      gl_version_info().IsAtLeastGL(4, 4)) {

[piman, 2016/09/20 21:53:30]

Is there any particular reason to cut-off at GL 4.4? Nothing in the spec really
differs between 4.3 and 4.4 (or 4.2 or 4.5 really). Is this something that
should be treated as a bug workaround, so that we can have more flexibility
about targeting the problematic drivers?

[yizhou.jiang, 2016/09/21 08:59:22]

According to BlitFramebuffer and drawArrays api, when processing srgb format and
opengl version under 4.4, they also have to do decoder and encoder. when version
is over 4.4, these api work well without this workaround.
In addition, qiankun has tested generateMipmap api on Nvidia, opengl 4.5, and it
also works well without modifying the code. We suppose that mesa team is working
on a patch which would fix this problem over 4.4. So I put an version condition
here. 

[piman, 2016/09/21 23:45:32]

It seems somewhat orthogonal - the behavior of glGenerateMipmaps for sRGB (not
fully specified in any case) doesn't really mention either one of
glBlitFramebuffer or glDrawArrays. From the bug, it sounds like we're
experiencing driver differences, and those are best handled with workaround
entries, which can precisely target problematic drivers/hardware without making
the code convoluted.

I am ok if that workaround entry starts with targeting desktop GL before 4.4,
but we can refine as we test more hardware/drivers.

+    if (gl_version_info().IsAtLeastGL(4, 4)) {
+      state_.EnableDisableFramebufferSRGB(enable_srgb);
+    }
+    glGenerateMipmapEXT(target);
+  } else {
+    if (target == GL_TEXTURE_2D) {
+      state_.EnableDisableFramebufferSRGB(true);
+      if (!InitializeSRGBConverter("generateMipmap")) {
+        return;
+      }
+      srgb_converter_->SRGBGenerateMipmap(this, tex, target);
+    } else {  // TODO If the target is GL_TEXTURE_3D or GL_TEXTURE_2D_ARRAY,

[Ken Russell (switch to Gerrit), 2016/09/21 01:00:14]

Should be TODO(yizhao.jiang) or TODO(yizhao). Also please put comment on a new
line.

[yizhou.jiang, 2016/09/21 08:59:22]

Done.

+              // this change can not generate correct mipmap.
+      glGenerateMipmapEXT(target);
+    }
+  }
 
   if (texture_zero_level_set) {
     // This may have some unwanted side effects, but we expect command buffer
     // validation to prevent you from doing anything weird with the texture
     // after this, like calling texSubImage2D sucessfully.
     glTexImage2D(target, 0, internal_format, 0, 0, 0, format, type, nullptr);
   }
 
   if (workarounds().set_texture_filter_before_generating_mipmap) {
     glTexParameteri(target, GL_TEXTURE_MIN_FILTER,
@@ skipping 12056 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