emulate srgb format for generateMipmap

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 8ae668f5d7615483b9a024a4df8a7122f2d5b8d8..8aef983b322ee579fa93849b9ff4e0de132e6756 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -6005,7 +6005,27 @@ void GLES2DecoderImpl::DoGenerateMipmap(GLenum target) {
     }
   }
 
-  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