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 c30d501ed0aec6d20eee1c50a3aba65c70d9d5a7..6771f974a1d77c8b4c139393b9cfa7e42bc3c0e7 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -6005,7 +6005,28 @@ 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 ||
+      workarounds().do_decoder_encoder_srgb_generatemipmap) {

[piman, 2016/09/22 19:24:59]

Did you mean !workarounds().do_decoder_encoder_srgb_generatemipmap ?

[yizhou.jiang, 2016/09/26 00:56:32]

Done.

+    if (workarounds().do_decoder_encoder_srgb_generatemipmap) {

[piman, 2016/09/22 19:24:59]

This is probably incorrect too... Maybe the best way to explain the intent well
is to instead do:

if (feature_info_->feature_flags().desktop_srgb_support) {
  state_.EnableDisableFramebufferSRGB(enable_srgb);
}

[yizhou.jiang, 2016/09/26 00:56:32]

Done.

+      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(yizhou): If the target is GL_TEXTURE_3D or GL_TEXTURE_2D_ARRAY,
+      // 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