[Mesa-dev] [PATCH 0/2] Allow redeclaration of GLSL builtins; fixes Dying Light and Dead Island Definitive Edition

[Samuel Pitoiset]

In an ideal world, I would prefer the compiler to be less strict for 
dump things like that, but it might require more work, so your solution 
is fine by me.

I can confirm this fixes Dying Light, not sure why we didn't find this 
before (we probably followed a wrong path), but it's a nice find. Thanks! :)

The "compat" issue is a different problem which should be investigated a 
bit more. Again, in an ideal world, I would like users to be able to 
launch the games without any overrides.

Cheers,
Samuel.

On 05/12/2017 03:39 PM, John Brooks wrote:
> Since release, Dying Light and Dead Island Definitive Edition have been broken
> on Mesa, producing at best only a black screen after loading. I found that the
> root of the problem is that their vertex shaders redeclare the GLSL builtin
> gl_VertexID, which Mesa's compiler considers to be an error:
> 
>      error: `gl_VertexID' redeclared
> 
> These patches make the compiler more lenient so that the shaders compile.
> Because such redeclarations are not explicitly valid in the spec, this
> behaviour is selectively activated by the new allow_glsl_builtin_redeclaration
> driconf option, which has been enabled for both games in the default drirc.
> 
> With this change, both games work on Mesa and render correctly. Note that the
> games require OpenGL 4.4+, and so it is necessary to launch them with
> MESA_GL_VERSION_OVERRIDE and MESA_GLSL_VERSION_OVERRIDE set to OpenGL 4.4 (GLSL
> 440) or higher.
> 
> Contrary to popular belief, this problem actually had nothing whatsoever to do
> with compatibility profiles. Forcing Mesa to create a higher version
> compatibility profile with MESA_GL_VERSION_OVERRIDE=4.5COMPAT or
> allow_higher_compat_version results in graphical glitches, so don't use that.
> 
> 
> A few extra notes for users reading this: I had terrible, unplayable
> performance with Dying Light on a configuration with an R9 290, Mesa 17.1-rc3,
> and the radeon kernel driver on kernel 4.10. Switching to the amdgpu driver
> (enable CONFIG_DRM_AMDGPU_CIK, blacklist radeon, install amdgpu DDX and set
> Driver "amdgpu" in xorg.conf) on kernel 4.11 made it playable.  With amdgpu it
> hovers around 25-35fps except in select areas (such as the Tower lobby and near
> Zere's trailer) near the start of the game where the framerate plummets for no
> apparent reason. Dead Island Definitive Edition performs much better in general
> than Dying Light, at least on amdgpu. I did not test DIDE on radeon. Ongoing
> TTM optimization work may mitigate the performance problems in the future.
> 
> 
> The main thing I'm unsure of is whether allowing GLSL builtin redeclarations
> should be a driconf option or default behaviour. I looked through the GLSL spec
> and initially thought that such redeclarations were permitted because of this
> line from page 66 of <https://khronos.org/registry/OpenGL/specs/gl/GLSLangSpec.4.50.pdf>:
> 
>      in vec4 gl_FragCoord; // redeclaration that changes nothing is allowed
> 
> But others on IRC interpreted it as referring only to gl_FragCoord, which I
> agree would make sense given the context. So to be on the safe side I made it
> conditional on a driconf option. I leave the final decision to the reviewers.
> Let me know what you think.
> 
> Thank you to to funfunctor, notaz, and others from the #radeon IRC channel for
> their suggestions and their help with analyzing the game binaries.
> 
> --
> John Brooks
> Frogging101 on IRC and elsewhere
>