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

[Timothy Arceri]

On 13/05/17 09:55, John Brooks wrote:
> On Sat, May 13, 2017 at 09:04:05AM +1000, Timothy Arceri wrote:
>> On 13/05/17 00:11, John Brooks wrote:
>>> On Fri, May 12, 2017 at 03:56:26PM +0200, Samuel Pitoiset wrote:
>>>>
>>>>
>>>> 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.
>>>>
>>>> I wonder if there is multiple versions of Dying Light, but using
>>>> MESA_GL_VERSION_OVERRIDE=4.4 and MESA_GLSL_VERSION_OVERRIDE=440 doesn't work
>>>> for me (game crash at launching). Also it requests some unsupported GL
>>>> functions (compat?).
>>>>
>>>> IIRC, Dying Light wants a GL 4.4 compat profile, I guess Timothy can
>>>> confirm?
>>>>
>>>> What's your steam app ID?
>>>>
>>>> Btw, you probably don't need to override the GL/GLSL versions, it should be
>>>> backward compatible.
>>>>
>>>
>>> Steam App ID 239140. The use of legacy functions (such as glBegin) in frame 0
>>> is SDL's doing:
>>> <https://github.com/spurious/SDL-mirror/blob/master/src/render/opengl/SDL_render_gl.c#L1334>
>>>
>>> I don't know why your game would crash on launch. My first thought would be
>>> steam runtime issues though. Make sure Steam runtime is enabled and remove
>>> ~/.local/share/Steam/ubuntu12_32/steam-runtime/amd64/usr/lib/x86_64-linux-gnu/libstdc++.so.6
>>>
>>> The version override is necessary since the game will not render at all with a
>>> 3.0 compat profile, which is what it gets without an override.
>>
>> Right but isn't that is because the game is requesting a compat profile?
>>
>> How do you know that the rendering issues you see when using the compat
>> override are not because of missing compat support for higher GL versions?
>>
>> For example a feature/behavior supported in an eariler GL version may have
>> been changed to be more like core and it just happens that overriding to use
>> core makes the rendering problems go away.
>>
> 
> Nope, it's not requesting a compat profile or anything specific at all. I
> checked with ltrace and the game calls SDL_GL_CreateContext without calling
> SDL_GL_SetAttribute to specify a version or type. Thus, SDL just calls
> glXCreateContext:
> https://hg.libsdl.org/SDL/file/tip/src/video/x11/SDL_x11opengl.c#l620 >
> The spec says nothing of what version you're supposed to get with
> glXCreateContext, but the result with Mesa is a 3.0 compatibility profile
> unless you override it.

That's because glXCreateContext is from a time before there was such a 
thing as compat profiles. glXCreateContextAttribsARB was introduced to 
solve this problem.

Are you suggesting other drivers don't return a compat profile in this 
scenario?

> 
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> 
> --
> John Brooks
> Frogging101 on IRC and elsewhere
>