Bug 99995

One difference is that 17.0 has GL 4.3 enabled for Maxwell (e.g. GTX 750), which perhaps causes the game to choose a different path, thus not really be directly comparable. Try it with

MESA_GL_VERSION_OVERRIDE=4.1

which will get it back to the same GL version that was available with 13.0. Or try it with

MESA_EXTENSION_OVERRIDE='-GL_ARB_shader_image_load_store -GL_ARB_compute_shader'

Maybe related:
With higher GL versions, Dirt enables "advanced lighting" options in the graphics menu. Setting this to "On" makes the game basically a slide show. But Im on a Radeon HD 7970. Also all other Radeon cards have a performance problem:
http://www.phoronix.com/scan.php?page=article&item=mesa171-pro60-rx470&num=2

where figures looked better in 2015:
http://www.phoronix.com/scan.php?page=article&item=dirt-showdown-linux&num=3

Some more infos about the lightning options:
http://www.rage3d.com/articles/gaming/codemaster_dirt_showdown_tech_review/index.php?p=2

(In reply to Ilia Mirkin from comment #1)

> One difference is that 17.0 has GL 4.3 enabled for Maxwell (e.g. GTX 750),
> which perhaps causes the game to choose a different path, thus not really be
> directly comparable. Try it with
> 
> MESA_GL_VERSION_OVERRIDE=4.1

If I export this before opening steam, steam causes a segfault


> Or try it with
> 
> MESA_EXTENSION_OVERRIDE='-GL_ARB_shader_image_load_store
> -GL_ARB_compute_shader'

If I try this, game loads smooth and works about 45fps, better than with mesa 13



(In reply to Gregor Münch from comment #2)
>With higher GL versions, Dirt enables "advanced lighting" options in the graphics menu.
At least for me, it is there, but Off in all the tests

The speed improvement on Maxwell is expected - Mesa 17.0 starts to add proper shader instruction scheduling information. In various tests it has improved overall perf ~2x (varies a lot based on how shader-computation-limited the software is, vs memory bandwidth-limited).

(In reply to Ilia Mirkin from comment #4)
> The speed improvement on Maxwell is expected - Mesa 17.0 starts to add
> proper shader instruction scheduling information. In various tests it has
> improved overall perf ~2x (varies a lot based on how
> shader-computation-limited the software is, vs memory bandwidth-limited).

I know :)
But I dont know why I have to "workaround" mesa this way to play, maybe there are lot of people that not know this too and it are with mesa 17..

Just want to add, using:

MESA_EXTENSION_OVERRIDE='-GL_ARB_shader_image_load_store -GL_ARB_compute_shader'

Makes the advanced lightning options disappear in the options.

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