OpenGL
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This article or section is a candidate for merging with Mesa.
Notes: Most of the content here is related to the mesa package (Discuss in Talk:OpenGL#)
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You can enable OpenGL by setting hardware.graphics.enable = true;[note 1] in your /etc/nixos/configuration.nix.
OpenGL must break purity due to the need for hardware-specific linkage. Intel, AMD, and Nvidia have different drivers for example. On NixOS, these libraries are symlinked under
/run/opengl-driver/lib
and optionally (if hardware.graphics.enable32Bit[note 2] is enabled)
/run/opengl-driver-32/lib
When a program is installed in your environment, these libraries should be found automatically. However, this is not the case in a `nix-shell`. To fix, add this line to your shell.nix:
LD_LIBRARY_PATH="/run/opengl-driver/lib:/run/opengl-driver-32/lib";
Testing Mesa updates
To avoid a lot of rebuilds there's an internal NixOS option to override the Mesa drivers: hardware.opengl.package
It can be used like this:
hardware.opengl.package = (import /srv/nixpkgs-mesa { }).pkgs.mesa.drivers;
However, since Mesa 21.0.2 this doesn't necessarily work anymore and something like the following might be required:
system.replaceRuntimeDependencies = [
({ original = pkgs.mesa; replacement = (import /srv/nixpkgs-mesa { }).pkgs.mesa; })
({ original = pkgs.mesa.drivers; replacement = (import /srv/nixpkgs-mesa { }).pkgs.mesa.drivers; })
];
Note: Both of these approaches are impure and only work to a certain degree (many limitations!). If you want to use a different version of Mesa your best option is to use an overlay or a Git worktree where you use the same Nixpkgs revision and only alter pkgs/development/libraries/mesa/ for one of the two approaches mentioned above.
Debugging Mesa issues
There are a lot of useful environment variables for debugging purposes: https://docs.mesa3d.org/envvars.html
The most important one is LIBGL_DEBUG=verbose and helps with debugging error like:
libGL error: MESA-LOADER: failed to open $DRIVER (search paths /run/opengl-driver/lib/dri) libGL error: failed to load driver: $DRIVER
glxinfo
Use glxinfo to load 3D acceleration debug information.
If glxinfo returns Error: couldn't find RGB GLX visual or fbconfig, ensure you have hardware.opengl.extraPackages = [ pkgs.mesa.drivers ]; set.