#rev 2020-09-02 davidsch
#rev 2018-08-28 davidsch

= OpenGL =

== Compiling OpenGL/ NVidia CUDA-based applications on Debian Linux ==
The Debian platform managed by ISG D-ITET uses the following directory layout for the OpenGL libraries and headers:

=== Libraries ===
 * The `/usr/lib/x86_64-linux-gnu/libGL*.so` OpenGL libraries are symbolic links to the hardware-specific libraries. There is a mechanism in the startup process of each client workstation which detects the accurate OpenGL library based on the information about the graphics card and the kernel driver. The CUDA runtime libraries are found in the same directory.

=== OpenGL header files ===
The OpenGL headers are found under `/usr/include/GL`.

=== CUDA header files ===
For NVidia programming, a CUDA toolkit matching the installed NVidia driver is selected when a toolkit program like `nvcc`is run.<<BR>>
Any CUDA headers have to bee included by manually matching the toolkit version used. Check the content of the SEPP package [[https://www.sepp.ee.ethz.ch/sepp-debian/cuda_toolkit-1x.x-sr.html|cuda_toolkit-1x.x-sr]] for available versions by listing its contents with `ls /usr/pack/cuda_toolkit-1x.x-sr`

Usually, there is a lower driver/toolkit version combo for desktop PCs and a higher version combo for Slurm GPU nodes:
 * For desktop PCs: driver version `418` works with toolkit version `10.1.243`
 * For Slurm GPU nodes: driver version `470` works with toolkit version `11.4.4`

The following environment variables have to be set with the correct driver or toolkit version:
{{{#!highlight bash numbers=disable
export CPPFLAGS='-I/usr/pack/cuda_toolkit-1x.x-sr/<driver or toolkit version>/include'`
export LDFLAGS='-L/usr/pack/cuda_toolkit-1x.x-sr/<driver or toolkit version>/lib64 -Wl,-rpath,/usr/pack/cuda_toolkit-1x.x-sr/<driver or toolkit version>/lib64' `
}}}

=== Compiling sources and linking against NVidia libraries ===
 * Make sure no special `CPPFLAGS` and `LDFLAGS` are set. The required headers and libraries are all found under the standard system paths. If you use your own OpenGL/ CUDA toolkit, e.g. installed in your home, make sure it is compatible with the graphics driver/ hardware installed on the system. Note: if you don't have brand new hardware in your computer, the most current CUDA release most probably won't work with it - use an older relase or ask ISG D-ITET if you are in doubt about the right version.
 * Then set `CPPFLAGS` (for the C preprocessor used by most compilers) and `LDFLAGS` (linker flags) as follows:

 Assuming you installed the toolkit under `/home/$USER/toolkit` you set the mentioned environment variables in your Debian shell (`bash`, `tcsh`, ...) as follows, before you start compiling/ linking:
 {{{#!highlight bash numbers=disable
export CPPFLAGS="-I/home/$USER/toolkit/include"
export LDFLAGS="-L/home/$USER/toolkit/lib -Wl,-rpath,/home/$USER/toolkit/lib"
}}}
 `$USER` must of course be replaced with your ETH (login-)username.

=== Recomendation ===
That said we encourage the use of CUDA Toolkit within Conda environments. More details can be found in the [[Programming/Languages/GPUCPU|Working with GPU or CPU in data sciences]] and [[Programming/Languages/Conda|Conda]] subpages of this wiki.

----
[[CategoryLXSW]]