Tentative fix for FindOptiX.cmake

[roncapat]

Lost some hours to fix gz_rendering build warnings about missing dependency OptiX only to find out in gazebosim/gz-rendering#1010 that basically that renderer is ancient/broken... nevertheless, I think it would be good to leave here the bit and bolts that I discovered to be issue in my setup for OptiX discovery.

First of all, on Ubuntu 22.04 the library name is libnvoptix.so.1 while this script currently searches for liboptix.so or liboptix.1.so, so the lookup would always fail IMHO.

Secondly, but it can be my fault, I tried setting:

• --cmake-args OPTIX_INSTALL_DIR=path
• --cmake-args OptiX_INSTALL_DIR=path
• export OPTIX_INSTALL_DIR=path

but the include files were never detected. I solved the hard way by directly checking the $env var in find_path call.

[j-rivero]

Thanks for the PR ! Are you interested into having the support in place even the rendering code can be broken with current versions?

Looking into the code:

set(OptiX_INSTALL_DIR "$ENV{OPTIX_INSTALL_DIR}" CACHE PATH "Path to OptiX installed location.")

Should be getting th OPTIX_INSTALL_DIR enviroment variable and put that in the correct place. In the worst case, I'm fine if we change all the ocurrences from OptiX_INSTALL_DIR to $ENV{OPTIX_INSTALL_DIR} but please be sure to delete the CMakeCache.txt and run the thing to check if the existing code is really working.