It has nothing to do with Black Mesa (this is not Black Mesa).Mesa3D drivers are open-source graphics drivers that implement APIs like OpenGL, Vulkan, OpenCL, and Direct3D (via Gallium) on Windows, Linux and other platforms. If your system has no proper GPU drivers installed or the hardware is unsupported, Mesa can provide software-based OpenGL rendering (via llvmpipe or softpipe).
https://github.com/pal1000/mesa-dist-win