Witcher

So, how are you able to use Vulkan with The Witcher 2? I'm on Linux Mint and recently installed the Linux version from GOG, but my only renderer options are OpenGL 2.1 or 3.2. Are you playing this on Windows through SteamPlay or what? I saw the title and was hoping for an explanation or tutorial or something, but I haven't heard one yet.
- HickoryDickory86