3dfx never had a full OpenGL implementation until the Voodoo 4/5's came around if I'm not mistaken, 3dfx had MiniGL though. which I "think" Half-Life/Counter-Strike indeed support, along with Direct3D ...

For OpenGL 2 capable hardware, these new extensions are provided: * ARB_texture_swizzle (also in core OpenGL 3.3) * ARB_sampler_objects (also in core OpenGL 3.3) * ARB_occlusion_query2 (also in core ...