The non-SDL port was one version I had when I started to build the project. Probably with mutated sources from some Q3 engine.

Pretty much it just loaded the menu screen and crashed down the line as it needed more work.

It is long buried in some forgotten dir now.

Question to my memory is if those versions (non-SDL vs SDL) were "different": At that time all I had were glitches at the first level and luck to start the game.

As experiment, one path to take is bypass opengl includes (that call SDL2 stubs) and inline the functions needed and see what happens "today". I did it time ago in some of the render code but didn't find anything special for performance.

I thought about a new non-sdl port just to isolate the shader problems in it besides what SDL2 does. Now it's a little more difficult as dhewm3 evolved but could be easier than an Amiga Warpos version :)