I wasn't going to change a bunch of stuff in the shader. It's cgwg's, after all. But I probably should have handled vertical games correctly at least.
If cgwg wants to do more work on it, that wold be great. I guess that if he doesn't want to, I can fix it up a bit so it can be included in MAME.
I can try to copy the format/style of MooglyGuy's shaders and I suppose I can figure out how to do a diff or a pull request if nobody else will.
It would take a few days or a week since I'm pretty busy work though.