Umm... yeah, forgot to say, I'm also known as SMG M7 or SMG in some places. And yes, those 3D floors are entirely walkable. There are also values for transparency, (good) swimmable water, and a "fog" render around them. I've been modding for GZdoom for about a year, since it came out.
What the problem was, though, was that the light renderer isn't too great, and you can't use software mode in any level that has a 3D floor, since Graf Zahl hasn't done anything for the normal renderer. I just noticed that SRB2 is both an OGL and software game, so I was wondering how that was accomplished. I've never used Legacy, and therefore didn't know about the code for lighting. Mostly just ignorance on my part. Too bad I can't code, or I'd put the option to play in software rendering.