3D Floors in software mode

I've noticed that in Legacy, there were only 3D Floors in OpenGL. How does SRB2 manage to render them in software mode without a z-buffer? I'm no programmer, but I'm trying to relay this to some other forums, so try to make it simple, please. :?

Legacy has 3D floors in software.

http://forum.drdteam.org/viewtopic.php?t=1016

Which confuses me about this...

It's talking about a different version of Doom. Also, SRB2 edits most of the code anyway.

"Legacy apparently has 3D floors in software mode. Couldn't that code be adopted into GZdoom? "

GZDoom appears to be pretty advanced. They even have sloped FOFs that are apparently walkable (Though I may be wrong).

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.