All my work thus far on solving the drawflag/renderflag/additive/subtractive conundrum.
Outstandng problems:
* Bad additive/subtractive tables means that they appear opaque except under certain conditions.
* No support for FOFs, Polyobjects, or linedefs in OpenGL yet.
* All OpenGL support mostly done blind, may or may not function in practice.
If nothing else, the hard engineering problems are solved and it's just bug hammering...