Unreal Engine 1 software render technolgy? how it renders?

i am very very want a part of source code (or deep explanation) where Unreal uses software rendering system, how it do something like biliner (GL_LINEAR) texture filtering in software mode?
it will greatly be helpful for software rendered old open sourced games, which don’t want to use opengl or d3d.
speaking in details its for doom1,2 =) more details -> for zdaemon, odamex.
Please =)