GlVIS

glVIS is a builder for, developed by Jānis Legzdiņš, as a companion software for glBSP. The GL_PVS lumps it creates serve a purpose similar in a way to that of the REJECT lump, allowing the engines which use it to know which subsectors can be skipped by the renderer entirely. Vavoom, ZDoomGL (v1), and Strife: Veteran Edition are known to make use of GL_PVS lumps.