Polymost

Polymost is a software and OpenGL renderer developed by Ken Silverman as a replacement for the Build engine. From December 2004 to February 2005, Randy worked on adding the software rendering parts of Polymost to ZDoom. After remaining a decade in unfinished form, it was removed in 2014 (^bbc3b69), so ZDoom 2.7.1 is the last released version of ZDoom containing this feature. GZDoom 3.0 added a new software-based 3-point renderer (without the Y-shearing when looking up and down), SoftPoly.

Wireframe mode.

Solid colors mode.

The Polymost renderer in ZDoom could only render world geometry, either in wireframe or in solid colors. It could be tested by setting r_polymost to 1 (wireframe), 2 (solid colors with wireframe) or 3 (solid colors without wireframe) in the console.

Note that:

1. It was overlaid on the software renderer output. In wireframe mode, it was still playable; but in solid colors mode, the polygons masked the normal view entirely, rendering actors invisible.
2. Since it was part of the software renderer, if you use the OpenGL renderer from GZDoom or Skulltag, this would have had no effect.

The two screenshots illustrate the difference between Doom's horizontal projection and the true 3D perspective of polymost.

Global tilt angle.

One other console variable affected the polymost rendering: gtang. It corresponded to the global tilt angle, in radians. Positive values tilted the angle clockwise, negative values tilted it counter-clockwise. With an approximation of π (positive or negative), the projection was upside-down.