[torginus]

That would only be true if a row (by which I mean a scanline) would be equidistant in view-space depth across its whole length, which is not quite true. While a column of pixels for a wall is (as long as you dont tilt the camera).

[tadfisher]

The code exists! https://github.com/id-Software/DOOM/blob/master/linuxdoom-1....

And it looks to me like we are mapping each row with a constant y, calculating the "distance" (thus scale factor) only once using just the vertical slope for the row.

[torginus]

Yeah sorry, you are right - I got it mixed up.

[Jare]

For the record, there were constant-Z full 3D engines in the late 90s, which would find the correct axes on screen to render perspective-correct textured triangles using oblique spans of pixels. They were incredibly complicated and prone to holes at the slightest numerical accuracy, but they were a sight to behold. Constant-Z meant not just saving on perspective divides, but also easy Z-buffer and depth-based fog.