/vr/ - Retro Games

So how the fuck do skyboxes work? DSDA, software mode.

The red ridge is in the center of the 256px wide texture. The linedef I am looking at is 128 px wide.
Now I am wondering how that picture is generated. If the texture were drawn at the start of the sidedef, I wouldn't get two ridges left and right.
Changing the length of the line doesn't do anything, so where the actual fuck does this thing start drawing the texture?
I would like to have that red ridge in the center.