Edit: as the 3mb PDF was too large for the post, I've shared it here as JPGs instead. So whenever you read "first page of the PDF", etc., in the OP, just translate that to "first image attached below", etc., which attached images can be seen below, in order.
I was figuring-out for myself how a screen's x- and y-coordinates are mutated in order to produce the illusion of a 3D-shape in 3D-graphic-design.
The first page of the attached PDF shows how I went about this, and I'll here explain it further. So, if we imagine a rectangular screen centrally...