The Math Behind Perspective in .ass Subtitles
I'll be honest, I completely forgot about this page and only rediscovered it now when going through all my old ramblings so I could link them on this blog. I don't think anything in there is wrong, but it's fairly outdated at this point. (It was written after I got Zahuczky's old Perspective-Motion script to work correctly, but before I built Aegisub's built-in perspective tool or my own improved PerspectiveMotion script.) Still, I'll link it here for completeness.
If you're interested in the math behind the new perspective tools, I tried my best to structure and comment the code of both Aegisub's built-in perspective tool and my Perspective.moon module used in the perspective scripts as well as possible, so you should hopefully be able to read those for more insights.
Link: https://github.com/TypesettingTools/arch1t3cht-Aegisub-Scripts/blob/main/doc/perspective_math.md