Looking at the document, it seems like Godot is calculating angles clockwise instead of anti-clockwise like what I thought was the standard method. Did I miss something or is it really backwards from most other software?

An excellent question that afaik has no good answer. It is just a convention.

I hate the term 'handedness', because it doesn't really fit human anatomy (at least not mine), but this is colloquially called a right handed coordinate system. This may have historical reasons because OpenGL uses a right handed coordinate system, and may change with Godot 4 because Vulkan uses a (guess) left handed coordinate system 😐️

Oof, really didn't want to hear that >_<

Here's hoping that upgrading to 4.0 will automatically handle the conversions. Thanks for the confirmation though

Well, coming from OpenGL, I have to rewire some synapses and rewrite parts of my algebra stuff ...

This is because games use the y-axis as facing down (for historical reasons leading back to CRT displays, which I explained in another thread). Since the y-axis is down, while in high school math the y-axis is up, this reverses things. For example, if you take sin(90) the result is 1. And since positive y is down in Godot for 2D (and the vast majority of games historically) then it makes sense that the line would point straight down. This is also how it is in HTML/CSS and WebGL, and a bunch of older 2D game engines. It's not a made up thing just for Godot.

It would also be good to not assume everything you learned in high school is correct. Some things are standard, some things are not, and some things are arbitrary and no answer is more correct than another. So if you see something unexpected, just keep reading and adjusting, don't be attached to what you think is the "right way" because many times there is no "right way" or the issue is more complex than you understand.