It's a WndProc, feel free to split each message into a separate function but that's not actually helping anyones understanding.

Ehh it doesn't seem to be a problem. Understanding the function doesn't require thinking about those 900 lines at once since the code for handling each message type doesn't interact with any other code in the function.

I am very proud of the code base, but there's many places to optimize. I welcome contributions if you want to help out!