Basics on Programming a Canvas for a CAD-System [pdf]

Good stuff- I had to learn most of this on my own.

Pro-tip: most of what you describe and document is already built into Qt, in the Graphics View Framework. It handles all the gunk around coordinate systems, canvas, zoom, scrollbars, and scaling, along with item groups, hit testing, multiple views of the same model, and extensive performance optimizations.

I have recently used Gemini to write an entire 2D CAD system based on this and it worked pretty well (I've already written one by hand).

Book "Basics on Programming a Canvas for a CAD-System - Coordinate Systems, Canvas, Zoom, Scrollbars, Drawing to Scale" by Mario Blunk