Today I added an on-screen protractor for measuring angles in quiz questions. It can be toggled on and off from any question, and can be dragged around and rotated into position to overlay an image in order to measure an angle. This is the first of a few tools I wish to implement, others may include plotting graphs and drawing on diagrams.
I think the question tools built into Canvas are a little basic, and something like Khan's Perseus would be better - Khan/perseus · GitHub - perhaps as a feature option (for those wanting that extra flexibility).
I have attached my source files for anyone who might find this useful.