Thanks to https://github.com/mancausoft I figured out that the whole wide aperture code I added yesterday wasn't correct - I replaced the logic used to thicken lines into rectangles which now works for circular and rectangular apertures (still making circular ones into rectangles though).

I also fixed a few bugs causing division by zero errors for circles with tiny areas and zero-length elements.

The main lesson here is to never use trigonometry for something that can be solved with vectors.