I noticed that people relatively often ask for a way to draw an inverted circle and don't have an easy way to implement it, since it requires a bit of math that can be difficult to derive without experience. I decided to make a quick cart and standalone function to do that! This isn't amazingly efficient, and it only does circles (not ellipses), but it is a drop in function:
Update: new function utilizing trig, faster and now subpixel!
Old versions: