luckily there's already a union algorithm that i'd forgotten that i wrote :)
notably, if either of the input paths is a different clockwise direction, then the union doesn't work as we'd intuitively think it would (since a reversed path would mean everything 'outside' the path is actually 'inside', etc)
both paths need to be clockwise, or both need to be counter-clockwise
luckily there's already a union algorithm that i'd forgotten that i wrote :)
notably, if either of the input paths is a different clockwise direction, then the union doesn't work as we'd intuitively think it would (since a reversed path would mean everything 'outside' the path is actually 'inside', etc)
both paths need to be clockwise, or both need to be counter-clockwise