Implementation We'll typically end up with a ton of points to draw for the spectrum, and some simplification is worthwhile; use the Ramer–Douglas–Peucker algorithm to reduce to a smaller number of points.

We'll modify the inbound polygon in place, such that anything we want to keep is at the start of the polygon and anything we want to omit is at the end, returning an iterator to the new end, i.e., the point one past the last point we want to keep.

Our goal here is to avoid reallocations. Since we're at worst going to be leaving this the same size, we should be able to work with what we have already.

Note that this is a functor; it's serially reusable, but not reentrant. Call it from one thread only. In practical use, that's not expected to be a problem, and it allows us to reuse allocated memory in a serial manner, rather than requesting it and freeing it constantly.