We want some way to store the control point sequence that lets us easily associate points with their renderable and hit-testable representations, since we need to alter all of these together as points get moved or added. We use FOrderedPoints for this, until we decide on how we want to store sequences of points in general. FOrderedPoints maintains a sequence of point ID's, the positions associated with each ID, and a mapping back from ID to position. The ID's can then be used to match to renderable points, hit-testable points, and segments going to the next point. A sequence of 3-component vectors that can be used to represent a polyline in 3d space, or some other sequence of control points in 3d space.