Hi Burr, yeah that uses what is called a constraint-based curve modification system, to modify the control points in such a way to change the point that the curve is going through at one spot on it.

In MoI it's basically a mechanism for manipulating a few nearby control points all in one drag operation rather than dragging on points one at a time.

It is theoretically possible for this constraint mechanism to flag certain control points as non-movable, but aside from some kind of UI mechanism to control that (which is significant itself), adding in more constraints like that means more "force" will get applied to the control points that can move. Additional force like that tends to cause stuff like bulges or wiggles happening in the curve instead of a more natural deformation.

> and they showed a technique of actually showing "2 sets"
> of points in edit points mode.. One as is now in MoI and
> another set of points on curve (Maybe these could be the
> definable entity?)

Yeah, but having a whole set of constrained edit points located all on the curve really tends to cause wiggles when you edit them.

See here for a previous example of how those kinds of bulges happen in over constrained type editing:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3364.6

It tends to be really frustrating to use an editing system that introduces a lot of bulgy or wiggly areas into the curve that is being edited.

- Michael