Hi NightCabbage,

> I think I understand it, but I'm still not sure why you
> couldn't change the trimming curves, except for the one
> problem of if you tried to move then outside the surface.

Well, you can't re-shape the surface by changing the trimming curves, which would probably be normally what you would expect to do by editing them like you would in a polygon modeling program.

For example, when you edit edges in a polygon program, it is not unusual to move the edge up or down in 3D or stuff like that to mush the points all around.

It would be theoretically possible to edit the trimming curves but it would not behave like the polygon modeling editing, it would be more like you would drag the curves around within the surface but not be able to move them up or down off the surface or stuff like that.

In the future at some point it would be good to try and enable that kind of special trim curve editing, but it will take quite a bit of work since there are all kinds of situations to look out for, like you can't make trim curves cross over one another or have outer loops cross over inner loops, deal with other edges and loops that are joined with that one, etc... etc...

- Michael