Add option to Lock Spline Points

[D.T. Nethery]

Here is a request for improving the Spline Tools such as B-Spline : please make it possible to LOCK points on the spline , similar to how points in the Warp tool grid can be locked by clicking the point and holding down Shift. So if I create a spline that curves in one direction , then click to make a new point starting in a different direction the new point will not distort the previous points. (because those previous points will be locked in place) Does that make sense ?

See the screen captures. I've created a line with the B-Spline tool , formed with four points. BUT if I click to make a fifth point after the fourth point it distorts the line and I have to re-adjust the previous points to pull the line back to how I had it , then continue on adding points . I would like to have it so the previous points can be locked (or maybe it only needs to be the fourth point that is locked ?) , so when I make the next point the previous line will not be distorted.

[Thierry]

We'll look into this, at first sight it seems doable.

[D.T. Nethery]

Thanks ! I hope it will work.

[Svengali]

I don't quite understand what is being requested here... isn't the fundamental nature of spline curves that they are a sum of the control points that define them? And the power of spline curves is that each point can be individually adjusted to modify the local segment of the curve relative to that point's two immediate neighbors, and to a lesser extent, the two segments beyond those two points... all other segments of the derived curve remain stable and unchanged.

As it now works, once the spline's points are established, in effect they remain LOCKED until any individual point is explicitly re-positioned and the curve segment effected by that point is modified accordingly.

What am I missing?
sven

[D.T. Nethery]

As shown in the screen shot above. Let's imagine I've set a line with three or four spline points , that line is exactly where I want it , I don't want that line to move , but now I want to continue adding more points after the last point to add to the line . If I add a new point it messes up the position of the line which must now be readjusted to get it back to where it was before. If the previous points could be locked (similar to how the points on the Warp tool are locked) the new point(s) added after the locked point will not cause the line to be shift out of place.

[Svengali]

David, Here is a link to an explanation of T Splines, intended for new Rhino software users, but I think the first couple of minutes nicely explain the interaction of control points and how they influence the resultant curve.

IMO I don't think it is possible to make spline-building that will work like you want (i.e. locking some points).

There are two distinct stages in interactive spline design.
Stage one: Interactive design of the spline by ADDING OR MOVING POINTS to customize the curve. The complex spline is really a visualization of a mathematical formula based on the positions of all the control points. So, all the points must be available for repositioning.
Stage two: After the spline is the way you want it, you APPLY the spline and the final line is drawn.

Reworking the Spline.
In TVPaint you can re-activate the last spline, modify the control points and reapply the spline: First press UNDO which will erase the last generated line. Then press ENTER and the previous spline and control points reappear so they can be further manipulated.

As mentioned in the video, you can better control short segments of the spline by adding control points close around where the curve misbehaves. You might try something like that.

OR, maybe Thierry or one of the other TVPaint programmers can add something to the spline design process that will be a workable solution for you.

sven