Control over boundary conditions on cubic splines.

[fryguybob]

(Imported from http://code.google.com/p/diagrams/issues/detail?id=66. Original issue from fryguy...@gmail.com on February 16, 2012, 01:36:31 PM UTC)

In some cases it would be nice to combine cubic splines with other shapes and retain some degree of smoothness. For instance, you might want a specific segment to be straight. Metapost, NURBS, and Spiro, all allow for building curves like this, but I think that cubic splines could also be formulated with boundary conditions much like how the join in a closed cubic spline is solved with a fully symmetric tri-diagonal matrix.

[bergey]

The metafont code in -contrib at least partially addresses this. It's allows making segments straight, or specifying tangent direction at either end. It still needs work to connect smoothly with the rest of diagrams.

[byorgey]

@fryguybob, did you have other ideas on what this might mean, which is not addressed by the metafont stuff? Maybe this is another one of those tickets that we should either close or make more specific.

[fryguybob]

I think my original opening of the issue was for a "nice thing to have" but I've never worked out what it would take in the particular cubic splines that we have. Metapost clearly has worked out the details so if that is working we should just close this.