Create tangent lines between two curves.

Input parameters:

1. Ca → First curve for tangent lines.
2. Cb → Second curve for tangent lines.
3. Ma → Tangency constraint along the first curve.
   • 0 → Any
   • 1 → Along
   • 2 → Against
   • 3 → Clear
4. Mb → Tangency constraint along the second curve.
   • 0 → Any
   • 1 → Along
   • 2 → Against
   • 3 → Clear

Output parameters:

1. Ln → Lines connecting the first and second curves.
2. La → Loci at line start points on the first curve.
3. Lb → Loci at line end points on the second curve.
4. Xd → Cumulative tangent angle error, as measured between the line and both curves at the points of coincidence.