The toon shaders in XSI v1.x are direct ports from Softimage|3D without any optimizations. That is why some of their functions have been crippled (such as hiding inkline seams).
In XSI v2.0, the toon shaders were completely rewritten from scratch and contain many improvements over the old toon shaders. Including the ability to render true wireframe images showing surface tessellation with controls to hide edges of coplanar polygons.
If you have XSI v2.0, you can also compile the shader case study in the SDK example section. The tutorial covers how to write a simple wireframe texture shader. It will render faster than the toon shaders as it's applied as a texture, but the lines won't necessarily have uniform thickness because they aren't perspective corrected (eg: no compensation made for depth or viewing angle).
If you're using NURBS surfaces, you can use the "grid" shader to render the wireframes. Just set color1 to your desired wirecolor, and set color2 completely transparent.
Matt
Matt Lind
Animator / Technical Director
Softimage certified instructor:
Softimage|3D
Softimage|XSI
speye_21@hotmail.com