Extract the wireframe curves of a surface.

Input parameters:

1. Sf → Surface for wireframe extraction.
2. Ds → Wireframe density. Values -2, -1, and 0 have special meaning, while positive integers determine the isocurve density.
   • -2 → Naked Edges
   • -1 → Creased Edges
   •  0 → Smooth Edges
   •  1 → Isocurves

Output parameters:

1. Wf → Complete wireframe containing all the curves implied by the given density.
2. En → All the naked edges in the wireframe.
3. Ec → All the sharp interior edges in the wireframe.
4. Et → All the smooth interior edges in the wireframe.
5. Cu → All isocurves in the u-direction in the wireframe.
6. Cv → All isocurves in the v-direction in the wireframe.