class TringTvor: public ZRCStone

 Returns old number of vertices.

 Returns old number of triangles.

 Calculates triangle normal from vertex-data and stores it into 'normal'.
 Returns original norm of the vector.

 This is to be used when triangle normals are not stored or during
 construction of the tvor.

 Calculates triangle normal from vertex-data and stores it into
 'normal'. Returns original norm of the vector. Center-of-gravity
 of the triangle is returned in 'cog'.

 This is to be used when triangle normals are not stored or during
 construction of the tvor.

 Assign random colors to different triangle strips.

 Generate per-vertex normals by averaging over normals of all triangles
 sharing the vertex.
 Requires building of intermediate structure.

 ??? Need an argument: weight normal contribution by triangle area
 ??? or ... perhaps better ... by vertex angle.
     This is somewhat done in vertex-connection stuff in Var1::TriMesh.

 Populate array of vectors 'trings_per_vert' from triangle data.
 The output array must be properly allocated in advance.

 Populate array of vectors 'neighbours' from triangle data.
 The output array must be properly allocated in advance.
 Returns total number of connections (which is 2*N_edge for closed
 surfaces).

 Exports triangle-data as POV mesh2 object.
 By experimentation I would say that smooth triangles do not work properly
 in pov-3.6.1 (15.10.2006).

 Find other two vertices (than v) in triangle t.
 If you do: e1 = v_prev - v, e2 = v_next - v, then: e2 x e1 points
 in the normal direction.

 Returns square distance from vertex vi to fiven point p.

 Returns square length of line between a and b.

 Stores min and max edge lengths into the passed refs.