# Triangulator¶

class Triangulator

This class can triangulate a convex or concave polygon, even one with holes. It is adapted from an algorithm published as:

Narkhede A. and Manocha D., Fast polygon triangulation algorithm based on Seidel’s Algorithm, UNC-CH, 1994.

http://www.cs.unc.edu/~dm/CODE/GEM/chapter.html

It works strictly on 2-d points. See Triangulator3 for 3-d points.

Inheritance diagram

Triangulator(void)
Triangulator(Triangulator const&) = default
void add_hole_vertex(int index)

Adds the next consecutive vertex of the current hole. This vertex should index into the vertex pool established by repeated calls to add_vertex().

The vertices may be listed in either clockwise or counterclockwise order. Vertices should not be repeated.

void add_polygon_vertex(int index)

Adds the next consecutive vertex of the polygon. This vertex should index into the vertex pool established by repeated calls to add_vertex().

The vertices may be listed in either clockwise or counterclockwise order. Vertices should not be repeated. In particular, do not repeat the first vertex at the end.

int add_vertex(LPoint2d const &point)
int add_vertex(double x, double y)

Adds a new vertex to the vertex pool. Returns the vertex index number.

void begin_hole(void)

Finishes the previous hole, if any, and prepares to add a new hole.

void clear(void)

Removes all vertices and polygon specifications from the Triangulator, and prepares it to start over.

void clear_polygon(void)

Removes the current polygon definition (and its set of holes), but does not clear the vertex pool.

int get_num_triangles(void) const

Returns the number of triangles generated by the previous call to triangulate().

int get_num_vertices(void) const

Returns the number of vertices in the pool. Note that the Triangulator might append new vertices, in addition to those added by the user, if any of the polygon is self-intersecting, or if any of the holes intersect some part of the polygon edges.

int get_triangle_v0(int n) const

Returns vertex 0 of the nth triangle generated by the previous call to triangulate().

This is a zero-based index into the vertices added by repeated calls to add_vertex().

int get_triangle_v1(int n) const

Returns vertex 1 of the nth triangle generated by the previous call to triangulate().

This is a zero-based index into the vertices added by repeated calls to add_vertex().

int get_triangle_v2(int n) const

Returns vertex 2 of the nth triangle generated by the previous call to triangulate().

This is a zero-based index into the vertices added by repeated calls to add_vertex().

LPoint2d const &get_vertex(int n) const

Returns the nth vertex.

bool is_left_winding(void) const

Returns true if the polygon vertices are listed in counterclockwise order, or false if they appear to be listed in clockwise order.

void triangulate(void)

Does the work of triangulating the specified polygon. After this call, you may retrieve the new triangles one at a time by iterating through get_triangle_v0/1/2().