# al_triangulate_polygon man page

al_triangulate_polygon — Allegro 5 API

## Synopsis

`#include <allegro5/allegro_primitives.h> bool al_triangulate_polygon( const float* vertices, size_t vertex_stride, const int* vertex_counts, void (*emit_triangle)(int, int, int, void*), void* userdata)`

## Description

Divides a simple polygon into triangles, with zero or more other simple polygons subtracted from it - the holes. The holes cannot touch or intersect with the outline of the main polygon. Simple means the polygon does not have to be convex but must not be self-overlapping.

*Parameters:*

- ·
- vertices - Interleaved array of (x, y) vertex coordinates for each of the polygons, including holes.
- ·
- vertex_stride - distance (in bytes) between successive pairs of vertices in the array.
- ·
- vertex_counts - Number of vertices for each polygon. The number of vertices in the main polygon is given by vertex_counts[0] and must be at least three. Subsequent elements indicate the number of vertices in each hole. The array must be terminated with an element with value zero.
- ·
- emit_triangle - a function to be called for every set of three points that form a triangle. The function is passed the indices of the points in
`vertices`

and`userdata`

. - ·
- userdata - arbitrary data to be passed to emit_triangle.

## Since

5.1.0