GLUTESSBEGINPOLYGON - Online Linux Manual PageSection : 3G NAME"gluTessBeginPolygon − delimit a polygon description C SPECIFICATIONvoid gluTessBeginPolygon( GLUtesselator* tess, GLvoid* data)PARAMETERStessSpecifies the tessellation object (created with gluNewTess). dataSpecifies a pointer to user polygon data. DESCRIPTIONgluTessBeginPolygon and gluTessEndPolygon delimit the definition of a convex, concave or self-intersecting polygon. Within each gluTessBeginPolygon/gluTessEndPolygon pair, there must be one or more calls to gluTessBeginContour/gluTessEndContour. Within each contour, there are zero or more calls to gluTessVertex. The vertices specify a closed contour (the last vertex of each contour is automatically linked to the first). See the gluTessVertex, gluTessBeginContour, and gluTessEndContour reference pages for more details. data is a pointer to a user-defined data structure. If the appropriate callback(s) are specified (see gluTessCallback), then this pointer is returned to the callback function(s). Thus, it is a convenient way to store per-polygon information. Once gluTessEndPolygon is called, the polygon is tessellated, and the resulting triangles are described through callbacks. See gluTessCallback for descriptions of the callback functions. EXAMPLEA quadrilateral with a triangular hole in it can be described as follows: