gluTessBeginPolygon()

NAME

gluTessBeginPolygon − delimit a polygon description

SYNOPSIS

void gluTessBeginPolygon(
GLUtesselator∗ tess,
GLvoid∗ data );

PARAMETERS

tessSpecifies the tessellation object (created with gluNewTess()).

dataSpecifies a pointer to user polygon data.

DESCRIPTION

gluTessBeginPolygon() 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.

EXAMPLE

A quadrilateral with a triangular hole in it can be described as follows:

gluTessBeginPolygon(tobj, NULL);
gluTessBeginContour(tobj);
    gluTessVertex(tobj, v1, v1);
    gluTessVertex(tobj, v2, v2);
    gluTessVertex(tobj, v3, v3);
    gluTessVertex(tobj, v4, v4);
gluTessEndContour(tobj);
gluTessBeginContour(tobj);
    gluTessVertex(tobj, v5, v5);
    gluTessVertex(tobj, v6, v6);
    gluTessVertex(tobj, v7, v7);
gluTessEndContour(tobj);
gluTessEndPolygon(tobj);

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