gluNextContour - mark the beginning of another contour
void gluNextContour( GLUtriangulatorObj *tobj, GLenum type )
tobj Specifies the tessellation object (created with gluNewTess). type Specifies the type of the contour being defined. Valid values are GLU_EXTERIOR, GLU_INTERIOR, GLU_UNKNOWN, GLU_CCW, and GLU_CW.
gluNextContour is used in describing polygons with multiple contours. After the first contour has been described through a series of gluTessVertex calls, a gluNextContour call indicates that the previous contour is complete and that the next contour is about to begin. Another series of gluTessVertex calls is then used to describe the new contour. This process can be repeated until all contours have been described. type defines what type of contour follows. The legal contour types are as follows: GLU_EXTERIOR An exterior contour defines an exterior boundary of the polygon. GLU_INTERIOR An interior contour defines an interior boundary of the polygon (such as a hole). GLU_UNKNOWN An unknown contour is analyzed by the library to determine if it is interior or exterior. GLU_CCW, GLU_CW The first GLU_CCW or GLU_CW contour defined is considered to be exterior. All other contours are considered to be exterior if they are oriented in the same direction (clockwise or counterclockwise) as the first contour, and interior if they are not. If one contour is of type GLU_CCW or GLU_CW, then all contours must be of the same type (if they are not, then all GLU_CCW and GLU_CW contours will be changed to GLU_UNKNOWN). Note that there is no real difference between the GLU_CCW and GLU_CW contour types. gluNextContour can be called before the first contour is described to define the type of the first contour. If gluNextContour is not called before the first contour, then the first contour is marked GLU_EXTERIOR.
A quadrilateral with a triangular hole in it can be described as follows:
gluBeginPolygon(tobj);
gluTessVertex(tobj, v1, v1);
gluTessVertex(tobj, v2, v2);
gluTessVertex(tobj, v3, v3);
gluTessVertex(tobj, v4, v4);
gluNextContour(tobj, GLU_INTERIOR);
gluTessVertex(tobj, v5, v5);
gluTessVertex(tobj, v6, v6);
gluTessVertex(tobj, v7, v7);
gluEndPolygon(tobj);
gluBeginPolygon, gluNewTess, gluTessCallback, gluTessVertex
Introduction | Alphabetic | Specification
Last Edited: Fri, May 26, 1995