gluNextContour — mark the beginning of another contour
void gluNextContour( | GLUtesselator* | tess, |
| GLenum | type); |
tessSpecifies 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_EXTERIORAn exterior contour defines an exterior boundary of the polygon.
GLU_INTERIORAn interior contour defines an interior boundary of the polygon (such as a hole).
GLU_UNKNOWNAn 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.
Before the first contour is described, gluNextContour can be called 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.
This command is obsolete and is provided for backward compatibility
only. Calls to gluNextContour are mapped to gluTessEndContour
followed by
gluTessBeginContour.
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);
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