Specifies a vertex on a polygon.
OpenGL C bindings library: libGL.a
void gluTessVertex(GLUtesselator* tess, GLdouble *location, GLvoid* data)
The gluTessVertex subroutine describes a vertex on a polygon that the user is defining. Successive gluTessVertex calls describe a closed contour. For example, to describe a quadrilateral, the gluTessVertex subroutine must be called four times.
This subroutine can only be called between gluBeginContour and gluEndContour.
The data parameter normally points to a structure containing the vertex location, as well as other vertex-specific attributes (such as color and normal). This pointer is passed back to the user through the GLU_TESS_VERTEX or GLU_TESS_VERTEX_DATA callback after tessellation. (See the gluTessCallback subroutine for details on defining callbacks for a tessellation object.)
| /usr/include/GL/gl.h | Contains C language constraints, variable type definitions, and ANSI function prototypes for OpenGL. |
A quadrilateral with a triangle hole in it can be described as follows:
gluBeginPolygon(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);
It is a common error to use a local variable for location or
data and store values into it as part of a loop.
For example: for (i = 0; i < NVERTICES; ++i) {
GLdouble data[3];
data[0] = vertex[i][0];
data[1] = vertex[i][1];
data[2] = vertex[i][2];
gluTessVertex(tobj, data, data);
}
This doesn't work. Because the pointers specified by location and data might not be dereferenced until gluTessEndPolygon is executed, all the vertex coordinates but the very last set could be overwritten before tessellation begins.
Two common symptoms of this problem are consists of a single point (when a local variable is used for data) and a GLU_TESS_NEED_COMBINE_CALLBACK error (when a local variable is used for location.
The gluBeginPolygon subroutine, gluNewTess subroutine, gluTessBeginContour subroutine, gluTessCallback subroutine, gluTessProperty subroutine, gluTessNormal subroutine, gluTessEndPolygon subroutine.