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gluTessVertex

Chapter 18

420

gluTessVertex

gluTessVertex: specify a vertex on a polygon.

C Speciﬁcation

void gluTessVertex(

GLUtesselator* tess,

GLdouble *location,

GLvoid* data)

Parameters

tess Speciﬁes the tessellation object (created with gluNewTess).

location Speciﬁes the location of the vertex.

data Speciﬁes an opaque pointerpassed back to the program with the vertex

callback (as speciﬁed by gluTessCallback).

Description

gluTessVertex describes a vertex on a polygon that the program deﬁnes. Successive

gluTessVertex calls describe a closed contour. For example, to describe a quadrilateral

gluTessVertex should be called four times. gluTessVertex can only be called between

gluTessBeginContour and gluTessEndContour.

data normally points to a structure containing the vertex location, as well as other

per-vertex 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 reference page).

Notes

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

de-referenced until gluTessEndPolygon is executed, all the vertex coordinates but the

very last set could be overwritten before tessellation begins.

HP b2600 Reference Guide

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