HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 420

T gluTessVertex gluTessVertex gluTessVertex: specify a vertex on a polygon. C Specification void gluTessVertex( GLUtesselator* tess, GLdouble *location, GLvoid* data) Parameters tess location data Specifies the tessellation object (created with gluNewTess). Specifies the location of the vertex. Specifies an opaque pointer passed 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. 420 Chapter 18