_C_ License Applicability. Except to the extent portions of this file are _C_ made subject to an alternative license as permitted in the SGI Free _C_ Software License B, Version 1.1 (the "License"), the contents of this _C_ file are subject only to the provisions of the License. You may not use _C_ this file except in compliance with the License. You may obtain a copy _C_ of the License at Silicon Graphics, Inc., attn: Legal Services, 1600 _C_ Amphitheatre Parkway, Mountain View, CA 94043-1351, or at: _C_ _C_ http://oss.sgi.com/projects/FreeB _C_ _C_ Note that, as provided in the License, the Software is distributed on an _C_ "AS IS" basis, with ALL EXPRESS AND IMPLIED WARRANTIES AND CONDITIONS _C_ DISCLAIMED, INCLUDING, WITHOUT LIMITATION, ANY IMPLIED WARRANTIES AND _C_ CONDITIONS OF MERCHANTABILITY, SATISFACTORY QUALITY, FITNESS FOR A _C_ PARTICULAR PURPOSE, AND NON-INFRINGEMENT. _C_ _C_ Original Code. The Original Code is: OpenGL Sample Implementation, _C_ Version 1.2.1, released January 26, 2000, developed by Silicon Graphics, _C_ Inc. The Original Code is Copyright (c) 1991-2000 Silicon Graphics, Inc. _C_ Copyright in any portions created by third parties is as indicated _C_ elsewhere herein. All Rights Reserved. _C_ _C_ Additional Notice Provisions: The application programming interfaces _C_ established by SGI in conjunction with the Original Code are The _C_ OpenGL(R) Graphics System: A Specification (Version 1.2.1), released _C_ April 1, 1999; The OpenGL(R) Graphics System Utility Library (Version _C_ 1.3), released November 4, 1998; and OpenGL(R) Graphics with the X _C_ Window System(R) (Version 1.3), released October 19, 1998. This software _C_ was created using the OpenGL(R) version 1.2.1 Sample Implementation _C_ published by SGI, but has not been independently verified as being _C_ compliant with the OpenGL(R) version 1.2.1 Specification. _C_ _C_ $Date: 2004/03/14 08:29:09 $ $Revision: 1.1.1.4 $ _C_ The first character in this file must be an '_'! _C_ Anything on a line after _C_ is ignored _define(_filters,eqn)_C_ _C_ eqn is automatically replaced with neqn for nroff _header(TessVertex, specify a vertex on a polygon) _names(TessVertex) .EQ delim $$ .EN .SH PARAMETERS _phead(_param1) Specifies the tessellation object (created with _cmnd(NewTess)). _phead(_param2) Specifies the location of the vertex. _phead(_param3) Specifies an opaque pointer passed back to the program with the vertex callback (as specified by _cmnd(TessCallback)). .SH DESCRIPTION _cmnd describes a vertex on a polygon that the program defines. Successive _cmnd calls describe a closed contour. For example, to describe a quadrilateral _cmnd should be called four times. _cmnd can only be called between _cmnd(TessBeginContour) and _cmnd(TessEndContour). .P _param3 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 _gluconst(TESS_VERTEX) or _gluconst(TESS_VERTEX_DATA) callback after tessellation (see the _cmnd(TessCallback) reference page). .SH EXAMPLE A quadrilateral with a triangular hole in it can be described as follows: .sp .Ex gluTessBeginPolygon(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); .Ee .sp .SH NOTES It is a common error to use a local variable for _param2 or _param3 and store values into it as part of a loop. For example: .Ex 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); } .Ee .P This doesn't work. Because the pointers specified by _param2 and _param3 might not be dereferenced until _cmnd(TessEndPolygon) is executed, all the vertex coordinates but the very last set could be overwritten before tessellation begins. .P Two common symptoms of this problem are consists of a single point (when a local variable is used for _param3) and a _gluconst(TESS_NEED_COMBINE_CALLBACK) error (when a local variable is used for _param2). .SH SEE ALSO _cmnd(TessBeginPolygon), _cmnd(NewTess), _cmnd(TessBeginContour), _cmnd(TessCallback), _cmnd(TessProperty), _cmnd(TessNormal), _cmnd(TessEndPolygon)