glutessnormal(3g) [centos man page]

GLUTESSNORMAL(3G)						   OpenGL Manual						 GLUTESSNORMAL(3G)

NAME

       gluTessNormal - specify a normal for a polygon

C SPECIFICATION

       void gluTessNormal(GLUtesselator* tess, GLdouble valueX, GLdouble valueY, GLdouble valueZ);

PARAMETERS

       tess
	   Specifies the tessellation object (created with gluNewTess()).

       valueX
	   Specifies the first component of the normal.

       valueY
	   Specifies the second component of the normal.

       valueZ
	   Specifies the third component of the normal.

DESCRIPTION

       gluTessNormal describes a normal for a polygon that the program is defining. All input data will be projected onto a plane perpendicular to
       one of the three coordinate axes before tessellation and all output triangles will be oriented CCW with respect to the normal (CW
       orientation can be obtained by reversing the sign of the supplied normal). For example, if you know that all polygons lie in the x-y plane,
       call gluTessNormal(tess, 0.0, 0.0, 1.0) before rendering any polygons.

       If the supplied normal is (0.0, 0.0, 0.0) (the initial value), the normal is determined as follows. The direction of the normal, up to its
       sign, is found by fitting a plane to the vertices, without regard to how the vertices are connected. It is expected that the input data
       lies approximately in the plane; otherwise, projection perpendicular to one of the three coordinate axes may substantially change the
       geometry. The sign of the normal is chosen so that the sum of the signed areas of all input contours is nonnegative (where a CCW contour
       has positive area).

       The supplied normal persists until it is changed by another call to gluTessNormal.

SEE ALSO

       gluTessBeginPolygon(), gluTessEndPolygon()

COPYRIGHT

       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS

       opengl.org

opengl.org							    06/10/2014							 GLUTESSNORMAL(3G)

GLUTESSVERTEX(3G)						   OpenGL Manual						 GLUTESSVERTEX(3G)

NAME

       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 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).

EXAMPLE

       A quadrilateral with a triangular hole in it can be described as follows:

	   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);

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 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 when the data 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).

SEE ALSO

       gluNewTess(), gluTessBeginContour(), gluTessBeginPolygon(), gluTessCallback(), gluTessEndPolygon(), gluTessNormal(), gluTessProperty()

COPYRIGHT

       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS

       opengl.org

opengl.org							    06/10/2014							 GLUTESSVERTEX(3G)