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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)

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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)
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