1GLUTESSVERTEX(3G)                                            GLUTESSVERTEX(3G)
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NAME

6       gluTessVertex - specify a vertex on a polygon
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C SPECIFICATION

10       void gluTessVertex( GLUtesselator* tess,
11                           GLdouble *location,
12                           GLvoid* data )
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PARAMETERS

16       tess      Specifies the tessellation object (created with gluNewTess).
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18       location  Specifies the location of the vertex.
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20       data      Specifies  an  opaque pointer passed back to the program with
21                 the vertex callback (as specified by gluTessCallback).
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DESCRIPTION

24       gluTessVertex describes a vertex on a polygon that the program defines.
25       Successive  gluTessVertex calls describe a closed contour. For example,
26       to describe a quadrilateral gluTessVertex should be called four  times.
27       gluTessVertex  can  only  be  called  between  gluTessBeginContour  and
28       gluTessEndContour.
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30       data normally points to a structure containing the vertex location,  as
31       well  as  other  per-vertex  attributes such as color and normal.  This
32       pointer is passed back to  the  user  through  the  GLU_TESS_VERTEX  or
33       GLU_TESS_VERTEX_DATA    callback    after    tessellation    (see   the
34       gluTessCallback reference page).
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EXAMPLE

37       A quadrilateral with a triangular hole in it can be described  as  fol‐
38       lows:
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40       gluTessBeginPolygon(tobj, NULL);
41        gluTessBeginContour(tobj);
42          gluTessVertex(tobj, v1, v1);
43          gluTessVertex(tobj, v2, v2);
44          gluTessVertex(tobj, v3, v3);
45          gluTessVertex(tobj, v4, v4);
46        gluTessEndContour(tobj);
47        gluTessBeginContour(tobj);
48          gluTessVertex(tobj, v5, v5);
49          gluTessVertex(tobj, v6, v6);
50          gluTessVertex(tobj, v7, v7);
51        gluTessEndContour(tobj); gluTessEndPolygon(tobj);
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NOTES

55       It  is  a common error to use a local variable for location or data and
56       store values into it as part of a loop.  For example: for (i = 0;  i  <
57       NVERTICES; ++i) {
58         GLdouble data[3];
59         data[0] = vertex[i][0];
60         data[1] = vertex[i][1];
61         data[2] = vertex[i][2];
62         gluTessVertex(tobj, data, data);
63         }
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65       This doesn't work.  Because the pointers specified by location and data
66       might not be dereferenced until gluTessEndPolygon is executed, all  the
67       vertex  coordinates  but  the very last set could be overwritten before
68       tessellation begins.
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70       Two common symptoms of this problem are  consists  of  a  single  point
71       (when    a    local    variable    is    used    for    data)   and   a
72       GLU_TESS_NEED_COMBINE_CALLBACK error (when a local variable is used for
73       location).
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SEE ALSO

76       gluTessBeginPolygon(3G),    gluNewTess(3G),    gluTessBeginContour(3G),
77       gluTessCallback(3G),      gluTessProperty(3G),       gluTessNormal(3G),
78       gluTessEndPolygon(3G)
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84                                                             GLUTESSVERTEX(3G)
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