100 lines
2.9 KiB
Plaintext
100 lines
2.9 KiB
Plaintext
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'\" e
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'\"! eqn | mmdoc
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'\"macro stdmacro
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.ds Vn Version 1.2
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.ds Dt 6 March 1997
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.ds Re Release 1.2.0
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.ds Dp May 02 11:53
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.ds Dm 37 tessverte
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.ds Xs 55990 5 tessvertex.gl
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.TH GLUTESSVERTEX 3G
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.SH NAME
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.B "gluTessVertex
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\- specify a vertex on a polygon
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.SH C SPECIFICATION
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void \f3gluTessVertex\fP(
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GLUtesselator* \fItess\fP,
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.nf
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.ta \w'\f3void \fPgluTessVertex( 'u
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GLdouble \fI*location\fP,
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GLvoid* \fIdata\fP )
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.fi
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.EQ
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delim $$
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.EN
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.SH PARAMETERS
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.TP \w'\fIlocation\fP\ \ 'u
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\f2tess\fP
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Specifies the tessellation object (created with \%\f3gluNewTess\fP).
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.TP
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\f2location\fP
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Specifies the location of the vertex.
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.TP
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\f2data\fP
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Specifies an opaque pointer passed back to the program with the vertex callback
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(as specified by \%\f3gluTessCallback\fP).
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.SH DESCRIPTION
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\%\f3gluTessVertex\fP describes a vertex on a polygon that the program defines. Successive
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\%\f3gluTessVertex\fP calls describe a closed contour. For example,
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to describe a quadrilateral \%\f3gluTessVertex\fP should be called four times.
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\%\f3gluTessVertex\fP can only be called between \%\f3gluTessBeginContour\fP and
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\%\f3gluTessEndContour\fP.
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.P
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\f2data\fP normally points to a structure containing the vertex
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location, as well as other per-vertex attributes such as color and normal.
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This pointer is passed back to the user through the \%\f3GLU_TESS_VERTEX\fP
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or \%\f3GLU_TESS_VERTEX_DATA\fP callback after tessellation
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(see the \%\f3gluTessCallback\fP reference page).
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.SH EXAMPLE
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A quadrilateral with a triangular hole in it can be described as follows:
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.sp
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.Ex
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gluTessBeginPolygon(tobj, NULL);
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gluTessBeginContour(tobj);
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gluTessVertex(tobj, v1, v1);
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gluTessVertex(tobj, v2, v2);
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gluTessVertex(tobj, v3, v3);
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gluTessVertex(tobj, v4, v4);
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gluTessEndContour(tobj);
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gluTessBeginContour(tobj);
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gluTessVertex(tobj, v5, v5);
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gluTessVertex(tobj, v6, v6);
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gluTessVertex(tobj, v7, v7);
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gluTessEndContour(tobj);
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gluTessEndPolygon(tobj);
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.Ee
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.sp
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.SH NOTES
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It is a common error to use a local variable for \f2location\fP or \f2data\fP and store
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values into it as part of a loop.
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For example:
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.Ex
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for (i = 0; i < NVERTICES; ++i) {
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GLdouble data[3];
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data[0] = vertex[i][0];
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data[1] = vertex[i][1];
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data[2] = vertex[i][2];
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gluTessVertex(tobj, data, data);
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}
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.Ee
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.P
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This doesn't work.
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Because the pointers specified by \f2location\fP and \f2data\fP might not be
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dereferenced until \%\f3gluTessEndPolygon\fP is executed,
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all the vertex coordinates but the very last set could be overwritten
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before tessellation begins.
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.P
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Two common symptoms of this problem are consists of a single point
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(when a local variable is used for \f2data\fP) and a
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\%\f3GLU_TESS_NEED_COMBINE_CALLBACK\fP error (when a local variable is
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used for \f2location\fP).
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.SH SEE ALSO
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\%\f3gluTessBeginPolygon(3G)\fP, \%\f3gluNewTess(3G)\fP, \%\f3gluTessBeginContour(3G)\fP,
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\%\f3gluTessCallback(3G)\fP,
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\%\f3gluTessProperty(3G)\fP, \%\f3gluTessNormal(3G)\fP,
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\%\f3gluTessEndPolygon(3G)\fP
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