MirBSD manpage: gluTessNormal(3)



     gluTessNormal - specify a normal for a polygon


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


     tess    Specifies the tessellation object (created with

     valueX  Specifies the first component of the normal.

     valueY  Specifies the second component of the normal.

     valueZ  Specifies the third component of the normal.


     gluTessNormal describes a normal for a polygon that the pro-
     gram 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 con-
     nected. It is expected that the input data lies approxi-
     mately 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.


     gluTessBeginPolygon(3G), gluTessEndPolygon(3G)

MirBSD #10-current     Printed 2021-12-07                       1

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