gluTessNormal(3G)	       OpenGL Reference		     gluTessNormal(3G)

NAME    [Toc]    [Back]

     gluTessNormal - specify a normal for a polygon

C SPECIFICATION    [Toc]    [Back]

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

PARAMETERS    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

     gluTessBeginPolygon, gluTessEndPolygon


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