Digital Equipment Corporation OpenGL man pages

gluTessNormal.3gl (GLU version 1.2 and later)


  gluTessNormal	- specify a normal for a polygon

C Specification

  void gluTessNormal( GLUtesselator *tess,
		      GLdouble x,
		      GLdouble y,
		      GLdouble z )


  tess	Specifies the tessellation object (created with	gluNewTess).

  x	Specifies the first component of the normal.

  y	Specifies the second component of the normal.

  z	Specifies the third component of the normal.


  gluTessNormal	describes a normal for a polygon that the user 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) (the default 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 non-negative (where a CCW	contour	has positive area).

  The supplied normal persists until it	is changed by another call to

See Also

  gluTessBeginPolygon, gluTessEndPolygon

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Last Edited: Fri Dec 6 11:18:03 EST 1996 by AFV
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