gluTessNormal

The gluTessNormal function specifies a normal for a polygon.

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

Parameters

tess

The tessellation object (created with gluNewTess).

x

The x-coordinate component of a normal.

y

The y-coordinate component of a normal.

z

The z-coordinate component of a normal.

Remarks

The gluTessNormal function describes a normal for a polygon that you define. All input data is projected onto a plane perpendicular to one of the three coordinate axes before tessellation, and all output triangles are oriented counterclockwise with respect to the normal. (To obtain clockwise orientation, reverse 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:

1. 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 can change the geometry substantially.
2. The sign of the normal is chosen so that the sum of the signed areas of all input contours is non-negative (where a counterclockwise contour has positive area).

The supplied normal persists until another call to gluTessNormal changes it.

QuickInfo

  Windows NT: Use version 3.5 and later.
  Windows: Use Windows 95 and later.
  Windows CE: Unsupported.
  Header: Declared in glu.h.
  Import Library: Link with glu32.lib.

See Also

gluNewTess, gluTessBeginPolygon, gluTessEndPolygon