gluTessProperty

GLUTESSPROPERTY(3G)					  GLUTESSPROPERTY(3G)



NAME
       gluTessProperty - set a tessellation object property


C SPECIFICATION
       void gluTessProperty( GLUtesselator* tess,
			     GLenum which,
			     GLdouble data )


PARAMETERS
       tess   Specifies the tessellation object (created with gluNewTess).

       which  Specifies	  the	property   to	be   set.  Valid  values  are
	      GLU_TESS_WINDING_RULE,		      GLU_TESS_BOUNDARY_ONLY,
	      GLU_TESS_TOLERANCE.

       data   Specifies the value of the indicated property.

DESCRIPTION
       gluTessProperty is used to control properties stored in a tessellation
       object. These properties affect the way that the polygons  are  inter-
       preted and rendered.  The legal values for which are as follows:

       GLU_TESS_WINDING_RULE
		      Determines which parts of the polygon are on the "inte-
		      rior".  data may be set to one of GLU_TESS_WINDING_ODD,
		      GLU_TESS_WINDING_NONZERO, GLU_TESS_WINDING_POSITIVE, or
		      GLU_TESS_WINDING_NEGATIVE,			   or
		      GLU_TESS_WINDING_ABS_GEQ_TWO.

		      To understand how the winding rule works, consider that
		      the input contours partition the	plane  into  regions.
		      The  winding rule determines which of these regions are
		      inside the polygon.

		      For a single contour C, the winding number of a point x
		      is  simply  the  signed  number  of revolutions we make
		      around x as we travel once around C (where CCW is posi-
		      tive).  When there are several contours, the individual
		      winding numbers are summed. This procedure associates a
		      signed  integer  value  with each point x in the plane.
		      Note that the winding number is the same for all points
		      in a single region.



















		      The winding rule classifies a region as "inside" if its
		      winding number belongs to	 the  chosen  category	(odd,
		      nonzero,	positive,  negative,  or absolute value of at
		      least two). The previous GLU tessellator (prior to  GLU
		      1.2) used the "odd" rule. The "nonzero" rule is another
		      common way to define  the	 interior.  The	 other	three
		      rules are useful for polygon CSG operations.

       GLU_TESS_BOUNDARY_ONLY
		      Is a boolean value ("value" should be set to GL_TRUE or
		      GL_FALSE). When set to GL_TRUE, a set  of	 closed	 con-
		      tours  separating the polygon interior and exterior are
		      returned instead of a tessellation.  Exterior  contours
		      are  oriented  CCW with respect to the normal; interior
		      contours	are  oriented  CW.  The	 GLU_TESS_BEGIN	  and
		      GLU_TESS_BEGIN_DATA callbacks use the type GL_LINE_LOOP
		      for each contour.

       GLU_TESS_TOLERANCE
		      Specifies a tolerance for merging	 features  to  reduce
		      the size of the output.  For example, two vertices that
		      are very close to each other might  be  replaced	by  a
		      single  vertex.  The  tolerance  is  multiplied  by the
		      largest coordinate magnitude of any input vertex;	 this
		      specifies	 the  maximum  distance	 that any feature can
		      move as the result of a single merge  operation.	If  a
		      single  feature takes part in several merge operations,
		      the total distance moved could be larger.

		      Feature merging is completely optional;  the  tolerance
		      is only a hint.  The implementation is free to merge in
		      some cases and not in others, or to  never  merge	 fea-
		      tures at all. The initial tolerance is 0.

		      The current implementation merges vertices only if they
		      are exactly coincident, regardless of the current	 tol-
		      erance.  A  vertex  is spliced into an edge only if the
		      implementation is unable to distinguish which  side  of
		      the  edge the vertex lies on. Two edges are merged only
		      when both endpoints are identical.

SEE ALSO
       gluGetTessProperty(3G), gluNewTess(3G)



							  GLUTESSPROPERTY(3G)