glutessproperty(3g) [xfree86 man page]

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  "interior".   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 positive). 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, posi-
		      tive, 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 contours 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 features at all. The initial tolerance is 0.

		      The current implementation merges vertices only if they are exactly coincident, regardless of the current tolerance. A  ver-
		      tex  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)

Check Out this Related Man Page

GLUNEXTCONTOUR(3G)														GLUNEXTCONTOUR(3G)

NAME

       gluNextContour - mark the beginning of another contour

C SPECIFICATION

       void gluNextContour( GLUtesselator* tess,
			    GLenum type )

PARAMETERS

       tess  Specifies the tessellation object (created with gluNewTess).

       type  Specifies the type of the contour being defined. Valid values are GLU_EXTERIOR, GLU_INTERIOR, GLU_UNKNOWN, GLU_CCW, and GLU_CW.

DESCRIPTION

       gluNextContour  is  used  in  describing  polygons  with  multiple contours. After the first contour has been described through a series of
       gluTessVertex calls, a gluNextContour call indicates that the previous contour is complete and that the next contour  is  about	to  begin.
       Another	series	of gluTessVertex calls is then used to describe the new contour. This process can be repeated until all contours have been
       described.

       type defines what type of contour follows.  The legal contour types are as follows:

       GLU_EXTERIOR	 An exterior contour defines an exterior boundary of the polygon.

       GLU_INTERIOR	 An interior contour defines an interior boundary of the polygon (such as a hole).

       GLU_UNKNOWN	 An unknown contour is analyzed by the library to determine if it is interior or exterior.

       GLU_CCW,

       GLU_CW		 The first GLU_CCW or GLU_CW contour defined is considered to be exterior. All other contours are considered to  be  exte-
			 rior  if  they  are  oriented in the same direction (clockwise or counterclockwise) as the first contour, and interior if
			 they are not.

       If one contour is of type GLU_CCW or GLU_CW, then all contours must be of the same type (if they are not, then all GLU_CCW and GLU_CW  con-
       tours will be changed to GLU_UNKNOWN).

       Note that there is no real difference between the GLU_CCW and GLU_CW contour types.

       Before  the  first  contour  is	described, gluNextContour can be called to define the type of the first contour.  If gluNextContour is not
       called before the first contour, then the first contour is marked GLU_EXTERIOR.

       This command is obsolete and is provided for backward compatibility only. Calls to gluNextContour are mapped to gluTessEndContour  followed
       by gluTessBeginContour.

EXAMPLE

       A quadrilateral with a triangular hole in it can be described as follows:

       gluBeginPolygon(tobj);
	  gluTessVertex(tobj, v1, v1);
	  gluTessVertex(tobj, v2, v2);
	  gluTessVertex(tobj, v3, v3);
	  gluTessVertex(tobj, v4, v4); gluNextContour(tobj, GLU_INTERIOR);
	  gluTessVertex(tobj, v5, v5);
	  gluTessVertex(tobj, v6, v6);
	  gluTessVertex(tobj, v7, v7); gluEndPolygon(tobj);

SEE ALSO

       gluBeginPolygon(3G), gluNewTess(3G), gluTessCallback(3G), gluTessVertex(3G), gluTessBeginContour(3G)

																GLUNEXTCONTOUR(3G)

Linux and UNIX Man Pages

glutessproperty(3g) [xfree86 man page]

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