gluTessProperty man page on RedHat
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GLUTESSPROPERTY(3G) OpenGL Manual 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, and
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
interpreted 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,
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, 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 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 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(), gluNewTess()
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org
opengl.org 03/16/2013 GLUTESSPROPERTY(3G)
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