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gluTessProperty
Chapter 18
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gluTessProperty
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 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, 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 ruledetermines 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
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