gluTessProperty() gluTessProperty()
gluTessProperty - set a tessellation object property
void gluTessProperty(
GLUtesselator* tess,
GLenum which,
GLdouble data );
Specifies the tessellation object (created with gluNewTess()).
Specifies the property to be set. Valid values
are GLU_TESS_WINDING_RULE, GLU_TESS_BOUNDARY_ONLY,
GLU_TESS_TOLERANCE. Specifies the value of the indicated
property.
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: 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, 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. 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. 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.
gluGetTessProperty(3)
gluTessProperty()
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