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gluTessProperty - set a tessellation object property
gluTessProperty( GLUtesselator* tess,
GLdouble data )
eqn not supported
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:
- Specifies the tessellation object (created
- 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.
- 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,
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.
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.
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.
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