gluTessProperty: set a tessellation object property.
C Specification |
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
- Specifies the tessellation object (created with gluNewTess).
- Specifies the property to be set. Valid values are
- Specifies the value of the indicated property.
- Determines which parts of the polygon are on the "interior".
data may be set to one of
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
- 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