100 lines
3.7 KiB
Plaintext
100 lines
3.7 KiB
Plaintext
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'\" e
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'\"! eqn | mmdoc
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'\"macro stdmacro
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.ds Vn Version 1.2
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.ds Dt 6 March 1997
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.ds Re Release 1.2.0
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.ds Dp May 02 11:53
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.ds Dm 37 tessprope
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.ds Xs 36693 6 tessproperty.gl
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.TH GLUTESSPROPERTY 3G
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.SH NAME
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.B "gluTessProperty
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\- set a tessellation object property
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.SH C SPECIFICATION
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void \f3gluTessProperty\fP(
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GLUtesselator* \fItess\fP,
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.nf
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.ta \w'\f3void \fPgluTessProperty( 'u
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GLenum \fIwhich\fP,
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GLdouble \fIdata\fP )
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.fi
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.EQ
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delim $$
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.EN
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.SH PARAMETERS
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.TP \w'\fIwhich\fP\ \ 'u
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\f2tess\fP
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Specifies the tessellation object (created with \%\f3gluNewTess\fP).
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.TP
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\f2which\fP
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Specifies the property to be set. Valid values are
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\%\f3GLU_TESS_WINDING_RULE\fP,
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\%\f3GLU_TESS_BOUNDARY_ONLY\fP,
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\%\f3GLU_TESS_TOLERANCE\fP.
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.TP
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\f2data\fP
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Specifies the value of the indicated property.
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.SH DESCRIPTION
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\%\f3gluTessProperty\fP is used to control properties stored in a tessellation object. These
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properties affect the way that the polygons are interpreted and rendered.
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The legal values for \f2which\fP are as follows:
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.TP 15
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\%\f3GLU_TESS_WINDING_RULE\fP
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Determines which parts of the polygon are on the "interior".
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\f2data\fP may be set to one of \%\f3GLU_TESS_WINDING_ODD\fP,
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\%\f3GLU_TESS_WINDING_NONZERO\fP, \%\f3GLU_TESS_WINDING_POSITIVE\fP, or
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\%\f3GLU_TESS_WINDING_NEGATIVE\fP, or \%\f3GLU_TESS_WINDING_ABS_GEQ_TWO\fP.
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.IP
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To understand how the winding rule works, consider that the input
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contours partition the plane into regions. The winding rule determines which
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of these regions are inside the polygon.
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.IP
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For a single contour C, the winding number of a point x is simply the signed
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number of revolutions we make around x as we travel once around C
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(where CCW is positive). When there are several contours, the individual
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winding numbers are summed. This procedure associates a signed integer
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value with each point x in the plane. Note that the winding number is the
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same for all points in a single region.
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.bp
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.IP
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The winding rule classifies a region as "inside" if its winding number
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belongs to the chosen category (odd, nonzero, positive, negative, or
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absolute value of at least two). The previous GLU tessellator (prior to
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GLU 1.2) used the "odd" rule. The "nonzero" rule is another common way to
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define the interior. The other three rules are useful for polygon CSG
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operations.
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.TP
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\%\f3GLU_TESS_BOUNDARY_ONLY\fP
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Is a boolean value ("value" should be set
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to GL_TRUE or GL_FALSE). When set to GL_TRUE, a set of closed contours
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separating the polygon interior and exterior are returned instead of a
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tessellation. Exterior contours are oriented CCW with respect to the
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normal; interior contours are oriented CW. The \%\f3GLU_TESS_BEGIN\fP
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and \%\f3GLU_TESS_BEGIN_DATA\fP callbacks use the type GL_LINE_LOOP for
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each contour.
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.TP
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\%\f3GLU_TESS_TOLERANCE\fP
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Specifies a tolerance for merging features to reduce the size of the output.
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For example, two vertices that are very close to each other might be
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replaced by a single vertex. The tolerance is multiplied by the largest
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coordinate magnitude of any input vertex; this specifies the maximum
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distance that any feature can move as the result of a single merge
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operation. If a single feature takes part in several merge operations, the
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total distance moved could be larger.
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.IP
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Feature merging is completely optional; the tolerance is only a hint.
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The implementation is free to merge in some cases and not in others, or to
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never merge features at all. The initial tolerance is 0.
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.IP
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The current implementation merges vertices only if they are exactly
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coincident, regardless of the current tolerance. A vertex is spliced into
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an edge only if the implementation is unable to distinguish which side of
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the edge the vertex lies on. Two edges are merged only when both endpoints
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are identical.
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.SH SEE ALSO
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\%\f3gluGetTessProperty(3G)\fP,
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\%\f3gluNewTess(3G)\fP
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