gluBeginTrim man page on OpenBSD

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GLUBEGINTRIM(3G)					      GLUBEGINTRIM(3G)

NAME
       gluBeginTrim, gluEndTrim - delimit a NURBS trimming loop definition

C SPECIFICATION
       void gluBeginTrim( GLUnurbs* nurb )

       void gluEndTrim( GLUnurbs* nurb )

       delim $$

PARAMETERS
       nurb   Specifies the NURBS object (created with gluNewNurbsRenderer).

DESCRIPTION
       Use gluBeginTrim to mark the beginning of a trimming loop, and
       gluEndTrim to mark the end of a trimming loop. A trimming loop is a set
       of oriented curve segments (forming a closed curve) that define
       boundaries of a NURBS surface. You include these trimming loops in the
       definition of a NURBS surface, between calls to gluBeginSurface and
       gluEndSurface.

       The definition for a NURBS surface can contain many trimming loops. For
       example, if you wrote a definition for a NURBS surface that resembled a
       rectangle with a hole punched out, the definition would contain two
       trimming loops. One loop would define the outer edge of the rectangle;
       the other would define the hole punched out of the rectangle. The
       definitions of each of these trimming loops would be bracketed by a
       gluBeginTrim/gluEndTrim pair.

       The definition of a single closed trimming loop can consist of multiple
       curve segments, each described as a piecewise linear curve (see
       gluPwlCurve) or as a single NURBS curve (see gluNurbsCurve), or as a
       combination of both in any order. The only library calls that can
       appear in a trimming loop definition (between the calls to gluBeginTrim
       and gluEndTrim) are gluPwlCurve and gluNurbsCurve.

       The area of the NURBS surface that is displayed is the region in the
       domain to the left of the trimming curve as the curve parameter
       increases. Thus, the retained region of the NURBS surface is inside a
       counterclockwise trimming loop and outside a clockwise trimming loop.
       For the rectangle mentioned earlier, the trimming loop for the outer
       edge of the rectangle runs counterclockwise, while the trimming loop
       for the punched-out hole runs clockwise.

       If you use more than one curve to define a single trimming loop, the
       curve segments must form a closed loop (that is, the endpoint of each
       curve must be the starting point of the next curve, and the endpoint of
       the final curve must be the starting point of the first curve). If the
       endpoints of the curve are sufficiently close together but not exactly
       coincident, they will be coerced to match.  If the endpoints are not
       sufficiently close, an error results (see gluNurbsCallback).

       If a trimming loop definition contains multiple curves, the direction
       of the curves must be consistent (that is, the inside must be to the
       left of all of the curves). Nested trimming loops are legal as long as
       the curve orientations alternate correctly.  If trimming curves are
       self-intersecting, or intersect one another, an error results.

       If no trimming information is given for a NURBS surface, the entire
       surface is drawn.

EXAMPLE
       This code fragment defines a trimming loop that consists of one
       piecewise linear curve, and two NURBS curves:

       gluBeginTrim(nobj);
	  gluPwlCurve(..., GLU_MAP1_TRIM_2);
	  gluNurbsCurve(..., GLU_MAP1_TRIM_2);
	  gluNurbsCurve(..., GLU_MAP1_TRIM_3); gluEndTrim(nobj);

SEE ALSO
       gluBeginSurface(3G), gluNewNurbsRenderer(3G), gluNurbsCallback(3G),
       gluNurbsCurve(3G), gluPwlCurve(3G)

								 March 1, 2011
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