Страницы справочника OS X

Эта страница руководства является частью версии 5.0 Инструментов XCode

Читать страницы руководства

GLUBEGINTRIM(3G)                                                                            GLUBEGINTRIM(3G)



NAME
       gluBeginTrim, gluEndTrim - delimit a NURBS trimming loop definition


C SPECIFICATION
       void gluBeginTrim( GLUnurbs* nurb )

       void gluEndTrim( GLUnurbs* nurb )


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 trim-ming trimming
       ming 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 defi-nition definition
       nition  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  trim-ming trimming
       ming 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 trim-ming trimming
       ming 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  consis-tent consistent
       tent  (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)






                                                                                            GLUBEGINTRIM(3G)