nurbss(3G)nurbss(3G)NAMEnurbss - controls the shape of a NURBS surface
FORTRAN 77 SPECIFICATION
subroutine nurbss(sknotcount, s_knot, tknotcount, t_knot,
+ soffset, toffset, ctlarray, sorder, torder, type)
integer*4 sknotcount, tknotcount
double precision sknot(sknotcount), tknot(tknotcount)
integer*4 soffset, toffset
double precision ctlarray(*)
integer*4 sorder, torder, type
PARAMETERS
sknotcount expects the number of knots in the parametric s direction.
sknot expects an array of sknotcount non-decreasing knot values
in the parametric s direction.
tknotcount expects the number of knots in the parametric t direction.
tknot expects an array of tknotcount non-decreasing knot values
in the parametric t direction.
soffset expects the offset (in bytes) between successive control
points in the parametric s direction in ctlarray.
toffset expects the offset (in bytes) between successive control
points in the parametric t direction in ctlarray.
ctlarray expects an array containing control points for the NURBS
surface. The coordinates must appear as either (x, y, z)
triples or as (wx, wy, wz, w) quadruples. The offsets
between successive control points in the parametric s and
t directions are given by soffset and toffset.
sorder expects the order of the NURBS surface in the parametric s
direction. The order is one more than the degree, hence,
a cubic surface has an order of 4.
torder expects the order of the NURBS surface in the parametric t
direction. The order is one more than the degree, hence,
a cubic surface has an order of 4.
type expects a value indicating the control point type.
Current options are NV3D, NV3DR, NC4D, NC4DR, and NT2D,
NT2DR. Types NV3D and NV3DR denote double-precision
positional coordinates in a three-dimensional model space.
NV3D denotes non-rational (3) coordinates and NV3DR
denotes rational (4) coordinates. Types NC4D and NC4DR
denote double-precision color coordinates in a four-
dimensional RGBA color space. NC4D denotes non-rational
coordinates and NC4DR denotes rational coordinates. Types
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nurbss(3G)nurbss(3G)
NT2D and NT2DR denote double-precision texture coordinates
in a two-dimensional texture space. NT2D denotes non-
rational coordinates and NT2DR denotes rational
coordinates.
DESCRIPTION
Use the nurbss command within a NURBS (Non-Uniform Rational B-Spline)
surface definition to describe the shape of a NURBS surface before any
trimming takes place. To mark the beginning of a NURBS surface
definition, use the bgnsur command. To mark the end of a NURBS surface
definition, use the endsur command. Call nurbss within a NURBS surface
definition only.
Positional, texture, and color coordinates are associated by presenting
each as a separate nurbss between a bgnsur/endsurf pair. No more than
one call to nurbss for each of color and texture data may be made within
a single bgnsur/endsurf pair. Exactly one call must be made to describe
position data and it must be the last call to nurbss between the
bracketing bgnsur/endsurf.
EXAMPLE
call bgnsur
call nurbss( ..., N_C4D )
call nurbss( ..., N_T2D )
call nurbss( ..., N_V3D )
call endsur
You can trim a NURBS surface by using the commands nurbsc and pwlcur
between calls to bgntri and endtri.
Observe that a nurbss with sknotcount knots in the s direction and
tknotcount knots in the t direction with orders sorder and torder must
have (sknotcount - sorder) x (tknotcount - torder) control points.
The system renders a NURBS surface as a polygonal mesh and analytically
calculates normal vectors at the corners of the polygons within the mesh.
Therefore, your code should specify a lighting model when it uses NURBS
surfaces. Otherwise, you loose all the interesting surface information.
Use lmdef and lmbind to define or modify materials and their properties.
See the Graphics Library Programming Guide for a mathematical description
of a NURBS surface.
SEE ALSO
bgnsur, nurbsc, bgntri, pwlcur, setnur, getnur, texbin
NOTEnurbss commands specifying color or texture coordinates currently have no
effect on IRIS-4D G, GT, GTX, and Personal IRIS.
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