PBSS3D(3g) — Subroutines

Name

PBSS3D − Specifies the 3D form of the nonuniform B-spline surface with data primitive.

Operating States: PHOP, ∗, STOP, ∗
PHIGS PLUS function
Creates a structure element

Syntax

PBSS3D (USORD, VSORD, UNKA, VNKA, UKNOTS, VKNOTS, RTYPE, UNCP,
VNCP, PXA, PYA, PZA, PWA, TCLDR, TCREC, CSSLDR, CSSREC, DSSLDR, DSSREC)

Argument      Data Type      Access    Description
---------------------------------------------------------------------------
USORD         Integer        Read      U spline order
VSORD         Integer        Read      V spline order
UNKA          Integer        Read      Number of knots for U
VNKA          Integer        Read      Number of knots for V
UKNOTS(UNKA) Array of       Read      U knots
              reals
VKNOTS(VNKA) Array of       Read      V knots
              reals
RTYPE         Integer        Read      Rationality
UNCP          Integer        Read      U number of the control points
                                       dimension
VNCP          Integer        Read      V number of the control points
                                       dimension
PXA(UNCP ∗    Real           Read      Control points, in modeling
VNCP)                                  coordinates
PYA(UNCP ∗
VNCP)
PZA(UNCP ∗
VNCP)
PWA(UNCP ∗
VNCP)
TCLDR         Integer        Read      Number of array elements used in
                                       TCREC
TCREC(TCLDR) Character ∗80 Read      Trimming curve data record
CSSLDR        Integer        Read      Number of array elements used in
                                       CSSREC
CSSREC        Character ∗80 Read      Data record for the color spline
(CSSLDR)                               surface
DSSLDR        Integer        Read      Number of array elements used in
                                       DSSREC
DSSREC        Character ∗80 Read      Data record for the data spline
(DSSLDR)                               surface
--------------------------------------------------------------------------

Constants

Defined Argument     Constant     Description
---------------------------------------------------------------------------
RTYPE                PRAT         Rational (4D) control points
                     PNRAT        Nonrational (3D) control points
--------------------------------------------------------------------------

Description

PBSS3D specifies the three-dimensional form of the nonuniform B-spline surface with data primitive. It determines the surface area attributes of the nonuniform B-spline curve. For example, it might determine the color of the nonuniform B-spline surface.

Depending on the current edit mode, this function either inserts the new structure element directly after the element indicated by the pointer or replaces the element indicated by the pointer. The pointer then points to the new nonuniform B-spline surface 3 with data element.

During structure traversal, the fill area set 3 primitive attributes provide additional data. Digital PHIGS computes the curve approximation criteria and draws a nonuniform B-spline surface. This function fully specifies the three-dimensional nonuniform B-spline surface primitive. The surface U and V orders must be positive integers. The U knots and the V knots must each form an increasing sequence of numbers. Note the following considerations when using this function:

•The type parameter may have the enumerated value PRAT or PNRAT. When PRAT is specified, the control points must be specified as homogeneous modeling coordinates. For a PNRAT type, the control points are ordinary PHIGS modeling coordinates.

•The control points in the U and V directions must be at least as large as the corresponding order. If not, Digital PHIGS generates a spline of order equal to the number of control points in the corresponding direction. The number of control points in each direction plus the corresponding spline order must equal the corresponding number of knots. Excess knot values or control points are ignored.

•At structure traversal, PHIGS draws a nonuniform B-spline surface primitive with the attributes used by PFAS3D, and the current curve approximation criteria.

•Trimming curves define the surface parameter area to render. Digital PHIGS renders the rectangular parameter limits of the surface as the edges of the surface, based on the edge flag attribute when you have not specified any trimming curves.

•The trimming definition of a surface consists of a list of loops. Each of these loops is a list of one or more trimming curves, each of which is a nonuniform rational B-spline curve defined in the two-dimensional parameter space of the surface. The curves of a loop connect in a head-to-tail fashion. Each loop must be explicitly closed. If there is floating point inaccuracy in closure of trimming loops or head-to-tail connectivity between trimming curves, the implementation assumes closure or connectivity.

•Each trimming curve has a visibility flag that controls its visibility. When the edge flag attribute is off, trimming curves are not rendered as edges, though they may still be rendered where the interior style is HOLLOW.

If Digital PHIGS is in immediate mode, it performs this function immediately, but the function does not create a structure element.

Digital PHIGS Version 3.1 does not support this function.

See PPTC and PUTC for a description of the trimming curve data record. See PPCSS and PUCSS for a description of the color spline surface data record. See PPDSS and PUDSS for a description of the data spline surface data record.

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PBSS3D(3g) — Subroutines

Name

Syntax

Constants

Description

See Also