graPHIGS Programming Interface: Subroutine Reference

The graPHIGS Programming Interface : Subroutine Reference

GPTNBS - Trimmed Non-Uniform B-Spline Surface

GPTNBS (uorder, vorder, unum, vnum, uknots, vknots, tflag, utess, vtess, cflags, cwidth, ctlpts, ncontour, ncurve, curveinfo, tknot, ttess, cdwidth, cddata)

Purpose

Use GPTNBS to insert a Trimmed Non-Uniform B-Spline Surface structure element into the open structure following the element pointer or to replace the element pointed at by the element pointer with a Trimmed Non-Uniform B-Spline Surface structure element depending on the current edit mode.

At structure traversal time, a non-uniform parametric surface of the specified uorder and vorder are generated using the specified control points. Only the region of the surface which is bounded by an odd number of trimming curves is rendered.

This primitive generates no output if any of the following are true:

The requested orders for the basis functions of the surface or trimming curves are not supported by the workstation.

No trimming curves are specified.

The trimming curves must adhere to the following rules; otherwise, the results are unpredictable:

Each loop must be explicitly closed.

Curves cannot go outside the parameter range of the surface.

The trimming curves within a loop must be connected in a head to tail fashion. They may not be randomly specified. The end of one curve must coincide with the beginning of the next curve.

The trimming curves may not cross other trimming curves in the same or different loop.

The trimming curves have the following optional capability:

A mix of rational and non-rational curves can be used on the same surface.

The trimming curves can form multiple closed loops.

Each curve is parameterized independently.

Polygon and surface attributes are applied to this primitive.

GPTNBS is identified as GDP 1036.

Note:

Not all GDPs are supported on all workstations. Use the Inquire List of Generalized Drawing Primitives (GPQGD) subroutine to determine the GDPs supported by an opened workstation. See also the workstation description in The graPHIGS Programming Interface: Technical Reference

Parameters

uorder -- specified by user, fullword integer

Order of the basis functions for the u parameter (>=2)

vorder -- specified by user, fullword integer

Order of the basis functions for the v parameter (>=2)

unum -- specified by user, fullword integer

Number of surface control points for the u direction (>=uorder)

vnum -- specified by user, fullword integer

Number of surface control points for the v direction (>=vorder)

uknots -- specified by user, array of short floating-point numbers

Knot values for the u parameter. The length of this array must be uorder+ unum This parameter must be a non-decreasing knot value sequence.

vknots -- specified by user, array of short floating-point numbers

Knot values for the v parameter. The length of this array must be vorder+ vnum This parameter must be a non-decreasing knot value sequence.

tflag -- specified by user, fullword integer

Surface tessellation quality value flag. This parameter shows whether the tessellation quality values are specified or not.

Not specified.

Specified.

utess -- specified by user, array of short floating-point numbers

Tessellation quality values for the u direction. When the tflag parameter is set to a value of one, this parameter must contain unum- uorder+1 quality values. These values are used in conjunction with Surface Approximation Criteria method 8 to control the number of sub-divisions made in the u direction. The number of sub-divisions that are performed for a patch is approximately the product of this value and the Surface Approximation Criteria control value (u) in the traversal state list.

vtess -- specified by user, array of short floating-point numbers

Tessellation quality values for the v direction. When the tflag parameter is set to a value of one, this parameter must contain vnum- vorder+1 quality values. These values are used in conjunction with Surface Approximation Criteria method 8 to control the number of sub-divisions made in the v direction. The number of sub-divisions that are performed for a patch is approximately the product of this value and the Surface Approximation Criteria control value (v) in the traversal state list.

cflags -- specified by user, fullword integer

Control point optional data flags. This parameter shows what data is specified for each control point. The value specified should be the sum of the following values based on the fields that are specified in the ctlpts parameter.

Value

Meaning

Control point coordinates.

Weights are specified with each control point. This produces the rational form of the Non-Uniform B-Spline Surface.

cwidth -- specified by user, fullword integer

Number of words between subsequent entries of control points array ctlpts

ctlpts -- specified by user, array of short floating-point numbers.

Grid of control points. The control points are stored by row where a row is considered to be the direction associated with the u parameter. For example, the set of control points

                 ^
                 | m   n   o   p
                 |
                 | i   j   k   l
   Increasing v  |
                 | e   f   g   h
                 |
                 | a   b   c   d
                 --------------->
                    Increasing u

would be stored in the order a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, and p. The cwidth parameter must be at least three. If cflags specifies that weights are included with each control point, the cwidth parameter must be at least four. Each weight W must be greater than zero when specified.

Note: When W is specified, the control points are not in homogeneous form (i.e.,XW, YW, ZW, W) They are specified after division by W or (X, Y, Z, W)

ncontour -- specified by user, fullword integer

Number of contours to be generated (>=0)

ncurve -- specified by user, array of fullword integers

Number of curves in each contour. Each entry must be greater than or equal to one. The length of this array is defined by the value of the ncontour parameter.

curveinfo -- specified by user, array of curve data

Array containing information about each curve. Each entry of this parameter must have the following fields in this order:

Type of Curve -- fullword integer

This field must contain

3 -

Non-Uniform B-Spline curve

Options -- fullword integer

This parameter specifies various options of the curve. Each option is specified by a bit in this word and the following bits are currently defined.

Bit

Meaning

0-28

Reserved. Must be set to zero.

Tessellation quality flag.

If set, a tessellation quality value for each span of this curve is specified in the ttess parameter.

Weight flag.

If set, the curve is rational and the weight is specified for each control point in the cddata parameter.

Boundary flag.

If set, the curve is treated as an edge of the composite fill area.

Order -- fullword integer

Order of the curve (>=2)

Number of Data -- fullword integer

Number of entries of the cddata parameter used to define the curve. This parameter corresponds to the npoint parameter of the Non-Uniform B-Spline Curve 2. The specified number's entries of the cddata parameter are used as its ctlpts parameter.

Start -- short floating-point number

The parameter value representing the start point of the curve.

End -- short floating-point number

The parameter value representing the end point of the curve.

tknot -- specified by user, array of short floating-point numbers

Array of knot values for the t direction of the curve. The sequence of each list in this array is assumed to match the order of the curve definitions in curveinfo The length of each list equals the order + number of data for the curve.

ttess -- specified by user, array of short floating-point numbers

Array of tessellation quality values. This array must contain one list for each Non-Uniform B-Spline curve with a tessellation quality flag set to a value of one (specified). For other curves, this array is not referenced. The sequence of each list in this array is assumed to match the order of the curve definitions in curveinfo The length of each list equals the number of data - order + 1 of the curve.

cdwidth -- specified by user, fullword integer.

Specifies the number of fullwords between each entry of the array in cddata If there is any rational curve in the curveinfo parameter, this parameter must be at least three. Otherwise, it must be larger than or equal to two.

cddata -- specified by user, array of short floating-point numbers

This array must contain one list for each curve. The sequence of each list in this array is assumed to match the order of the curve definitions in curveinfo The length of each list equals the number of data field specified in the curveinfo parameter.

For each entry, the following fields are defined and the fields must be specified in this order without any gap.

U, V components --

2 short floating-point numbers

weight --

short floating-point number

Error Codes

5: FUNCTION REQUIRES STATE STOP OR NROP (NOT STCL)
341: ORDER OF BASIS FUNCTION < TWO
342: ORDER IS GREATER THAN NUMBER OF CONTROL POINTS
343: KNOT VECTOR IS INVALID
345: WEIGHT IN CONTROL POINT IS <= ZERO
347: PARAMETER LIMITS ARE OUTSIDE VALID PARAMETER RANGE
348: MINIMUM PARAMETER LIMIT > MAXIMUM
351: OPTIONAL DATA AVAILABILITY FLAG IS INVALID
353: NUMBER OF CONTOURS < ZERO
354: NUMBER OF CURVES PER CONTOUR < ONE
361: CURVE OPTIONS FIELD IS INVALID
362: TESSELLATION CONTROL VALUE IS INVALID
557: WIDTH PARAMETER < MINIMUM ALLOWED

Related Subroutines

GPBICD: Set Back Interior Color Direct
GPBICI: Set Back Interior Color Index
GPBSCD: Set Back Specular Color Direct
GPBSCI: Set Back Specular Color Index
GPBSPR: Set Back Surface Properties
GPECD: Set Edge Color Direct
GPECI: Set Edge Color Index
GPEI: Set Edge Index
GPELT: Set Edge Linetype
GPESC: Set Edge Scale Factor
GPFDMO: Set Face Distinguish Mode
GPICD: Set Interior Color Direct
GPICI: Set Interior Color Index
GPII: Set Interior Index
GPIS: Set Interior Style
GPISI: Set Interior Style Index
GPLMO: Set Lighting Calculation Mode
GPLSS: Set Light Source State
GPPGC: Set Polygon Culling
GPQTDF: Inquire Trimming Curve Display Facilities
GPSAC: Set Surface Approximation Criteria
GPSCD: Set Specular Color Direct
GPSCI: Set Specular Color Index
GPSPR: Set Surface Properties
GPTCAC: Set Trimming Curve Approximation Criteria

RCP code

201345027 (X'0C004803')