3D Graphics Programming with QuickDraw 3D 1.5.4

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ASCII

NURBCurve2D

Binary

nb2c ( = 0x6E623263 )

Data Format

Uns32                               order
Uns32                               nPoints
RationalPoint3D                     points[nPoints]
Float32                             knots[order + nPoints]


order

The order of the NURB curve. In general, the order of a NURB curve defined by polynomial equations of degree n is n +1. The value of this field must be greater than 1.

nPoints

The number of control points that define the 2D NURB curve. The value of this field must be greater than 1.

points[]

An array of three-dimensional control points that define the 2D NURB curve. The z coordinate of each point in this array must be greater than 0.

knots[]

An array of knots that define the 2D NURB curve. The number of knots in a NURB curve is the sum of the values in the order and nPoints fields. The values in this array must be nondecreasing, but successive values may be equal.

Data Size

8 + 12 * nPoints + 4 * (order + nPoints)

Description

See "NURB Curves" for a general description of NURB curves. 2D NURB curves occur only as child objects to trim loop objects, and trim loop objects occur only as child objects to NURB patches. This object is the only two-dimensional curve permitted by 3D metafile Version 1.0.

Default Surface Parameterization

None.

Parent Hierarchy

Data.

Parent Objects

Trim loop object (always).

Child Objects

None.

Default Size

None.