NURB Patches
A NURB patch is a surface defined by ratios of B-spline surfaces, which are three-dimensional analogs of B-spline curves. A NURB patch is defined by the TQ3NURBPatchData data type. See "Creating and Editing NURB Patches," beginning on page 4-166 for a description of the routines you can use to create and edit NURB patches. Figure 4-19 shows a NURB patch.
Figure 4-19 A NURB patch
typedef struct TQ3NURBPatchData {
unsigned long uOrder;
unsigned long vOrder;
unsigned long numRows;
unsigned long numColumns;
TQ3RationalPoint4D *controlPoints;
float *uKnots;
float *vKnots;
unsigned long numTrimLoops;
TQ3NURBPatchTrimLoopData *trimLoops;
TQ3AttributeSet patchAttributeSet;
} TQ3NURBPatchData;
Field Description
uOrder
- The order of the NURB patch in the u parametric direction. For NURB patches defined by ratios of B-spline polynomials that are cubic in u, the order is 4. In general, the order of a NURB patch defined by polynomial equations in which u is of degree n is n+1. The value in this field must be greater than 1.
vOrder
- The order of the NURB patch in the v parametric direction. For NURB patches defined by ratios of B-spline polynomials that are cubic in v, the order is 4. In general, the order of a NURB patch defined by polynomial equations in which v is of degree n is n+1. The value in this field must be greater than 1.
numRows
- The number of control points in the u parametric direction. The value of this field must be greater than 1.
numColumns
- The number of control points in the v parametric direction. The value of this field must be greater than 1.
controlPoints
- A pointer to an array of rational four-dimensional control points that define the NURB patch. The first control point in the array is the lower-left corner of the NURB patch. The control points are listed in a rectangular order, first in the direction of increasing u and then in the direction of increasing v. The number of elements in this array is the product of the values in the
numRows and numColumns fields.
uKnots
- A pointer to an array of knots in the u parametric direction that define the NURB curve. The number of u knots in a NURB curve is the sum of the values in the
uOrder and numRows fields. The values in this array must be nondecreasing (but successive values may be equal).
vKnots
- A pointer to an array of knots in the v parametric direction that define the NURB curve. The number of v knots in a NURB curve is the sum of the values in the
vOrder and numColumns fields. The values in this array must be nondecreasing (but successive values may be equal).
numTrimLoops
- The number of trim loops in the array pointed to by the
trimLoops field. Currently this field should contain the value 0.
trimLoops
- A pointer to an array of trim loop data structures that define the loops used to trim a NURB patch. See below for the structure of the trim loop data structure. Currently this field should contain the value
NULL.
patchAttributeSet
- A set of attributes for the NURB patch. The value in this field is
NULL if no NURB patch attributes are defined.
A trim loop data structure is defined by the TQ3NURBPatchTrimLoopData data type.
typedef struct TQ3NURBPatchTrimLoopData {
unsigned long numTrimCurves;
TQ3NURBPatchTrimCurveData *trimCurves;
} TQ3NURBPatchTrimLoopData;
Field Description
numTrimCurves
- The number of trim curves in the array pointed to by the
trimCurves field.
trimCurves
- A pointer to an array of trim curve data structures that define the curves used to trim a NURB patch. See below for the structure of the trim curve data structure.
A trim curve data structure is defined by the TQ3NURBPatchTrimCurveData data type.
typedef struct TQ3NURBPatchTrimCurveData {
unsigned long order;
unsigned long numPoints;
TQ3RationalPoint3D *controlPoints;
float *knots;
} TQ3NURBPatchTrimCurveData;
Field Description
order
- The order of the NURB trim curve. In general, the order of a NURB trim curve defined by polynomial equations of degree n is n+1. The value in this field must be greater than 1.
numPoints
- The number of control points that define the NURB trim curve. The value in this field must be greater than 2.
controlPoints
- A pointer to an array of three-dimensional rational control points that define the NURB trim curve.
knots
- A pointer to an array of knots that define the NURB trim curve. The number of knots in a NURB trim curve is the sum of the values in the
order and numPoints fields. The values in this array must be nondecreasing (but successive values may be equal).
