pnon_uniform_b_spline_curve3(3g) — Subroutines

Name

pnon_uniform_b_spline_curve3 − Specifies the 3D nonuniform B-spline curve primitive.

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

Syntax

void pnon_uniform_b_spline_curve3 (
const Pcurve_geom_spline ∗geom_spline /∗ (I) Curve geometry
spline ∗/
)

Data Structures

typedef struct {
    Pint                order;         /∗ spline order ∗/
    Pfloat_list         knots;         /∗ list of knot values ∗/
    Pfloat              low_limit;     /∗ lower parameter range limit ∗/
    Pfloat              high_limit;    /∗ high parameter range limit ∗/
    Pctrl_point3_list   ctrl_points;   /∗ list of control points ∗/
} Pcurve_geom_spline;
    typedef struct {
        Pint     num_floats;    /∗ number of floats in the list ∗/
        Pfloat ∗floats;        /∗ list of floats ∗/
    } Pfloat_list;
    typedef struct {
        Prationality   rationality;   /∗ control point rationality ∗/
        Pint           num_points;    /∗ number of control points ∗/
        Ppoint3_ptr    points;        /∗ list of control points ∗/
    } Pctrl_point3_list;
        typedef enum {
            PB_SPLINE_RATIONAL,        /∗ rational (4D) points ∗/
            PB_SPLINE_NON_RATIONAL     /∗ nonrational (3D) points ∗/
        } Prationality;
        typedef union {
            Ppoint3       ∗point3;       /∗ pointer to 3D nonhomogeneous
                                            points ∗/
            Phomo_point4 ∗homo_point4; /∗ pointer to 4D homogeneous
                                            points ∗/
        } Ppoint3_ptr;
            typedef struct {
                Pfloat   x;   /∗ x coordinate ∗/
                Pfloat   y;   /∗ y coordinate ∗/
                Pfloat   z;   /∗ z coordinate ∗/
            } Ppoint3;
            typedef struct {
                Pfloat   wx;   /∗ wx coordinate ∗/
                Pfloat   wy;   /∗ wy coordinate ∗/
                Pfloat   wz;   /∗ wz coordinate ∗/
                Pfloat   w;    /∗ homogeneous coordinate ∗/
            } Phomo_point4;

Description

pnon_uniform_b_spline_curve3 specifies the three-dimensional nonuniform B-spline curve primitive, a primitive consisting of a curve determined by connecting points.

Depending on the 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 curve 3 element.

During structure traversal, the polyline set 3 with data primitive attributes provide additional data. Digital PHIGS computes the curve approximation criteria, and draws a nonuniform B-spline curve 3. The following are important considerations when using this function:

•The spline order must be a positive integer. The knots must form an increasing sequence of numbers.

•The type parameter may have the enumerated value PB_SPLINE_RATIONAL or PB_SPLINE_NON_RATIONAL. The number of control points must be at least as large as the spline order. The number of control points plus the spline order must equal the number of knots.

•The low_limit and high_limit fields specify over what range Digital PHIGS evaluates the B-spline curve. The field low_limit must be less than or equal to the high_limit value.

•At structure traversal, PHIGS draws a nonuniform B-spline curve primitive with the attributes used by polyline set 3 with data, and the current curve approximation criteria. It uses these for values ranging from low_limit to high_limit.

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

Museum

pnon_uniform_b_spline_curve3(3g) — Subroutines

Name

Syntax

Data Structures

Description

See Also