three 基础库
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( function () {
/**
* NURBS curve object
*
* Derives from THREE.Curve, overriding getPoint and getTangent.
*
* Implementation is based on (x, y [, z=0 [, w=1]]) control points with w=weight.
*
**/
class NURBSCurve extends THREE.Curve {
constructor( degree, knots
/* array of reals */
, controlPoints
/* array of Vector(2|3|4) */
, startKnot
/* index in knots */
, endKnot
/* index in knots */
) {
super();
this.degree = degree;
this.knots = knots;
this.controlPoints = []; // Used by periodic NURBS to remove hidden spans
this.startKnot = startKnot || 0;
this.endKnot = endKnot || this.knots.length - 1;
for ( let i = 0; i < controlPoints.length; ++ i ) {
// ensure THREE.Vector4 for control points
const point = controlPoints[ i ];
this.controlPoints[ i ] = new THREE.Vector4( point.x, point.y, point.z, point.w );
}
}
getPoint( t, optionalTarget = new THREE.Vector3() ) {
const point = optionalTarget;
const u = this.knots[ this.startKnot ] + t * ( this.knots[ this.endKnot ] - this.knots[ this.startKnot ] ); // linear mapping t->u
// following results in (wx, wy, wz, w) homogeneous point
const hpoint = THREE.NURBSUtils.calcBSplinePoint( this.degree, this.knots, this.controlPoints, u );
if ( hpoint.w !== 1.0 ) {
// project to 3D space: (wx, wy, wz, w) -> (x, y, z, 1)
hpoint.divideScalar( hpoint.w );
}
return point.set( hpoint.x, hpoint.y, hpoint.z );
}
getTangent( t, optionalTarget = new THREE.Vector3() ) {
const tangent = optionalTarget;
const u = this.knots[ 0 ] + t * ( this.knots[ this.knots.length - 1 ] - this.knots[ 0 ] );
const ders = THREE.NURBSUtils.calcNURBSDerivatives( this.degree, this.knots, this.controlPoints, u, 1 );
tangent.copy( ders[ 1 ] ).normalize();
return tangent;
}
}
THREE.NURBSCurve = NURBSCurve;
} )();