Source: math/NURBSCurve.js

import {Point} from './Point';
import {Curve} from './Curve';
import {NURBSUtils} from './NURBSUtils';

/**
 *
 * @class
 * @memberof JC
 * @param {Number} degree
 * @param {Array}  knots           array of reals
 * @param {Array}  controlPoints   array of Point
 */
function NURBSCurve( degree, knots, controlPoints ) {
  this.degree = degree;
  this.knots = knots;
  this.controlPoints = controlPoints; // [];
}


NURBSCurve.prototype = Object.create( Curve.prototype );
NURBSCurve.prototype.constructor = NURBSCurve;


NURBSCurve.prototype.getPoint = function( t ) {
  let u = this.knots[0] + t * (
    this.knots[this.knots.length - 1] -
    this.knots[0]
  ); // linear mapping t->u

  // following results in (wx, wy, wz, w) homogeneous point
  let hpoint = 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 new Point( hpoint.x, hpoint.y, hpoint.z );
};


NURBSCurve.prototype.getTangent = function( t ) {
  let u = this.knots[0] + t * (
    this.knots[this.knots.length - 1] -
    this.knots[0]
  );
  let ders = NURBSUtils.calcNURBSDerivatives(
    this.degree,
    this.knots,
    this.controlPoints,
    u,
    1
  );
  let tangent = ders[1].clone();
  tangent.normalize();

  return tangent;
};

export {NURBSCurve};