bytev-charts/lib/plugin/three.js/examples/js/curves/NURBSCurve.js

基于echarts和JavaScript及ES6封装的一个可以直接调用的图表组件库，内置主题设计，简单快捷，且支持用户自定义配置； npm 安装方式: npm install bytev-charts 若启动提示还需额外install插件,则运行 npm install @babel/runtime-corejs2 即可;

import _Object$create from "@babel/runtime-corejs2/core-js/object/create";
console.warn("THREE.NURBSCurve: As part of the transition to ES6 Modules, the files in 'examples/js' were deprecated in May 2020 (r117) and will be deleted in December 2020 (r124). You can find more information about developing using ES6 Modules in https://threejs.org/docs/#manual/en/introduction/Installation.");
/**
 * NURBS curve object
 *
 * Derives from Curve, overriding getPoint and getTangent.
 *
 * Implementation is based on (x, y [, z=0 [, w=1]]) control points with w=weight.
 *
 **/

THREE.NURBSCurve = function (degree, knots
/* array of reals */
, controlPoints
/* array of Vector(2|3|4) */
, startKnot
/* index in knots */
, endKnot
/* index in knots */
) {
  THREE.Curve.call(this);
  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 (var i = 0; i < controlPoints.length; ++i) {
    // ensure Vector4 for control points
    var point = controlPoints[i];
    this.controlPoints[i] = new THREE.Vector4(point.x, point.y, point.z, point.w);
  }
};

THREE.NURBSCurve.prototype = _Object$create(THREE.Curve.prototype);
THREE.NURBSCurve.prototype.constructor = THREE.NURBSCurve;

THREE.NURBSCurve.prototype.getPoint = function (t, optionalTarget) {
  var point = optionalTarget || new THREE.Vector3();
  var 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

  var 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);
};

THREE.NURBSCurve.prototype.getTangent = function (t, optionalTarget) {
  var tangent = optionalTarget || new THREE.Vector3();
  var u = this.knots[0] + t * (this.knots[this.knots.length - 1] - this.knots[0]);
  var ders = THREE.NURBSUtils.calcNURBSDerivatives(this.degree, this.knots, this.controlPoints, u, 1);
  tangent.copy(ders[1]).normalize();
  return tangent;
};