@thi.ng/geom-splines/cubic-from-controlpoints.js

nD cubic & quadratic curve analysis, conversion, interpolation, splitting

import { add } from "@thi.ng/vectors/add";
import { addmN } from "@thi.ng/vectors/addmn";
import { direction } from "@thi.ng/vectors/direction";
import { mixN } from "@thi.ng/vectors/mixn";
import { set } from "@thi.ng/vectors/set";
const __buildUniform = (segments, t) => {
  const res = [];
  for (let i = 0, n = segments.length - 2; i < n; i += 2) {
    const a = segments[i];
    const b = segments[i + 1];
    const c = segments[i + 2];
    res.push([
      a,
      add(null, direction([], a, b, t), a),
      add(null, direction([], c, b, t), c),
      c
    ]);
  }
  return res;
};
const __buildNonUniform = (segments, t) => {
  const res = [];
  for (let i = 0, n = segments.length - 2; i < n; i += 2) {
    const a = segments[i];
    const b = segments[i + 1];
    const c = segments[i + 2];
    res.push([a, mixN([], a, b, t), mixN([], c, b, t), c]);
  }
  return res;
};
const closedCubicFromControlPoints = (points, t = 1, uniform = false) => {
  const segments = [];
  for (let i = 0, num = points.length; i < num; i++) {
    const q = points[(i + 1) % num];
    segments.push(addmN([], points[i], q, 0.5), set([], q));
  }
  segments.push(segments[0]);
  return uniform ? __buildUniform(segments, t) : __buildNonUniform(segments, t);
};
const openCubicFromControlPoints = (points, t = 1, uniform = false) => {
  const segments = [set([], points[0]), set([], points[0])];
  const num = points.length - 1;
  for (let i = 0; i < num; i++) {
    const q = points[i + 1];
    segments.push(addmN([], points[i], q, 0.5), set([], q));
  }
  segments.push(set([], points[num]));
  return uniform ? __buildUniform(segments, t) : __buildNonUniform(segments, t);
};
export {
  closedCubicFromControlPoints,
  openCubicFromControlPoints
};