jsketcher/web/app/brep/topo/edge.js

import {TopoObject} from './topo-object'
import {Vertex} from "./vertex";
import {Point} from "../geom/point";

export class Edge extends TopoObject {

  constructor(curve, a, b) {
    super();
    this.curve = curve;
    this.halfEdge1 = new HalfEdge(this, false, a, b);
    this.halfEdge2 = new HalfEdge(this, true, b, a);
    a.edges.add(this.halfEdge1);
    b.edges.add(this.halfEdge2);
  }

  static fromCurve(curve) {
    const a = new Vertex(curve.point(0));
    const b = new Vertex(curve.point(1));
    return new Edge(curve, a, b);
  }

  invert() {
    const t = this.halfEdge1;
    this.halfEdge1 = this.halfEdge2;
    this.halfEdge2 = t;
    this.halfEdge1.inverted = false;
    this.halfEdge2.inverted = true;
    this.curve = this.curve.invert();
  }
  
  clone() {
    let clone = new Edge(this.curve, this.halfEdge1.vertexA, this.halfEdge1.vertexB);
    Object.assign(clone.data, this.data);
    Object.assign(clone.halfEdge1.data, this.halfEdge1.data);
    Object.assign(clone.halfEdge2.data, this.halfEdge2.data);
    return clone;
  }
}

class HalfEdge extends TopoObject {

  constructor(edge, inverted, a, b) {
    super();
    this.edge = edge;
    this.inverted = inverted;
    this.vertexA = a;
    this.vertexB = b;
    this.loop = null;
    this.next = null;
    this.prev = null;
  }

  twin() {
    return this.edge.halfEdge1 === this ? this.edge.halfEdge2 : this.edge.halfEdge1;
  }

  tangentAtStart() {
    return this.tangent(this.vertexA.point);
  }

  tangentAtEnd() {
    return this.tangent(this.vertexB.point);
  }

  tangent(point) {
    let tangent = this.edge.curve.tangentAtPoint(point);
    tangent._normalize();
    if (this.inverted) {
      tangent._negate();
    }
    return tangent;
  }

  tessellate() {
    let res = this.edge.curve.tessellate.apply(this.edge.curve, arguments);
    if (this.inverted) {
      res = res.slice().reverse();
    }
    return res;
  }
  
  replace(he) {
    if (this.edge.halfEdge1 === this) {
      this.edge.halfEdge1 = he;
    } else {
      this.edge.halfEdge2 = he;
    }

    he.edge = this.edge;
    he.loop = this.loop;
    
    he.prev = this.prev;
    he.prev.next = he;

    he.next = this.next;
    he.next.prev = he;
  }
}