Update function

Delaunator.js

  constructor(coords) {
    const n = coords.length >> 1;
    if (n > 0 && typeof coords[0] !== 'number') throw new Error('Expected coords to contain numbers.');

    this.coords = coords;

    // arrays that will store the triangulation graph
    const maxTriangles = 2 * n - 5;
    const triangles = this.triangles = this.trianglesRaw = new Uint32Array(maxTriangles * 3);
    const halfedges = this.halfedges = this.halfedgesRaw = new Int32Array(maxTriangles * 3);

    // temporary arrays for tracking the edges of the advancing convex hull
    this._hashSize = Math.ceil(Math.sqrt(n));
    const hullPrev = this.hullPrev = new Uint32Array(n); // edge to prev edge
    const hullNext = this.hullNext = new Uint32Array(n); // edge to next edge
    const hullTri = this.hullTri = new Uint32Array(n); // edge to adjacent triangle
    const hullHash = this.hullHash = new Int32Array(this._hashSize).fill(-1); // angular edge hash

    // populate an array of point indices; calculate input data bbox
    const ids = this.ids = new Uint32Array(n);
    let minX = Infinity;
    let minY = Infinity;
    let maxX = -Infinity;
    let maxY = -Infinity;

    for (let i = 0; i < n; i++) {
      const x = coords[2 * i];
      const y = coords[2 * i + 1];
      if (x < minX) minX = x;
      if (y < minY) minY = y;
      if (x > maxX) maxX = x;
      if (y > maxY) maxY = y;
      ids[i] = i;
    }
    const cx = (minX + maxX) / 2;
    const cy = (minY + maxY) / 2;

    let minDist = Infinity;
    let i0, i1, i2;

    // pick a seed point close to the center
    for (let i = 0; i < n; i++) {
      const d = dist(cx, cy, coords[2 * i], coords[2 * i + 1]);
      if (d < minDist) {
        i0 = i;
        minDist = d;
      }
    }
    const i0x = coords[2 * i0];
    const i0y = coords[2 * i0 + 1];

    minDist = Infinity;

    // find the point closest to the seed
    for (let i = 0; i < n; i++) {
      if (i === i0) continue;
      const d = dist(i0x, i0y, coords[2 * i], coords[2 * i + 1]);
      if (d < minDist && d > 0) {
        i1 = i;
        minDist = d;
      }
    }
    let i1x = coords[2 * i1];
    let i1y = coords[2 * i1 + 1];

    let minRadius = Infinity;

    // find the third point which forms the smallest circumcircle with the first two
    for (let i = 0; i < n; i++) {
      if (i === i0 || i === i1) continue;
      const r = circumradius(i0x, i0y, i1x, i1y, coords[2 * i], coords[2 * i + 1]);
      if (r < minRadius) {
        i2 = i;
        minRadius = r;
      }
    }
    let i2x = coords[2 * i2];
    let i2y = coords[2 * i2 + 1];

    if (minRadius === Infinity) {
      throw new Error('No Delaunay triangulation exists for this input.');
    }

    // swap the order of the seed points for counter-clockwise orientation
    if (orient(i0x, i0y, i1x, i1y, i2x, i2y)) {
      const i = i1;
      const x = i1x;
      const y = i1y;
      i1 = i2;
      i1x = i2x;
      i1y = i2y;
      i2 = i;
      i2x = x;
      i2y = y;
    }

    const center = circumcenter(i0x, i0y, i1x, i1y, i2x, i2y);
    this._cx = center.x;
    this._cy = center.y;

    const dists = this.dists = new Float64Array(n);
    for (let i = 0; i < n; i++) {
      dists[i] = dist(coords[2 * i], coords[2 * i + 1], center.x, center.y);
    }

    // sort the points by distance from the seed triangle circumcenter
    quicksort(ids, dists, 0, n - 1);

    // set up the seed triangle as the starting hull
    this.hullStart = i0;
    let hullSize = 3;

    hullNext[i0] = hullPrev[i2] = i1;
    hullNext[i1] = hullPrev[i0] = i2;
    hullNext[i2] = hullPrev[i1] = i0;

    hullTri[i0] = 0;
    hullTri[i1] = 1;
    hullTri[i2] = 2;

    hullHash[this._hashKey(i0x, i0y)] = i0;
    hullHash[this._hashKey(i1x, i1y)] = i1;
    hullHash[this._hashKey(i2x, i2y)] = i2;

    this.trianglesLen = 0;
    this._addTriangle(i0, i1, i2, -1, -1, -1);

    for (let k = 0, xp, yp; k < ids.length; k++) {
      const i = ids[k];
      const x = coords[2 * i];
      const y = coords[2 * i + 1];

      // skip near-duplicate points
      if (k > 0 && Math.abs(x - xp) <= EPSILON && Math.abs(y - yp) <= EPSILON) continue;
      xp = x;
      yp = y;

      // skip seed triangle points
      if (i === i0 || i === i1 || i === i2) continue;

      // find a visible edge on the convex hull using edge hash
      let start = 0;
      for (let j = 0, key = this._hashKey(x, y); j < this._hashSize; j++) {
        start = hullHash[(key + j) % this._hashSize];
        if (start !== -1 && start !== hullNext[start]) break;
      }

      start = hullPrev[start];
      let e = start, q;
      while (q = hullNext[e], !orient(x, y, coords[2 * e], coords[2 * e + 1], coords[2 * q], coords[2 * q + 1])) {
        e = q;
        if (e === start) {
          e = -1;
          break;
        }
      }
      if (e === -1) continue; // likely a near-duplicate point; skip it

      // add the first triangle from the point
      let t = this._addTriangle(e, i, hullNext[e], -1, -1, hullTri[e]);

      // recursively flip triangles from the point until they satisfy the Delaunay condition
      hullTri[i] = this._legalize(t + 2);
      hullTri[e] = t; // keep track of boundary triangles on the hull
      hullSize++;

      // walk forward through the hull, adding more triangles and flipping recursively
      let n = hullNext[e];
      while (q = hullNext[n], orient(x, y, coords[2 * n], coords[2 * n + 1], coords[2 * q], coords[2 * q + 1])) {
        t = this._addTriangle(n, i, q, hullTri[i], -1, hullTri[n]);
        hullTri[i] = this._legalize(t + 2);
        hullNext[n] = n; // mark as removed
        hullSize--;
        n = q;
      }

      // walk backward from the other side, adding more triangles and flipping
      if (e === start) {
        while (q = hullPrev[e], orient(x, y, coords[2 * q], coords[2 * q + 1], coords[2 * e], coords[2 * e + 1])) {
          t = this._addTriangle(q, i, e, -1, hullTri[e], hullTri[q]);
          this._legalize(t + 2);
          hullTri[q] = t;
          hullNext[e] = e; // mark as removed
          hullSize--;
          e = q;
        }
      }

      // update the hull indices
      this.hullStart = hullPrev[i] = e;
      hullNext[e] = hullPrev[n] = i;
      hullNext[i] = n;

      // save the two new edges in the hash table
      hullHash[this._hashKey(x, y)] = i;
      hullHash[this._hashKey(coords[2 * e], coords[2 * e + 1])] = e;
    }

    this.hull = new Uint32Array(hullSize);
    for (let i = 0, e = this.hullStart; i < hullSize; i++) {
      this.hull[i] = e;
      e = hullNext[e];
    }

    // trim typed triangle mesh arrays
    this.triangles = triangles.subarray(0, this.trianglesLen);
    this.halfedges = halfedges.subarray(0, this.trianglesLen);
  }

  update(coords) {
    const n = coords.length >> 1;
    if (n > 0 && typeof coords[0] !== 'number') throw new Error('Expected coords to contain numbers.');

    if (this.coords.length !== coords) throw new Error('New coordinates must have the same number of points!');

    this.coords = coords;

    // arrays that will store the triangulation graph
    // const maxTriangles = 2 * n - 5;
    const triangles = this.triangles = this.trianglesRaw;
    const halfedges = this.halfedges = this.halfedgesRaw;
    triangles.fill(0);
    halfedges.fill(0);

    // temporary arrays for tracking the edges of the advancing convex hull
    this._hashSize = Math.ceil(Math.sqrt(n));
    const hullPrev = this.hullPrev; // edge to prev edge
    const hullNext = this.hullNext; // edge to next edge
    const hullTri = this.hullTri; // edge to adjacent triangle
    const hullHash = this.hullHash; // angular edge hash
    hullPrev.fill(0);
    hullNext.fill(0);
    hullTri.fill(0);
    hullHash.fill(-1)
    // populate an array of point indices; calculate input data bbox
    const ids = this.ids;
    ids.fill(0);
    let minX = Infinity;
    let minY = Infinity;
    let maxX = -Infinity;
    let maxY = -Infinity;

    for (let i = 0; i < n; i++) {
      const x = coords[2 * i];
      const y = coords[2 * i + 1];
      if (x < minX) minX = x;
      if (y < minY) minY = y;
      if (x > maxX) maxX = x;
      if (y > maxY) maxY = y;
      ids[i] = i;
    }
    const cx = (minX + maxX) / 2;
    const cy = (minY + maxY) / 2;

    let minDist = Infinity;
    let i0, i1, i2;

    // pick a seed point close to the center
    for (let i = 0; i < n; i++) {
      const d = dist(cx, cy, coords[2 * i], coords[2 * i + 1]);
      if (d < minDist) {
        i0 = i;
        minDist = d;
      }
    }
    const i0x = coords[2 * i0];
    const i0y = coords[2 * i0 + 1];

    minDist = Infinity;

    // find the point closest to the seed
    for (let i = 0; i < n; i++) {
      if (i === i0) continue;
      const d = dist(i0x, i0y, coords[2 * i], coords[2 * i + 1]);
      if (d < minDist && d > 0) {
        i1 = i;
        minDist = d;
      }
    }
    let i1x = coords[2 * i1];
    let i1y = coords[2 * i1 + 1];

    let minRadius = Infinity;

    // find the third point which forms the smallest circumcircle with the first two
    for (let i = 0; i < n; i++) {
      if (i === i0 || i === i1) continue;
      const r = circumradius(i0x, i0y, i1x, i1y, coords[2 * i], coords[2 * i + 1]);
      if (r < minRadius) {
        i2 = i;
        minRadius = r;
      }
    }
    let i2x = coords[2 * i2];
    let i2y = coords[2 * i2 + 1];

    if (minRadius === Infinity) {
      throw new Error('No Delaunay triangulation exists for this input.');
    }

    // swap the order of the seed points for counter-clockwise orientation
    if (orient(i0x, i0y, i1x, i1y, i2x, i2y)) {
      const i = i1;
      const x = i1x;
      const y = i1y;
      i1 = i2;
      i1x = i2x;
      i1y = i2y;
      i2 = i;
      i2x = x;
      i2y = y;
    }

    const center = circumcenter(i0x, i0y, i1x, i1y, i2x, i2y);
    this._cx = center.x;
    this._cy = center.y;

    const dists = this.dists;
    for (let i = 0; i < n; i++) {
      dists[i] = dist(coords[2 * i], coords[2 * i + 1], center.x, center.y);
    }

    // sort the points by distance from the seed triangle circumcenter
    quicksort(ids, dists, 0, n - 1);

    // set up the seed triangle as the starting hull
    this.hullStart = i0;
    let hullSize = 3;

    hullNext[i0] = hullPrev[i2] = i1;
    hullNext[i1] = hullPrev[i0] = i2;
    hullNext[i2] = hullPrev[i1] = i0;

    hullTri[i0] = 0;
    hullTri[i1] = 1;
    hullTri[i2] = 2;

    hullHash[this._hashKey(i0x, i0y)] = i0;
    hullHash[this._hashKey(i1x, i1y)] = i1;
    hullHash[this._hashKey(i2x, i2y)] = i2;

    this.trianglesLen = 0;
    this._addTriangle(i0, i1, i2, -1, -1, -1);

    for (let k = 0, xp, yp; k < ids.length; k++) {
      const i = ids[k];
      const x = coords[2 * i];
      const y = coords[2 * i + 1];

      // skip near-duplicate points
      if (k > 0 && Math.abs(x - xp) <= EPSILON && Math.abs(y - yp) <= EPSILON) continue;
      xp = x;
      yp = y;

      // skip seed triangle points
      if (i === i0 || i === i1 || i === i2) continue;

      // find a visible edge on the convex hull using edge hash
      let start = 0;
      for (let j = 0, key = this._hashKey(x, y); j < this._hashSize; j++) {
        start = hullHash[(key + j) % this._hashSize];
        if (start !== -1 && start !== hullNext[start]) break;
      }

      start = hullPrev[start];
      let e = start, q;
      while (q = hullNext[e], !orient(x, y, coords[2 * e], coords[2 * e + 1], coords[2 * q], coords[2 * q + 1])) {
        e = q;
        if (e === start) {
          e = -1;
          break;
        }
      }
      if (e === -1) continue; // likely a near-duplicate point; skip it

      // add the first triangle from the point
      let t = this._addTriangle(e, i, hullNext[e], -1, -1, hullTri[e]);

      // recursively flip triangles from the point until they satisfy the Delaunay condition
      hullTri[i] = this._legalize(t + 2);
      hullTri[e] = t; // keep track of boundary triangles on the hull
      hullSize++;

      // walk forward through the hull, adding more triangles and flipping recursively
      let n = hullNext[e];
      while (q = hullNext[n], orient(x, y, coords[2 * n], coords[2 * n + 1], coords[2 * q], coords[2 * q + 1])) {
        t = this._addTriangle(n, i, q, hullTri[i], -1, hullTri[n]);
        hullTri[i] = this._legalize(t + 2);
        hullNext[n] = n; // mark as removed
        hullSize--;
        n = q;
      }

      // walk backward from the other side, adding more triangles and flipping
      if (e === start) {
        while (q = hullPrev[e], orient(x, y, coords[2 * q], coords[2 * q + 1], coords[2 * e], coords[2 * e + 1])) {
          t = this._addTriangle(q, i, e, -1, hullTri[e], hullTri[q]);
          this._legalize(t + 2);
          hullTri[q] = t;
          hullNext[e] = e; // mark as removed
          hullSize--;
          e = q;
        }
      }

      // update the hull indices
      this.hullStart = hullPrev[i] = e;
      hullNext[e] = hullPrev[n] = i;
      hullNext[i] = n;

      // save the two new edges in the hash table
      hullHash[this._hashKey(x, y)] = i;
      hullHash[this._hashKey(coords[2 * e], coords[2 * e + 1])] = e;
    }

    this.hull = new Uint32Array(hullSize);
    for (let i = 0, e = this.hullStart; i < hullSize; i++) {
      this.hull[i] = e;
      e = hullNext[e];
    }

    // trim typed triangle mesh arrays
    this.triangles = triangles.subarray(0, this.trianglesLen);
    this.halfedges = halfedges.subarray(0, this.trianglesLen);
    return this;
  }