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add an update method for iterative algorithms (#48)
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closes #36
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@mourner
mourner committed Jun 18, 2019
1 parent a89e7c9 commit 7432140
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5 changes: 5 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,11 @@ A `Uint32Array` array of indices that reference points on the convex hull of the
An array of input coordinates in the form `[x0, y0, x1, y1, ....]`,
of the type provided in the constructor (or `Float64Array` if you used `Delaunator.from`).

#### delaunay.update()

Updates the triangulation if you modified `delaunay.coords` values in place, avoiding expensive memory allocations.
Useful for iterative relaxation algorithms such as [Lloyd's](https://en.wikipedia.org/wiki/Lloyd%27s_algorithm).

## Performance

Benchmark results against other Delaunay JS libraries
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82 changes: 45 additions & 37 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -25,18 +25,28 @@ export default class Delaunator {

// arrays that will store the triangulation graph
const maxTriangles = Math.max(2 * n - 5, 0);
const triangles = this.triangles = new Uint32Array(maxTriangles * 3);
const halfedges = this.halfedges = new Int32Array(maxTriangles * 3);
this._triangles = new Uint32Array(maxTriangles * 3);
this._halfedges = 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 = new Int32Array(this._hashSize).fill(-1); // angular edge hash
this._hullPrev = new Uint32Array(n); // edge to prev edge
this._hullNext = new Uint32Array(n); // edge to next edge
this._hullTri = new Uint32Array(n); // edge to adjacent triangle
this._hullHash = new Int32Array(this._hashSize).fill(-1); // angular edge hash

// temporary arrays for sorting points
this._ids = new Uint32Array(n);
this._dists = new Float64Array(n);

this.update();
}

update() {
const {coords, _hullPrev: hullPrev, _hullNext: hullNext, _hullTri: hullTri, _hullHash: hullHash} = this;
const n = coords.length >> 1;

// populate an array of point indices; calculate input data bbox
const ids = new Uint32Array(n);
let minX = Infinity;
let minY = Infinity;
let maxX = -Infinity;
Expand All @@ -49,7 +59,7 @@ export default class Delaunator {
if (y < minY) minY = y;
if (x > maxX) maxX = x;
if (y > maxY) maxY = y;
ids[i] = i;
this._ids[i] = i;
}
const cx = (minX + maxX) / 2;
const cy = (minY + maxY) / 2;
Expand Down Expand Up @@ -99,23 +109,22 @@ export default class Delaunator {
if (minRadius === Infinity) {
// order collinear points by dx (or dy if all x are identical)
// and return the list as a hull
const x0 = coords[0], y0 = coords[1], dx = new Float64Array(n);
for (let i = 0; i < n; i++) {
dx[i] = coords[2 * i] - x0 || coords[2 * i + 1] - y0;
this._dists[i] = (coords[2 * i] - coords[0]) || (coords[2 * i + 1] - coords[1]);
}
quicksort(ids, dx, 0, n - 1);
quicksort(this._ids, this._dists, 0, n - 1);
const hull = new Uint32Array(n);
let j = 0;
for (let i = 0, d0 = -Infinity; i < n; i++) {
if (dx[ids[i]] > d0) {
hull[j++] = ids[i];
d0 = dx[ids[i]];
const id = this._ids[i];
if (this._dists[id] > d0) {
hull[j++] = id;
d0 = this._dists[id];
}
}
this.hull = hull.subarray(0, j);
this.triangles = new Uint32Array(0);
this.halfedges = new Uint32Array(0);
this._hashSize = this.hullPrev = this.hullNext = this.hullTri = null;
return;
}

Expand All @@ -136,16 +145,15 @@ export default class Delaunator {
this._cx = center.x;
this._cy = center.y;

const 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);
this._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);
quicksort(this._ids, this._dists, 0, n - 1);

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

hullNext[i0] = hullPrev[i2] = i1;
Expand All @@ -156,15 +164,16 @@ export default class Delaunator {
hullTri[i1] = 1;
hullTri[i2] = 2;

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

Expand Down Expand Up @@ -225,7 +234,7 @@ export default class Delaunator {
}

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

Expand All @@ -235,23 +244,22 @@ export default class Delaunator {
}

this.hull = new Uint32Array(hullSize);
for (let i = 0, e = this.hullStart; i < hullSize; i++) {
for (let i = 0, e = this._hullStart; i < hullSize; i++) {
this.hull[i] = e;
e = hullNext[e];
}
this.hullPrev = this.hullNext = this.hullTri = null; // get rid of temporary arrays

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

_hashKey(x, y) {
return Math.floor(pseudoAngle(x - this._cx, y - this._cy) * this._hashSize) % this._hashSize;
}

_legalize(a) {
const {triangles, coords, halfedges} = this;
const {_triangles: triangles, _halfedges: halfedges, coords} = this;

let i = 0;
let ar = 0;
Expand Down Expand Up @@ -307,14 +315,14 @@ export default class Delaunator {

// edge swapped on the other side of the hull (rare); fix the halfedge reference
if (hbl === -1) {
let e = this.hullStart;
let e = this._hullStart;
do {
if (this.hullTri[e] === bl) {
this.hullTri[e] = a;
if (this._hullTri[e] === bl) {
this._hullTri[e] = a;
break;
}
e = this.hullNext[e];
} while (e !== this.hullStart);
e = this._hullNext[e];
} while (e !== this._hullStart);
}
this._link(a, hbl);
this._link(b, halfedges[ar]);
Expand All @@ -336,17 +344,17 @@ export default class Delaunator {
}

_link(a, b) {
this.halfedges[a] = b;
if (b !== -1) this.halfedges[b] = a;
this._halfedges[a] = b;
if (b !== -1) this._halfedges[b] = a;
}

// add a new triangle given vertex indices and adjacent half-edge ids
_addTriangle(i0, i1, i2, a, b, c) {
const t = this.trianglesLen;

this.triangles[t] = i0;
this.triangles[t + 1] = i1;
this.triangles[t + 2] = i2;
this._triangles[t] = i0;
this._triangles[t + 1] = i1;
this._triangles[t + 2] = i2;

this._link(t, a);
this._link(t + 1, b);
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22 changes: 19 additions & 3 deletions test.js
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