fix a bug when updating to collinear points

as delaunay.update did not go through the collinearity check, it failed when we created a delaunay and then updated it to collinear points

live test case https://observablehq.com/d/58b705d93bc8524a

Author: Fil

src/delaunay.js

@@ -35,9 +35,21 @@ function jitter(x, y, r) {
 
 export default class Delaunay {
   constructor(points) {
-    let d = new Delaunator(points),
-      a = area(d.hull, points);
-    if (a < 1e-10 && d.hull && d.hull.length > 2) {
+    this._delaunator = new Delaunator(points);
+    this.inedges = new Int32Array(points.length / 2);
+    this._hullIndex = new Int32Array(points.length / 2);
+    this.points = this._delaunator.coords;
+    this._init();
+  }
+  update() {
+    this._delaunator.update();
+    this._init();
+  }
+  _init() {
+    const d = this._delaunator, points = this.points;
+
+    // check for collinear
+    if (d.hull && d.hull.length > 2 && area(d.hull, points) < 1e-10) {
       this.collinear = Int32Array.from({length: points.length/2}, (_,i) => i)
         .sort((i, j) => points[2 * i] - points[2 * j] || points[2 * i + 1] - points[2 * j + 1]); // for exact neighbors
       const e = this.collinear[0], f = this.collinear[this.collinear.length - 1],
@@ -48,19 +60,11 @@ export default class Delaunay {
         points[2 * i] = p[0];
         points[2 * i + 1] = p[1];
       }
-      d = new Delaunator(points);
+      this._delaunator = new Delaunator(points);
+    } else {
+      delete this.collinear;
     }
-    this._delaunator = d;
-    this.inedges = new Int32Array(points.length / 2);
-    this._hullIndex = new Int32Array(points.length / 2);
-    this.points = this._delaunator.coords;
-    this._init();
-  }
-  update() {
-    this._delaunator.update();
-    this._init();
-  }
-  _init() {
+
     const halfedges = this.halfedges = this._delaunator.halfedges;
     const hull = this.hull = this._delaunator.hull;
     const triangles = this.triangles = this._delaunator.triangles;

test/delaunay-test.js

@@ -125,6 +125,27 @@ tape("delaunay.update() allows fast updates", test => {
   test.deepEqual(circumcenters2, Float64Array.from([ -150, 50, -250, -150, 50, -150, -150, -250 ]));
 });
 
+tape("delaunay.update() updates collinear points", test => {
+  const delaunay = new Delaunay(Array.from({ length: 250 }).fill(0));
+  test.equal(delaunay.collinear, undefined);
+  for (let i = 0; i < delaunay.points.length; i++)
+    delaunay.points[i] = (i % 2) ? i : 0;
+  delaunay.update();
+  test.equal(delaunay.collinear.length, 125);
+  for (let i = 0; i < delaunay.points.length; i++)
+    delaunay.points[i] = Math.sin(i);
+  delaunay.update();
+  test.equal(delaunay.collinear, undefined);
+  for (let i = 0; i < delaunay.points.length; i++)
+    delaunay.points[i] = (i % 2) ? i : 0;
+  delaunay.update();
+  test.equal(delaunay.collinear.length, 125);
+  for (let i = 0; i < delaunay.points.length; i++)
+    delaunay.points[i] = 0;
+  delaunay.update();
+  test.equal(delaunay.collinear, undefined);
+});
+
 tape("delaunay.find(x, y) with coincident point", test => {
   let delaunay = Delaunay.from([[0, 0], [0, 0], [10,10], [10, -10]]);
   test.equal(delaunay.find(100,100), 2);