From 3a2e5afa57d36e40ea75aaf66560fb272bec54cf Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philippe=20Rivi=C3=A8re?= <fil@rezo.net>
Date: Sat, 25 Mar 2023 15:21:52 +0100
Subject: [PATCH 1/2] fix #141

---
 src/voronoi.js       | 21 ++++++++++-----------
 test/voronoi-test.js |  6 ++++++
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/src/voronoi.js b/src/voronoi.js
index 8811bfe..fcd7e0c 100644
--- a/src/voronoi.js
+++ b/src/voronoi.js
@@ -18,6 +18,7 @@ export default class Voronoi {
   }
   _init() {
     const {delaunay: {points, hull, triangles}, vectors} = this;
+    let b; // lazily computed barycenter of the hull
 
     // Compute circumcenters.
     const circumcenters = this.circumcenters = this._circumcenters.subarray(0, triangles.length / 3 * 2);
@@ -39,17 +40,15 @@ export default class Voronoi {
       const ab = (dx * ey - dy * ex) * 2;
 
       if (Math.abs(ab) < 1e-9) {
-        // degenerate case (collinear diagram)
-        // almost equal points (degenerate triangle)
-        // the circumcenter is at the infinity, in a
-        // direction that is:
-        // 1. orthogonal to the halfedge.
-        let a = 1e9;
-        // 2. points away from the center; since the list of triangles starts
-        // in the center, the first point of the first triangle
-        // will be our reference
-        const r = triangles[0] * 2;
-        a *= Math.sign((points[r] - x1) * ey - (points[r + 1] - y1) * ex);
+        // For a degenerate triangle, the circumcenter is at the infinity, in a
+        // direction orthogonal to the halfedge and away from the “center” of
+        // the diagram <bx, by>, defined as the hull’s barycenter.
+        if (!b) {
+          b = {x: 0, y: 0};
+          for (const i of hull) b.x += points[i * 2], b.y += points[i * 2 + 1];
+          b.x /= hull.length, b.y /= hull.length;
+        }
+        const a = 1e9 * Math.sign((b.x - x1) * ey - (b.y - y1) * ex);
         x = (x1 + x3) / 2 - a * ey;
         y = (y1 + y3) / 2 + a * ex;
       } else {
diff --git a/test/voronoi-test.js b/test/voronoi-test.js
index 129c392..dcf0f09 100644
--- a/test/voronoi-test.js
+++ b/test/voronoi-test.js
@@ -122,3 +122,9 @@ it("voronoi returns the expected result (#136)", () => {
   const voronoi = Delaunay.from(points).voronoi([0, 0, 1000, 1000]);
   assert.strictEqual(voronoi.cellPolygon(3).length, 6);
 });
+
+it("voronoi returns the expected result (#141)", () => {
+  const points = [[10, 190]].concat(Array.from({ length: 7 }, (d, i) => [i * 80, (i * 50) / 7]));
+  const voronoi = Delaunay.from(points).voronoi([1, 1, 499, 199]);
+  assert.deepEqual(Array.from(voronoi.cellPolygons(), (d) => d.length), [7, 5, 5, 5, 6, 5, 5, 5]);
+});

From e11a0cd7320a0bad638c283851f29a06c39b37a8 Mon Sep 17 00:00:00 2001
From: Mike Bostock <mbostock@gmail.com>
Date: Fri, 31 Mar 2023 19:38:00 -0700
Subject: [PATCH 2/2] bx, by

---
 src/voronoi.js | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/voronoi.js b/src/voronoi.js
index fcd7e0c..4918036 100644
--- a/src/voronoi.js
+++ b/src/voronoi.js
@@ -18,7 +18,7 @@ export default class Voronoi {
   }
   _init() {
     const {delaunay: {points, hull, triangles}, vectors} = this;
-    let b; // lazily computed barycenter of the hull
+    let bx, by; // lazily computed barycenter of the hull
 
     // Compute circumcenters.
     const circumcenters = this.circumcenters = this._circumcenters.subarray(0, triangles.length / 3 * 2);
@@ -43,12 +43,12 @@ export default class Voronoi {
         // For a degenerate triangle, the circumcenter is at the infinity, in a
         // direction orthogonal to the halfedge and away from the “center” of
         // the diagram <bx, by>, defined as the hull’s barycenter.
-        if (!b) {
-          b = {x: 0, y: 0};
-          for (const i of hull) b.x += points[i * 2], b.y += points[i * 2 + 1];
-          b.x /= hull.length, b.y /= hull.length;
+        if (bx === undefined) {
+          bx = by = 0;
+          for (const i of hull) bx += points[i * 2], by += points[i * 2 + 1];
+          bx /= hull.length, by /= hull.length;
         }
-        const a = 1e9 * Math.sign((b.x - x1) * ey - (b.y - y1) * ex);
+        const a = 1e9 * Math.sign((bx - x1) * ey - (by - y1) * ex);
         x = (x1 + x3) / 2 - a * ey;
         y = (y1 + y3) / 2 + a * ex;
       } else {