Fix broken polygon

src/voronoi.js

@@ -193,9 +193,9 @@ export default class Voronoi {
     if (points === null) return null;
     const {vectors: V} = this;
     const v = i * 4;
-    return V[v] || V[v + 1]
+    return this._simplify(V[v] || V[v + 1]
         ? this._clipInfinite(i, points, V[v], V[v + 1], V[v + 2], V[v + 3])
-        : this._clipFinite(i, points);
+        : this._clipFinite(i, points));
   }
   _clipFinite(i, points) {
     const n = points.length;
@@ -286,14 +286,6 @@ export default class Voronoi {
         P.splice(j, 0, x, y), j += 2;
       }
     }
-    if (P.length > 4) {
-      for (let i = 0; i < P.length; i+= 2) {
-        const j = (i + 2) % P.length, k = (i + 4) % P.length;
-        if (P[i] === P[j] && P[j] === P[k]
-        || P[i + 1] === P[j + 1] && P[j + 1] === P[k + 1])
-          P.splice(j, 2), i -= 2;
-      }
-    }
     return j;
   }
   _project(x0, y0, vx, vy) {
@@ -326,4 +318,16 @@ export default class Voronoi {
         | (y < this.ymin ? 0b0100
         : y > this.ymax ? 0b1000 : 0b0000);
   }
+  _simplify(P) {
+    if (P && P.length > 4) {
+      for (let i = 0; i < P.length; i+= 2) {
+        const j = (i + 2) % P.length, k = (i + 4) % P.length;
+        if (P[i] === P[j] && P[j] === P[k] || P[i + 1] === P[j + 1] && P[j + 1] === P[k + 1]) {
+          P.splice(j, 2), i -= 2;
+        }
+      }
+      if (!P.length) P = null;
+    }
+    return P;
+  }
 }

test/voronoi-test.js

@@ -79,7 +79,7 @@ it("cellPolygons filter out empty cells and have the cell index as a property",
   const voronoi = Delaunay.from(pts).voronoi([0, 0, 2, 2]);
   assert.deepStrictEqual([...voronoi.cellPolygons()], [
     Object.assign([[0, 0], [1, 0], [0, 1], [0, 0]], {index:0, }),
-    Object.assign([[0, 1], [1, 0], [2, 0], [2, 2], [0, 2], [0, 1]], { index: 2 })
+    Object.assign([[2, 2], [0, 2], [0, 1], [1, 0], [2, 0], [2, 2]], { index: 2 })
   ]);
 });
 
@@ -106,3 +106,19 @@ it("voronoi.neighbors returns the correct neighbors, rotated", () => {
   const voronoi = Delaunay.from(points).voronoi([-100, -90, 0, 0]);
   assert.deepStrictEqual([0, 1, 2, 3].map(i => [...voronoi.neighbors(i)].sort()), [[1], [0, 2, 3], [1, 3], [1, 2]]);
 });
+
+it("voronoi returns the expected result (#136)", () => {
+  const points = [
+    [447.27981036477433, 698.9400262172304],
+    [485.27830313288746, 668.9946483670656],
+    [611.9525697080425, 397.71056371206487],
+    [491.44637766366105, 692.071157339428],
+    [697.553622336339, 692.071157339428],
+    [497.00778156318086, 667.1990851383492],
+    [691.9922184368191, 667.1990851383492],
+    [544.9897579870977, 407.0828550310619],
+    [543.1738215956482, 437.35879519252677]
+  ];
+  const voronoi = Delaunay.from(points).voronoi([0, 0, 1000, 1000]);
+  assert.strictEqual(voronoi.cellPolygon(3).length, 6);
+});