avoid spurious points in the corners (#88)

d3 · Sep 4, 2019 · 452c31f · 452c31f
1 parent 056387f
commit 452c31f
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diff --git a/src/voronoi.js b/src/voronoi.js
@@ -258,6 +258,14 @@ 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) {

diff --git a/test/voronoi-test.js b/test/voronoi-test.js
@@ -51,6 +51,17 @@ tape("zero-length edges are removed", test => {
    test.deepEqual(voronoi2.cellPolygon(0), [[15, 20], [0, 20], [0, 0], [15, 0], [15, 20]]);
 });
 
+tape("unnecessary points on the corners are avoided (#88)", test => {
+  for (const [points, lengths] of [
+    [ [[289,25],[3,22],[93,165],[282,184],[65,89]], [ 6, 4, 6, 5, 6 ] ],
+    [ [[189,13],[197,26],[47,133],[125,77],[288,15]], [ 4, 6, 5, 6, 5 ] ],
+    [ [[44,42],[210,193],[113,103],[185,43],[184,37]], [ 5, 5, 7, 5, 6 ]]
+  ]) {
+    const voronoi = Delaunay.from(points).voronoi([0, 0, 290, 190]);
+    test.deepEqual([...voronoi.cellPolygons()].map(d => d.length), lengths);
+  }
+});
+
 tape("a degenerate triangle is avoided", test => {
   const pts = [[424.75, 253.75],[424.75, 253.74999999999997],[407.17640687119285, 296.17640687119285],[364.75, 313.75],[322.32359312880715, 296.17640687119285],[304.75, 253.75],[322.32359312880715, 211.32359312880715],[364.75, 193.75],[407.17640687119285, 211.32359312880715],[624.75, 253.75],[607.1764068711929, 296.17640687119285],[564.75, 313.75],[522.3235931288071, 296.17640687119285],[504.75, 253.75],[564.75, 193.75]
   ]