Fix small-radius clusters not always forming on higher zooms

index.js

@@ -20,6 +20,8 @@ const defaultOptions = {
     map: props => props // props => ({sum: props.my_value})
 };
 
+const fround = Math.fround || (tmp => (x => (tmp[0] = +x)))(new Float32Array(1));
+
 export default class Supercluster {
     constructor(options) {
         this.options = extend(Object.create(defaultOptions), options);
@@ -323,8 +325,8 @@ export default class Supercluster {
 
 function createCluster(x, y, id, numPoints, properties) {
     return {
-        x, // weighted cluster center
-        y,
+        x: fround(x), // weighted cluster center; round for consistency with Float32Array index
+        y: fround(y),
         zoom: Infinity, // the last zoom the cluster was processed at
         id, // encodes index of the first child of the cluster and its zoom level
         parentId: -1, // parent cluster id
@@ -336,8 +338,8 @@ function createCluster(x, y, id, numPoints, properties) {
 function createPointCluster(p, id) {
     const [x, y] = p.geometry.coordinates;
     return {
-        x: lngX(x), // projected point coordinates
-        y: latY(y),
+        x: fround(lngX(x)), // projected point coordinates
+        y: fround(latY(y)),
         zoom: Infinity, // the last zoom the point was processed at
         index: id, // index of the source feature in the original input array,
         parentId: -1 // parent cluster id

test/test.js

@@ -157,3 +157,18 @@ test('does not crash on weird bbox values', (t) => {
     t.end();
 });
 
+test('makes sure same-location points are clustered', (t) => {
+    const index = new Supercluster({
+        maxZoom: 20,
+        extent: 8192,
+        radius: 16,
+        log: true
+    }).load([
+        {type: 'Feature', geometry: {type: 'Point', coordinates: [-1.426798, 53.943034]}},
+        {type: 'Feature', geometry: {type: 'Point', coordinates: [-1.426798, 53.943034]}}
+    ]);
+
+    t.equal(index.trees[20].ids.length, 1);
+
+    t.end();
+});