use grid index instead of rtree for querying features

Why?
Both indexes have comparable querying performance and Grid is
transferrable. Insertion is faster with Grid than rbush but that's not
the main benefit.

Point queries are really fast for both. Each is sometimes faster than
the other. Therre is no clear winner.

Large, full-screen bbox queries are 10% slower with Grid than rbush but
difference is not significant (0.2% of FeatureTree.query).

comparisons were done with mapbox-streets-v6

js/data/feature_tree.js

@@ -1,6 +1,5 @@
 'use strict';
 
-var rbush = require('rbush');
 var Point = require('point-geometry');
 var util = require('../util/util');
 var loadGeometry = require('./load_geometry');
@@ -25,7 +24,6 @@ function FeatureTree(coord, overscaling, collisionTile, vtLayers) {
     this.x = coord.x;
     this.y = coord.y;
     this.z = coord.z - Math.log(overscaling) / Math.LN2;
-    this.rtree = rbush(9);
     this.toBeInserted = [];
     this.grid = new Grid(16, EXTENT, 0);
     this.featureIndexArray = new FeatureIndexArray();
@@ -40,19 +38,8 @@ FeatureTree.prototype.insert = function(bbox, extent, featureIndex, sourceLayerI
     bbox[1] *= scale;
     bbox[2] *= scale;
     bbox[3] *= scale;
-    bbox.key = this.featureIndexArray.length;
+    this.grid.insert(this.featureIndexArray.length, bbox[0], bbox[1], bbox[2], bbox[3]);
     this.featureIndexArray.emplaceBack(featureIndex, sourceLayerIndex, bucketIndex);
-    this.toBeInserted.push(bbox);
-};
-
-// bulk insert into tree
-FeatureTree.prototype._load = function() {
-    this.rtree.load(this.toBeInserted);
-    for (var i = 0; i < this.toBeInserted.length; i++) {
-        var bbox = this.toBeInserted[i];
-        this.grid.insert(i, bbox[0], bbox[1], bbox[2], bbox[3]);
-    }
-    this.toBeInserted = [];
 };
 
 FeatureTree.prototype.setCollisionTile = function(collisionTile) {
@@ -66,7 +53,6 @@ function translateDistance(translate) {
 // Finds features in this tile at a particular position.
 FeatureTree.prototype.query = function(args, styleLayersByID) {
     if (!this.vtLayers) return [];
-    if (this.toBeInserted.length) this._load();
 
     var params = args.params || {},
         pixelsToTileUnits = EXTENT / args.tileSize / args.scale,
@@ -108,15 +94,10 @@ FeatureTree.prototype.query = function(args, styleLayersByID) {
         maxY = Math.max(maxY, p.y);
     }
 
-    var bounds = [minX - additionalRadius, minY - additionalRadius, maxX + additionalRadius, maxY + additionalRadius];
-    var treeMatching = this.rtree.search(bounds);
-
     var matching = this.grid.query(minX - additionalRadius, minY - additionalRadius, maxX + additionalRadius, maxY + additionalRadius);
     var match = this.featureIndexArray.at(0);
     filterMatching.call(this, matching, match);
 
-    if (matching.length !== treeMatching.length) throw Error("asdf");
-
     var matchingSymbols = this.collisionTile.queryRenderedSymbols(minX, minY, maxX, maxY, args.scale);
     var match2 = this.collisionTile.collisionBoxArray.at(0);
     filterMatching.call(this, matchingSymbols, match2);

package.json

@@ -21,7 +21,6 @@
     "pbf": "^1.3.2",
     "pngjs": "^2.2.0",
     "point-geometry": "^0.0.0",
-    "rbush": "^1.4.0",
     "request": "^2.39.0",
     "resolve-url": "^0.2.1",
     "supercluster": "^2.0.0",