Bar graph added.

node_modules/vega-voronoi/src/Voronoi.js

@@ -0,0 +1,60 @@
+import {Transform} from 'vega-dataflow';
+import {inherits} from 'vega-util';
+import {Delaunay} from 'd3-delaunay';
+
+export default function Voronoi(params) {
+  Transform.call(this, null, params);
+}
+
+Voronoi.Definition = {
+  'type': 'Voronoi',
+  'metadata': {'modifies': true},
+  'params': [
+    { 'name': 'x', 'type': 'field', 'required': true },
+    { 'name': 'y', 'type': 'field', 'required': true },
+    { 'name': 'size', 'type': 'number', 'array': true, 'length': 2 },
+    { 'name': 'extent', 'type': 'array', 'array': true, 'length': 2,
+      'default': [[-1e5, -1e5], [1e5, 1e5]],
+      'content': {'type': 'number', 'array': true, 'length': 2} },
+    { 'name': 'as', 'type': 'string', 'default': 'path' }
+  ]
+};
+
+const prototype = inherits(Voronoi, Transform);
+
+const defaultExtent = [-1e5, -1e5, 1e5, 1e5];
+
+prototype.transform = function(_, pulse) {
+  const as = _.as || 'path',
+        data = pulse.source;
+
+  // nothing to do if no data
+  if (!data || !data.length) return pulse;
+
+  // configure and construct voronoi diagram
+  let s = _.size;
+  s = s ? [0, 0, s[0], s[1]]
+    : (s = _.extent) ? [s[0][0], s[0][1], s[1][0], s[1][1]]
+    : defaultExtent;
+
+  const voronoi = this.value = Delaunay.from(data, _.x, _.y).voronoi(s);
+
+  // map polygons to paths
+  for (let i=0, n=data.length; i<n; ++i) {
+    const polygon = voronoi.cellPolygon(i);
+    data[i][as] = polygon ? toPathString(polygon) : null;
+  }
+
+  return pulse.reflow(_.modified()).modifies(as);
+};
+
+// suppress duplicated end point vertices
+function toPathString(p) {
+  const x = p[0][0],
+        y = p[0][1];
+
+  let n = p.length - 1;
+  for (; p[n][0] === x && p[n][1] === y; --n);
+
+  return 'M' + p.slice(0, n + 1).join('L') + 'Z';
+}