Bar graph added.

node_modules/vega-scenegraph/src/Scenegraph.js

@@ -0,0 +1,54 @@
+import Bounds from './Bounds';
+import GroupItem from './GroupItem';
+import {sceneFromJSON, sceneToJSON} from './util/serialize';
+
+export default function Scenegraph(scene) {
+  if (arguments.length) {
+    this.root = sceneFromJSON(scene);
+  } else {
+    this.root = createMark({
+      marktype: 'group',
+      name: 'root',
+      role: 'frame'
+    });
+    this.root.items = [new GroupItem(this.root)];
+  }
+}
+
+var prototype = Scenegraph.prototype;
+
+prototype.toJSON = function(indent) {
+  return sceneToJSON(this.root, indent || 0);
+};
+
+prototype.mark = function(markdef, group, index) {
+  group = group || this.root.items[0];
+  var mark = createMark(markdef, group);
+  group.items[index] = mark;
+  if (mark.zindex) mark.group.zdirty = true;
+  return mark;
+};
+
+function createMark(def, group) {
+  const mark = {
+    bounds:      new Bounds(),
+    clip:        !!def.clip,
+    group:       group,
+    interactive: def.interactive === false ? false : true,
+    items:       [],
+    marktype:    def.marktype,
+    name:        def.name || undefined,
+    role:        def.role || undefined,
+    zindex:      def.zindex || 0
+  };
+
+  // add accessibility properties if defined
+  if (def.aria != null) {
+    mark.aria = def.aria;
+  }
+  if (def.description) {
+    mark.description = def.description;
+  }
+
+  return mark;
+}