Wrapping leaf nodes in non polymer elements

runtime/observatory/lib/src/elements/helpers/rendering_scheduler.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:observatory/src/elements/helpers/rendering_queue.dart';
+export 'package:observatory/src/elements/helpers/rendering_queue.dart';
+
+abstract class Renderable {
+  void render();
+}
+
+class RenderedEvent<T> {
+  final T element;
+  final bool otherRenderScheduled;
+  RenderedEvent(this.element, this.otherRenderScheduled);
+}
+
+class RenderingScheduler<T extends Renderable> implements RenderingTask {
+  bool _enabled = false;
+  bool _dirty = false;
+  bool _scheduledRendering = false;
+  bool _scheduledNotification = false;
+  final T element;
+  final RenderingQueue queue;
+
+  final StreamController<RenderedEvent<T>> _onRendered;
+  final Stream<RenderedEvent<T>> onRendered;
+
+  factory RenderingScheduler(T element, {RenderingQueue queue}) {
+    assert(element != null);
+    if (queue == null) {
+      queue = new RenderingQueue();
+    }
+    var controller = new StreamController<RenderedEvent<T>>();
+    var stream = controller.stream.asBroadcastStream();
+    return new RenderingScheduler<T>._(element, queue, controller, stream);
+  }
+
+  RenderingScheduler._(this.element, this.queue, this._onRendered,
+                       this.onRendered);
+
+  void enable() {
+    if (_enabled) return;
+    _enabled = true;
+    scheduleRendering();
+  }
+
+  void disable({bool notify: false}) {
+    if (!_enabled) return;
+    _enabled = false;
+    if (notify) scheduleNotification();
+  }
+
+  void dirty() {
+    if (_dirty) return;
+    _dirty = true;
+    scheduleRendering();
+  }
+
+  void scheduleRendering() {
+    if (_scheduledRendering) return;
+    if (!_enabled) return;
+    queue.enqueue(this);
+    _scheduledRendering = true;
+  }
+
+  void render(){
+    if (!_enabled) return;
+    _dirty = false;
+    element.render();
+    _scheduledRendering = false;
+    scheduleNotification();
+    if (_dirty) scheduleRendering();
+  }
+
+  void scheduleNotification() {
+    if (_scheduledNotification) return;
+    _notify();
+    _scheduledNotification = true;
+  }
+
+  Future _notify() async {
+    _onRendered.add(new RenderedEvent<T>(element, _dirty));
+    _scheduledNotification = false;
+  }
+}