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:html';
+import 'dart:async';
+
+abstract class Renderable {
+  render();
+}
+
+typedef void RenderingCallback();
+
+abstract class AsyncRenderable extends Renderable {
+  Future<RenderingCallback> render();
+}
+
+class RenderedEvent<T> {
+  final T element;
+  final bool otherRenderScheduled;
+  RenderedEvent(this.element, this.otherRenderScheduled);
+}
+
+class RenderingScheduler<T extends Renderable> {
+  bool _dirty = false;
+  bool _scheduledRendering = false;
+  bool _scheduledNotification = false;
+  final T element;
+
+  final StreamController<RenderedEvent<T>> _onRendered;
+  final Stream<RenderedEvent<T>> onRendered;
+
+  factory RenderingScheduler(T element) {
+    assert(element != null);
+    var controller = new StreamController<RenderedEvent<T>>();
+    var stream = controller.stream.asBroadcastStream();
+    return new RenderingScheduler<T>._(element, controller, stream);
+  }
+
+  RenderingScheduler._(this.element, this._onRendered, this.onRendered);
+
+  void dirty() {
+    if (_dirty) return;
+    _dirty = true;
+    scheduleRendering();
+  }
+
+  void scheduleRendering() {
+    if (_scheduledRendering) return;
+    _render();
+    _scheduledRendering = true;
+  }
+
+  Future _render() async {
+    _dirty = false;
+    RenderingCallback render;
+    if (element is AsyncRenderable) {
+      render = await element.render();

[Cutch, 2016/07/12 16:24:36]

just have one animationframe callback and render all elements that are dirty

+    } else {
+      render = element.render;
+    }
+    await window.animationFrame;
+    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;
+  }
+}