Spinning Square example for the RenderObject API.

sky/examples/rendering/spinning_flex.dart

+// Copyright 2015 The Chromium Authors. 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:sky' as sky;
+import 'dart:math' as math;
+import 'package:vector_math/vector_math.dart';
+import 'package:sky/framework/app.dart';
+import 'package:sky/framework/rendering/box.dart';
+import 'package:sky/framework/rendering/flex.dart';
+import 'package:sky/framework/scheduler.dart';
+import '../lib/solid_color_box.dart';
+
+AppView app;
+double timeBase;
+RenderTransform transformBox;
+
+void main() {
+  RenderFlex flexRoot = new RenderFlex(direction: FlexDirection.vertical);
+
+  void addFlexChildSolidColor(RenderFlex parent, sky.Color backgroundColor, { int flex: 0 }) {
+    RenderSolidColorBox child = new RenderSolidColorBox(backgroundColor);
+    parent.add(child);
+    child.parentData.flex = flex;
+  }
+
+  addFlexChildSolidColor(flexRoot, const sky.Color(0xFFFF00FF), flex: 1);
+  addFlexChildSolidColor(flexRoot, const sky.Color(0xFFFFFF00), flex: 2);
+  addFlexChildSolidColor(flexRoot, const sky.Color(0xFF00FFFF), flex: 1);
+
+  transformBox = new RenderTransform(child: flexRoot, transform: new Matrix4.identity());
+
+  RenderPadding root = new RenderPadding(padding: new EdgeDims.all(20.0), child: transformBox);
+
+  app = new AppView(root);
+
+  addPersistentFrameCallback(rotate);
+}
+
+void rotate(double timeStamp) {
+  if (timeBase == null)
+    timeBase = timeStamp;
+  double delta = (timeStamp - timeBase) / 1000; // radians
+
+  transformBox.setIdentity();
+  transformBox.translate(transformBox.size.width / 2.0, transformBox.size.height / 2.0);
+  transformBox.rotateZ(delta);
+  transformBox.translate(-transformBox.size.width / 2.0, -transformBox.size.height / 2.0);
+}