https://github.com/kyorohiro/hello_skyengine/tree/master/draw_rect
// following code is checked in 2016/01/13import 'package:flutter/widgets.dart';import 'package:flutter/painting.dart';import 'package:flutter/rendering.dart';void main() {runApp(new DrawRectWidget());}class DrawRectWidget extends OneChildRenderObjectWidget {RenderObject createRenderObject() {return new DrawRectObject();}}class DrawRectObject extends RenderBox {void paint(PaintingContext context, Offset offset) {Paint p = new Paint();p.color = new Color.fromARGB(0xff, 0xff, 0xff, 0xff);Rect r = new Rect.fromLTWH(50.0, 100.0, 150.0, 25.0);context.canvas.drawRect(r, p);}}