anchor.diff:      _gl.uniformMatrix3fv(_uIdentMatrix, false, identMatrix.storage);
     }
   
  -  bool render(double time) {
  +  void render(double time) {
       _gl.viewport(0, 0, _viewportWidth, _viewportHeight);
       _gl.clear(webgl.RenderingContext.COLOR_BUFFER_BIT | webgl.RenderingContext.DEPTH_BUFFER_BIT);
   
  
positive.code: }
  
  void main() {
    Lesson07 lesson = new Lesson07(document.querySelector('#game'));
    lesson.start();
  }
  
negative.code:  * http://learningwebgl.com/blog/?p=571
   * https://github.com/martinsik/dart-webgl-tutorials
   */
  class TwoBarrels {
  
    CanvasElement _canvas;
    webgl.RenderingContext _gl;
  