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