anchor.diff:   * https://github.com/martinsik/dart-webgl-tutorials
    */
   class TwoBarrels {
  -
  +  static const double MOUSE_SENSITIVITY = 0.5; // Multiplier for mouse x movements
     CanvasElement _canvas;
     webgl.RenderingContext _gl;
     webgl.Program _shaderProgram;
  
positive.code:     // move
      _animate(time);
      _handleKeys();
  
      // keep drawing
      window.requestAnimationFrame(this.render);
  
negative.code:       player.movement.add(a.transform(player.rotation.clone()).scale(-0.0001));
      }
      if (pressed(81)) { //q
        Matrix2 a = new Matrix2.rotation(radians(1.0));
        player.rotation = a.transform(player.rotation.clone()); 
      }
      if (pressed(69)) { //e
        Matrix2 a = new Matrix2.rotation(radians(-1.0));
        player.rotation = a.transform(player.rotation.clone());
      }
  