anchor.diff:    }
   
     void add(Scene s) {
  -    assert (s != null);
  +    assert(s != null);
       _scenes.add(s);
     }
   
  -  void Draw([List<DrawStats> stats = null]) {
  +  void Draw([List<DrawStats> stats]) {
       _framebuffer.Activate(
           _clear_mode, viewPortX, viewPortY, viewPortW, viewPortH);
   
  
positive.code:   int viewPortW = 0;
    int viewPortH = 0;
  
    RenderPhase(String name, this._cgl, [this._framebuffer = null])
        : super(name) {
      if (_framebuffer == null) _framebuffer = new Framebuffer.Screen(_cgl);
    }
  
  
negative.code:   /// @param name
    /// @param this.program
    /// @param unis
    Scene(String name, this.program, [List<UniformGroup> unis])
        : uniforms = unis == null ? <UniformGroup>[] : unis,
          super(name);
  
    void add(Node n) {
      assert(n != null);
      nodes.add(n);
    }
  
    void remove(Node n) {
      nodes.remove(n);
    }
  
    void removeAll() {
      nodes.clear();
    }
  }
  
  void drawRecursively(RenderProgram prog, Node node, final VM.Matrix4 parent,
  