anchor.diff:  
       strokeCanvasLayers();
     }
  -}+}
  
positive.code:       ..on(Message.clearDrawing, (_) => clearDrawing())
        ..on(Message.undoLast, (_) => undoLast())
        ..on(Message.existingCanvasLayers, (x) => existingCanvasLayers(x));
  
    }
  
    drawPoint(DrawPoint drawPoint) {
  
negative.code:     }
    }
  
    clearDrawing() {
      ctx.clearRect(0, 0, canvasWidth, canvasHeight);
  
  