docs: function fromScreen(pos){
        var x = pos.x;
        var y = pos.y;
        var w = width;
        var h = height;
        
        var left = -2;
        var right = 2;
        var top = -2;
        var bottom = 2;
        
        var d = 4;
        
        return {
          x: x/w * d + left,
          y: y/h * d + right
        };
      }