为什么我的路径位置在paper.js中未定义？

Question

我从Chrome中recieving的错误是： Uncaught TypeError: Cannot read property 'position' of undefined 我不明白为什么我不能访问该路径的位置字段，因为它是在文档中明确规定：http://paperjs.org/reference/path/#position
这里是我的简单的代码：

paper.install(window); 
var canvas = document.getElementById("letterCanvas"); 
window.onload = function() 
{ 
    paper.setup("letterCanvas"); 

function Game(width, height) 
{ 
    this.width = width; 
    this.height = height; 
    this.tps = 60; 
    this.test = new Path.Rectangle(new Point(100,100), [50,100]); 
    this.test.strokeColor = "black"; 
} 

Game.prototype.tick = function() 
{ 
    this.test.position = this.test.position.add(5,5); 
} 

function Activity(game) 
{ 

} 

view.onFrame = function() 
{ 
    game.test.rotate(3); 
} 

var game = new Game(988,644); 
__intervalId = window.setInterval(game.tick,1000/game.tps); 
view.draw(); 
} 

Answer 1

在你的版本game.tick调用的窗口，使用此

__intervalId = window.setInterval(function() { game.tick() } ,1000/game.tps); 

Answer 2

尝试的game.tick()代替game.tick