爲什麼我的路徑位置在paper.js中未定義？

Question

我從Chrome中recieving的錯誤是： Uncaught TypeError: Cannot read property 'position' of undefined 我不明白爲什麼我不能訪問該路徑的位置字段，因爲它是在文檔中明確規定：http://paperjs.org/reference/path/#position
這裏是我的簡單的代碼：

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調用的窗口，使用此

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

Answer 2

嘗試的game.tick()代替game.tick