text: /* 二维向量 */
  game.Vector2 = function(x,y){
  	this.x = x || 0;
  	this.y = y || 0;
  }
  
  game.Vector2.prototype = {
  	copy:function(){return new game.Vector2(this.x,this.y)},
  	iadd:function(v){this.x+=v.x;this.y+=v.y;return this;s},
  	muls:function(n){return new game.Vector2(this.x*n,this.y*n)}
  }