大鱼一直不显示

 //大鱼var momObj=function(){
 this.x;
 this.y;
 this.bigEye=new Image();
 this.bigBody=new Image();
 this.bigTail=new Image();
 }
 momObj.prototype.init=function(){
 	this.x=canWidth*0.5;	
 	this.y=canHeight*0.5;
 	this.bigEye.src="img/bigEye0.png";
 	this.bigBody.src="img/bigSwim0.png";	
 	this.bigTail.src="img/bigTail0.png";
 	}
 momObj.prototype.draw=function(){
 	ctx1.save();	
 	ctx1.translate(this.x,this.y);	
 	ctx1.drawImage(this.bigEye,-this.bigEye.width*0.5,-this.bigEye.height*0.5);	
 	ctx1.drawImage(this.bigBody,-this.bigBody.width*0.5,-this.bigBody.height*0.5);	
 	ctx1.drawImage(this.bigTail,-this.bigTail.width*0.5+30,-this.bigTail.height*0.5);	
 	ctx1.restore();
 	}