为什么我的大鱼没有显示出来

//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();

}