场景设置：

#canvas1{

position:absolute;

bottom:0;

left:0;

z-index:1;

}

#canvas2{

position:absolute;

bottom:0;

left:0;

z-index:0;

}

画布获取：

can1=document.getElementById("canvas1");

ctx1=can1.getContext('2d');/* 绘制 2d 场景 */

大鱼设置：

this.x =canWidth * 0.5;

this.y =canHeight * 0.5;

ctx1.drawImage(this.bigEye, -this.bigEye * 0.5, -this.bigEye * 0.5);

ctx1.drawImage(this.bigBody, -this.bigBody * 0.5, -this.bigBody * 0.5);

ctx1.drawImage(this.bigTail, -this.bigTail * 0.5 + 30, -this.bigTail * 0.5);