这是CSS代码：

body{    padding: 20px;}
.all_bg {    
display: inline-block;    
width: 800px;    
height: 600px;    
position: relative;
}
.all_bg .allCanvas {    
position: relative;    
width: 800px;    
height: 600px;    
margin: 0;
}
#canvas1 {    
position: absolute;    
top: 0;    
left: 0;    
z-index: 1;
}
#canvas2 {    
position: absolute;    
top: 0;    
left: 0;    
z-index: 0;
}

大鱼的JS代码：

var bigFishObj = function(){    
this.x;    
this.y;    
this.bigEye = new Image();    
this.bigBody = new Image();    
this.bigTail = new Image();
}
bigFishObj.prototype.init = function(){    
this.x = canWidth * 0.5;    
this.y = canHeight * 0.5;    
this.bigEye.src = "./src/bigEye0.png";    
this.bigBody.src = "./src/bigSwim0.png";    
this.bigTail.src = "./src/bigTail0.png";
}
bigFishObj.prototype.drawImage = function(){    
ctx1.save();    
ctx1.drawImage(this.bigEye, this.x, this.y);    
ctx1.drawImage(this.bigBody, this.x, this.y);    
ctx1.drawImage(this.bigTail, this.x, this.y);    
ctx1.restore();
}

而且我的canvas1和canvas2不是重叠的，但是看老师演示两个canvas是重叠在一起的