源代码如下：

1.  
2.       
3.         "Content-Type" content="text/html; charset=utf-8">  
4.           
5.    
6.         "text/css">  
7.             body{  
8.                 margin:0px;  
9.             }  
10.           
11.    
12.         "text/javascript">  
13.    
14.             var imageCanvas;  
15.             var maskCanvas;  
16.             var imageContext;  
17.             var maskContext;  
18.             var frameCount=0;  
19.             var nextFrames=0;  
20.             var maskX=225;  
21.             var maskY=160;  
22.             var maskSpeedX=0;  
23.             var maskSpeedY=0;  
24.             var MASK_R=75;  
25.             var CANVAS_WIDTH=500;  
26.             var CANVAS_HEIGHT=320;  
27.    
28.             function pageInit(){  
29.                 imageCanvas=document.createElement_x("canvas");  
30.                 imageCanvas.width=CANVAS_WIDTH;  
31.                 imageCanvas.height=CANVAS_HEIGHT;  
32.                 document.body.appendChild(imageCanvas);  
33.                 imageCanvas.style.position="absolute";  
34.                 imageContext=imageCanvas.getContext("2d");  
35.                 var img=new Image();  
36.                 img.onload=function(){  
37.                     imageContext.drawImage(img,0,0);  
38.                 }  
39.                 img.src="/uploads/allimg/120621/1_120621112049_1.jpg";  
40.    
41.                 maskCanvas=document.createElement_x("canvas");  
42.                 maskCanvas.width=CANVAS_WIDTH;  
43.                 maskCanvas.height=CANVAS_HEIGHT;  
44.                 document.body.appendChild(maskCanvas);  
45.                 maskCanvas.style.position="absolute";  
46.                 maskContext=maskCanvas.getContext("2d");  
47.    
48.                 resetSpeed();  
49.                 setInterval(moveMask,20);  
50.             }  
51.    
52.             function resetSpeed(){  
53.                 maskSpeedX=Math.random()*10-5;  
54.                 maskSpeedY=Math.random()*10-5;  
55.    
56.                 resetNextFrames();  
57.             }  
58.    
59.             function resetNextFrames(){  
60.                 nextFrames=Math.random()*125+25;  
61.             }  
62.    
63.             function moveMask(){  
64.    
65.                 maskContext.clearRect(0,0,CANVAS_WIDTH,CANVAS_HEIGHT);  
66.                 maskContext.globalCompositeOperation="source-over";  
67.                 maskContext.fillRect(0,0,CANVAS_WIDTH,CANVAS_HEIGHT);  
68.                 maskContext.globalCompositeOperation="destination-out";  
69.                 maskContext.beginPath();  
70.                 maskContext.arc(maskX,maskY,MASK_R,0,Math.PI*2,true);  
71.                 maskContext.fill();  
72.    
73.                 maskX+=maskSpeedX;  
74.                 maskY+=maskSpeedY;  
75.    
76.                 if(maskX>=CANVAS_WIDTH-MASK_R){  
77.                     maskSpeedX=-Math.abs(maskSpeedX);  
78.                 }  
79.                 if(maskX<=MASK_R){  
80.                     maskSpeedX=Math.abs(maskSpeedX);  
81.                 }  
82.                 if(maskY>=CANVAS_HEIGHT-MASK_R){  
83.                     maskSpeedY=-Math.abs(maskSpeedY);  
84.                 }  
85.                 if(maskY<=MASK_R){  
86.                     maskSpeedY=Math.abs(maskSpeedY);  
87.                 }  
88.    
89.                 frameCount++;  
90.                 if(frameCount>nextFrames){  
91.                     frameCount=0;  
92.                     resetSpeed();  
93.                 }  
94.             }  
95.           
96.       
97.     "pageInit();">  
98.    
99.       
100.  
101.