canvas实现拖动页面时显示窗口视频

 1 <style>
 2         html{height:2000px;}
 3         div{width: 500px;margin:40px auto;}
 4     </style>
 5 
 6 ------------------------------------------------------------------------
 7 
 8 <div>
 9     <video id="v" controls="controls" autoplay="autoplay" src="a.mp4" width="500" height="300"></video>
10 </div>
11 
12 ------------------------------------------------------------------------
13 
14 function $(i){return document.getElementById(i)}
15     var v = $("v");
16     function fixScrollEvent(el,fn,context){
17         var type = "mousewheel";
18         context = context || window;
19         try{
20             document.createEvent("MouseScrollEvents");
21             type = "DOMMouseScroll";
22         }catch(e){}
23         if(type == "mousewheel"){
24             el.onmousewheel = function(e){
25                 e = e || window.event;
26                 if(window.opera && window.opera.version()<10){
27                     e.delta = -e.wheelDelta / 30;
28                 }else{
29                     e.delta = e.wheelDelta / 30;
30                 }
31                 fn.call(context,e);
32             }
33         }else{
34             el.addEventListener("DOMMouseScroll",function(e){
35                 e.delta = -e.detail;
36                 fn.call(context,e);
37             },false)
38         }
39     }
40 
41     fixScrollEvent(window,function(e){
42         var dh,cp;
43         var c, d,graphic;
44         var imageData;
45         //视口宽度和高度
46         var vpWidth = window.innerWidth || document.documentElement.clientWidth
47                 || document.body.clientWidth;
48         var vpHeight = window.innerHeight || document.documentElement.clientHeight
49                 || document.body.clientHeight;
50         cp = v.getBoundingClientRect();
51         dh = cp.top + v.scrollTop + v.clientHeight;
52 
53         c = $("miniVideo");
54         if(dh < document.documentElement.scrollTop){
55             if(c){
56                 c.setAttribute("data-flag",1);
57                 c.style.display = "";
58             }else{
59                 c = document.createElement("canvas");
60                 c.id = "miniVideo";
61                 // Drag 拖动插件必须要确定top和left值，不能使用right和bottom代替。
62                 c.style.cssText = "width:300px;height:200px;background:black;position:fixed;" +
63                         "left:"+(vpWidth - 30 - 300)+"px;top:"+(vpHeight - 20 - 200)+"px;";
64                 c.setAttribute("data-flag",1);
65                 if(c.innerText !== undefined){
66                     c.innerText = "Your Browser can not support Canvas!";
67                 }else{
68                     c.textContent = "Your Browser can not support Canvas!";
69                 }
70                 document.body.appendChild(c);
71                 new Drag(c)
72 
73             }
74             requestAnimationFrame(function recurse(){
75                 graphic = c.getContext("2d");
76                 graphic.drawImage(v,0,0, c.width, c.height);
77                 if(c.getAttribute("data-flag")){
78                     requestAnimationFrame(recurse);
79                 }
80             })
81         }else{
82             if(c){
83                 //设置空字符串，之前犯了个错误，在html property保存的始终是字符串。
84                 c.setAttribute("data-flag","");
85                 c.style.display = "none";
86             }
87         }
88     })