本篇文章为大家展示了怎么在html5中利用canvas实现一个弹幕功能，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。
(function () { window.onload=function () { var video = document.getElementsByTagName("video")[0] var cav = document.getElementsByTagName("canvas")[0] //设置常量canvas的高度以及宽度 var cavWidth = 800 var cavHeight = 420 cav.width=cavWidth cav.height=cavHeight var ctx = cav.getContext("2d") //存储弹幕对象的数组 var capObjs = [] var lastItemTime var capHeight = 20 var inputEle = document.getElementsByClassName("caption-input-text")[0] var sendEle = document.getElementsByClassName("caption-sendButton")[0] var colorUl = document.getElementsByClassName("colorItems")[0] var ismoveInputEle = document.getElementsByClassName("caption-input-ismove")[0] //弹幕颜色 var colors=["#fff","#FFCCCC","#CCFFCC","#CCCCFF","#FFFFCC","#CCFFFF"] var selectedColorIndex = 0 var prevPlayTime = 0 //测试数据的数组 var testArrayCopy = [] var capobjId = 0 //弹幕在画布中高度可能值组成的数组 var topObjs = [{blank:true , value : 20 ,index:0}, {blank:true , value : 50 ,index:1}, {blank:true , value : 80 ,index:2}, {blank:true , value : 110 ,index:3}, {blank:true , value : 140 ,index:4}, {blank:true , value : 170 ,index:5}, {blank:true , value : 200 ,index:6}, {blank:true , value : 230 ,index:7}, {blank:true , value : 260 ,index:8}, {blank:true , value : 290 ,index:9}, {blank:true , value : 320 ,index:10}, {blank:true , value : 350 ,index:11}, {blank:true , value : 380 ,index:12}, {blank:true , value : 410 ,index:13}]//test data 测试数据var testArray = [{content:"ABCDEFGHIJKLMNOPQRSTUVWXYZ",time:"1",ismove:false,colorIndex:0},{content:"233333333333333",time:"2",ismove:true,colorIndex:0},{content:"干杯，哈哈哈~~~~~~",time:"2",ismove:true,colorIndex:5},{content:"干杯，哈哈哈~~~~~~",time:"2",ismove:true,colorIndex:4},{content:"干杯，哈哈哈~~~~~~",time:"2",ismove:true,colorIndex:4},{content:"干杯，哈哈哈~~~~~~",time:"2",ismove:true,colorIndex:0},{content:"干杯，哈哈哈~~~~~~",time:"2",ismove:true,colorIndex:0},{content:"233333333333333",time:"3",ismove:true,colorIndex:0},{content:"233333333333333",time:"3",ismove:true,colorIndex:0},{content:"233333333333333",time:"3",ismove:true,colorIndex:0},{content:"233333333333333",time:"3",ismove:true,colorIndex:0},{content:"233333333333333",time:"3",ismove:true,colorIndex:0},{content:"233333333333333",time:"3",ismove:true,colorIndex:0},{content:"233333333333333",time:"4",ismove:false,colorIndex:0},{content:"233333333333333",time:"5",ismove:true,colorIndex:4},{content:"233333333333333",time:"6",ismove:true,colorIndex:2},{content:"233333333333333",time:"7",ismove:true,colorIndex:2},{content:"233333333333333",time:"7",ismove:true,colorIndex:2},{content:"233333333333333",time:"7",ismove:true,colorIndex:2},{content:"233333333333333",time:"7",ismove:true,colorIndex:2},{content:"233333333333333",time:"7",ismove:true,colorIndex:2},{content:"233333333333333",time:"7",ismove:true,colorIndex:2},{content:"233333333333333",time:"8",ismove:true,colorIndex:0},{content:"233333333333333",time:"9",ismove:true,colorIndex:0},{content:"233333333333333",time:"10",ismove:true,colorIndex:0},{content:"老师说的非常好，我要好好学习了》》》》",time:"12",ismove:true,colorIndex:0},{content:"老师说的非常好，我要好好学习了》》》》",time:"13",ismove:true,colorIndex:0},{content:"老师说的非常好，我要好好学习了》》》》",time:"14",ismove:true,colorIndex:2},{content:"老师说的非常好，我要好好学习了》》》》",time:"15",ismove:false,colorIndex:0},{content:"老师说的非常好，我要好好学习了》》》》",time:"16",ismove:true,colorIndex:2},{content:"老师说的非常好，我要好好学习了》》》》",time:"17",ismove:true,colorIndex:3},{content:"老师说的非常好，我要好好学习了》》》》",time:"18",ismove:true,colorIndex:2},{content:"老师说的非常好，我要好好学习了》》》》",time:"19",ismove:true,colorIndex:0},{content:"老师说的非常好，我要好好学习了》》》》",time:"20",ismove:true,colorIndex:3},{content:"老师说的非常好，我要好好学习了》》》》",time:"21",ismove:true,colorIndex:0},{content:"老师说的非常好，我要好好学习了》》》》",time:"22",ismove:true,colorIndex:0},{content:"老铁们，小礼物走一波了，小汽车小火箭刷起来吧=========",time:"23",ismove:true,colorIndex:0},{content:"老铁们，小礼物走一波了，小汽车小火箭刷起来吧=========",time:"24",ismove:true,colorIndex:0},{content:"老铁们，小礼物走一波了，小汽车小火箭刷起来吧=========",time:"25",ismove:true,colorIndex:3},{content:"老铁们，小礼物走一波了，小汽车小火箭刷起来吧=========",time:"26",ismove:true,colorIndex:0},{content:"老铁们，小礼物走一波了，小汽车小火箭刷起来吧=========",time:"27",ismove:true,colorIndex:5},{content:"老铁们，小礼物走一波了，小汽车小火箭刷起来吧=========",time:"28",ismove:false,colorIndex:5},{content:"老铁们，小礼物走一波了，小汽车小火箭刷起来吧=========",time:"29",ismove:true,colorIndex:5},{content:"老铁们，小礼物走一波了，小汽车小火箭刷起来吧=========",time:"30",ismove:true,colorIndex:5},{content:"马上就下课了，瓦罗蓝大陆走起了～～～",time:"31",ismove:true,colorIndex:5},{content:"马上就下课了，瓦罗蓝大陆走起了～～～",time:"32",ismove:true,colorIndex:2},{content:"马上就下课了，瓦罗蓝大陆走起了～～～",time:"33",ismove:true,colorIndex:2},{content:"马上就下课了，瓦罗蓝大陆走起了～～～",time:"33",ismove:true,colorIndex:5},{content:"马上就下课了，瓦罗蓝大陆走起了～～～",time:"34",ismove:true,colorIndex:5},{content:"马上就下课了，瓦罗蓝大陆走起了～～～",time:"35",ismove:true,colorIndex:5},{content:"马上就下课了，瓦罗蓝大陆走起了～～～",time:"36",ismove:true,colorIndex:2},{content:"马上就下课了，瓦罗蓝大陆走起了～～～",time:"37",ismove:true,colorIndex:2}] //将测试数据备份 copyArray(testArray , testArrayCopy) function Caption( ismove , spe , col , text ) { this.isMove = ismove this.speed = spe this.color = col || "#ff0" this.content = text this.latestTime = 0 this.width = text.length * 20 this.id = 0 this.topIndex = 0 this.occupyPos = true this.top = 300 this.left = 0 this.setLeftValue() this.setTopValue() } Caption.prototype.setTopValue = function () { for(var i = 0 ,len = topObjs.length ; i < len ; i++){ if (topObjs[i].blank) { this.top = topObjs[i].value this.topIndex = i topObjs[i].blank = false break } } } Caption.prototype.setLeftValue = function () { if (this.isMove) { this.left = cavWidth } else { var contentLength = this.content.length var nowItemLeft = 420 - contentLength * 9 this.left = nowItemLeft } } Caption.prototype.moving = function () { if (this.isMove) { this.left-=this.speed if ( this.left + this.width < cavWidth && this.occupyPos) { this.occupyPos = false topObjs[this.topIndex].blank = true } } else{ this.latestTime += 1 if (this.latestTime > 450) { topObjs[this.topIndex].blank = true } } } Caption.prototype.setId = function () { this.id = capobjId capobjId++ } var cap1 = new Caption( false , 1 , 0 , "小礼物走一波，双击6666。。。。") capObjs.push(cap1) cap1.setId() //循环遍历数组，根据对象的属性绘制在画布上 function drawAllText () { ctx.clearRect( 0 , 0 , cavWidth , cavHeight) ctx.beginPath() for(var i=0 , len = capObjs . length ; i < len ; i++ ){ ctx.fillStyle = capObjs[i].color ctx.font = "bold 20px Courier New" ctx.fillText( capObjs[i].content , capObjs[i].left , capObjs[i].top ) ctx.closePath() capObjs[i].moving() // if (capObjs[i].left < - cavWidth ) { // capObjs.splice (i ,1) // if excute this statement , will has fault because some item in array is null // solution is : write a new function to refresh the array // } } } //更新数组，当对象已经超出范围的时候从数组删除这个对象 function refreshObjs(objs) { for (var i = objs.length - 1; i >= 0; i--) { if (objs[i].left < - cavWidth || objs[i].latestTime > 450 ) { objs.splice(i , 1) } } } //更新保存弹幕对象的数组 function updateArray () { var now = parseInt( video.currentTime ) for (var i = testArray.length - 1; i >= 0; i--) { var nowItemTime = parseInt(testArray[i].time) if ( nowItemTime == now ) { //首次写的控制高度的方式，空间利用不充分，后来改为setTopValue中的方式 // var nowItemLeft = getLeftValue(testArray[i]) // var diffTime = Math.abs(nowItemTime - lastItemTime) // if (diffTime < 6) { // capHeight += 30 // capHeight = capHeight > 400 ? 20 : capHeight // } var temcolor = colors[testArray[i].colorIndex] var temcap = new Caption ( testArray[i].ismove , 1 , temcolor , testArray[i].content ) capObjs.push(temcap) capObjs[capObjs.length - 1].setId() temcap = null testArray.splice(i,1) } } } //当用户点击send发送弹幕的回调函数 function sendCaption (argument) { var inputEleTxt = inputEle.value var now = parseInt( video.currentTime ) var inputIsmoveValue = ismoveInputEle.checked var temObj = {content:inputEleTxt,time:now,ismove:inputIsmoveValue,colorIndex:selectedColorIndex} testArray.push(temObj) inputEle.value = "" } // function getLeftValue (obj) { // if (obj.ismove) { // return 0 // } // else { // var contentLength = obj.content.length // var nowItemLeft = 420 - contentLength * 9 // return nowItemLeft // } // } //重新启动canvas，用在人为导致进度条时间的改变 function reinitCav (argument) { // testArray = testArrayCopy copyArray(testArrayCopy , testArray) capObjs = [] capHeight = 0 clearInterval(canvasTimer) canvasTimer = null initCanvas() } var canvasTimer = null //初始化canvas，用在开始播放时 function initCanvas () { if (canvasTimer == null ) { canvasTimer = setInterval(function (argument) { drawAllText() updateArray() refreshObjs(capObjs) },10) } }//end function initCanvas //复制数组 function copyArray (arr1 , arr2) { for (var i =0 , len=arr1.length ; i < len ; i++) { arr2[i] = arr1[i] } } //color select event 用户发送弹幕的颜色控制代码 colorUl.addEventListener("click", function( e ){ var prevSelectItemId = "" switch (selectedColorIndex) { case 0: prevSelectItemId = "colorItemFrist" break; case 1: prevSelectItemId = "colorItemSecond" break; case 2: prevSelectItemId = "colorItemThrid" break; case 3: prevSelectItemId = "colorItemFourth" break; case 4: prevSelectItemId = "colorItemFifth" break; case 5: prevSelectItemId = "colorItemSixth" break; default: // statements_def break; } var prevSelectItem = document.getElementById(prevSelectItemId) prevSelectItem.className = "" var eventTarget = e.target eventTarget.className = "selectedColor" var eveTarId = eventTarget.id.substring(9) switch (eveTarId) { case "Frist": selectedColorIndex = 0 break; case "Second": selectedColorIndex = 1 break; case "Thrid": selectedColorIndex = 2 break; case "Fourth": selectedColorIndex = 3 break; case "Fifth": selectedColorIndex = 4 break; case "Sixth": selectedColorIndex = 5 break; default: // statements_def break; } }, false) video.addEventListener("playing" , function () { initCanvas() }) //进度条改变执行代码 video.addEventListener("timeupdate", function () { var nowPlayTime = video.currentTime var diffTime = Math.abs(nowPlayTime - prevPlayTime) prevPlayTime = nowPlayTime if (diffTime > 1) { reinitCav() } }, false) //视频暂停执行代码 video.addEventListener("pause" , function () { clearInterval(canvasTimer) canvasTimer = null }) //点击send的监听事件 sendEle.addEventListener("click" , sendCaption) //input的回车监听事件 inputEle.addEventListener("keydown", function(e) { var keynum = 0 keynum = window.event ? e.keyCode : e.which if (keynum == 13) { sendCaption() } }) var aaaa = function() { alert(1) } aaaa() // function b(aaaa){ // return aaaa() // } // b() }//end})()上述内容就是怎么在html5中利用canvas实现一个弹幕功能，你们学到知识或技能了吗？如果还想学到更多技能或者丰富自己的知识储备，欢迎关注编程网行业资讯频道。
