h5怎么通過(guò)canvas來(lái)完成滾動(dòng)彈幕技巧

最近在著手開(kāi)發(fā)彈幕視頻網(wǎng)站，通過(guò)html5中的canvas實(shí)現(xiàn)了彈幕的功能。

那么閑言碎語(yǔ)不要講，先說(shuō)思路后上代碼。

思路：從頁(yè)面布局上來(lái)說(shuō)就是將一塊畫(huà)布覆蓋在了video標(biāo)簽產(chǎn)生的視頻窗口之上，使用絕對(duì)定位就能實(shí)現(xiàn)了。最重要的就是js控制畫(huà)布上彈幕的顯示了，每一個(gè)彈幕都包裝成一個(gè)對(duì)象，對(duì)象包含的屬性有彈幕應(yīng)該出現(xiàn)的時(shí)間，彈幕的顏色，彈幕是否是移動(dòng)的以及彈幕的文本。彈幕對(duì)象擁有方法包含：設(shè)置彈幕的橫縱坐標(biāo)，彈幕的移動(dòng)函數(shù)。實(shí)現(xiàn)的原理，在監(jiān)聽(tīng)視頻開(kāi)始播放的事件，在視頻開(kāi)始播放時(shí)生成一個(gè)定時(shí)器，定時(shí)器每隔一個(gè)時(shí)間去遍歷循環(huán)彈幕對(duì)象數(shù)組并根據(jù)對(duì)象的屬性在畫(huà)布的適當(dāng)位置上繪制出彈幕，計(jì)時(shí)器中除了繪制彈幕的代碼還有執(zhí)行更新彈幕數(shù)組的代碼。

那么下面開(kāi)始直接上代碼：

(function () {
    window.onload=function () {
        var video = document.getElementsByTagName("video")[0]
        var cav = document.getElementsByTagName("canvas")[0]
        //設(shè)置常量canvas的高度以及寬度
        var cavWidth = 800
        var cavHeight = 420
        cav.width=cavWidth
        cav.height=cavHeight
        var ctx = cav.getContext("2d")
        //存儲(chǔ)彈幕對(duì)象的數(shù)組
        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]
        //彈幕顏色
        var colors=["#fff","#FFCCCC","#CCFFCC","#CCCCFF","#FFFFCC","#CCFFFF"]
        var selectedColorIndex = 0
        var prevPlayTime = 0
        //測(cè)試數(shù)據(jù)的數(shù)組
        var testArrayCopy = []
        var capobjId = 0
        //彈幕在畫(huà)布中高度可能值組成的數(shù)組
        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 測(cè)試數(shù)據(jù)
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:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"12",ismove:true,colorIndex:0},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"13",ismove:true,colorIndex:0},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"14",ismove:true,colorIndex:2},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"15",ismove:false,colorIndex:0},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"16",ismove:true,colorIndex:2},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"17",ismove:true,colorIndex:3},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"18",ismove:true,colorIndex:2},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"19",ismove:true,colorIndex:0},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"20",ismove:true,colorIndex:3},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"21",ismove:true,colorIndex:0},
{content:"老師說(shuō)的非常好，我要好好學(xué)習(xí)了》》》》",time:"22",ismove:true,colorIndex:0},
{content:"老鐵們，小禮物走一波了，小汽車(chē)小火箭刷起來(lái)吧=========",time:"23",ismove:true,colorIndex:0},
{content:"老鐵們，小禮物走一波了，小汽車(chē)小火箭刷起來(lái)吧=========",time:"24",ismove:true,colorIndex:0},
{content:"老鐵們，小禮物走一波了，小汽車(chē)小火箭刷起來(lái)吧=========",time:"25",ismove:true,colorIndex:3},
{content:"老鐵們，小禮物走一波了，小汽車(chē)小火箭刷起來(lái)吧=========",time:"26",ismove:true,colorIndex:0},
{content:"老鐵們，小禮物走一波了，小汽車(chē)小火箭刷起來(lái)吧=========",time:"27",ismove:true,colorIndex:5},
{content:"老鐵們，小禮物走一波了，小汽車(chē)小火箭刷起來(lái)吧=========",time:"28",ismove:false,colorIndex:5},
{content:"老鐵們，小禮物走一波了，小汽車(chē)小火箭刷起來(lái)吧=========",time:"29",ismove:true,colorIndex:5},
{content:"老鐵們，小禮物走一波了，小汽車(chē)小火箭刷起來(lái)吧=========",time:"30",ismove:true,colorIndex:5},
{content:"馬上就下課了，瓦羅藍(lán)大陸走起了～～～",time:"31",ismove:true,colorIndex:5},
{content:"馬上就下課了，瓦羅藍(lán)大陸走起了～～～",time:"32",ismove:true,colorIndex:2},
{content:"馬上就下課了，瓦羅藍(lán)大陸走起了～～～",time:"33",ismove:true,colorIndex:2},
{content:"馬上就下課了，瓦羅藍(lán)大陸走起了～～～",time:"33",ismove:true,colorIndex:5},
{content:"馬上就下課了，瓦羅藍(lán)大陸走起了～～～",time:"34",ismove:true,colorIndex:5},
{content:"馬上就下課了，瓦羅藍(lán)大陸走起了～～～",time:"35",ismove:true,colorIndex:5},
{content:"馬上就下課了，瓦羅藍(lán)大陸走起了～～～",time:"36",ismove:true,colorIndex:2},
{content:"馬上就下課了，瓦羅藍(lán)大陸走起了～～～",time:"37",ismove:true,colorIndex:2}]
        //將測(cè)試數(shù)據(jù)備份
        copyArray(testArray , testArrayCopy)
        /*彈幕對(duì)象的構(gòu)造函數(shù)，參數(shù)分別是：1.ismove：彈幕是否是移動(dòng)的彈幕,2.spe:彈幕的移動(dòng)速度，3.col：彈幕的顏色，4.text：彈幕的文本*/
        /*原型鏈方法 setTopValue設(shè)置縱坐標(biāo)，setLeftValue設(shè)置橫坐標(biāo)，moving完成坐標(biāo)的改變，setId完成id值的設(shè)置*/
        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 , "小禮物走一波，雙擊6666。。。。")
        capObjs.push(cap1)
        cap1.setId()
         
        //循環(huán)遍歷數(shù)組，根據(jù)對(duì)象的屬性繪制在畫(huà)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  
                // }
            }
        }
         
        //更新數(shù)組，當(dāng)對(duì)象已經(jīng)超出范圍的時(shí)候從數(shù)組刪除這個(gè)對(duì)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)
                }
 
            }
        }
         
        //更新保存彈幕對(duì)象的數(shù)組
        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 ) {
                    //首次寫(xiě)的控制高度的方式，空間利用不充分，后來(lái)改為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)
                }
            }
        }
         
        //當(dāng)用戶點(diǎn)擊send發(fā)送彈幕的回調(diào)函數(shù)
        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
        //     }
        // }
         
        //重新啟動(dòng)canvas，用在人為導(dǎo)致進(jìn)度條時(shí)間的改變
        function reinitCav (argument) {
            // testArray = testArrayCopy
            copyArray(testArrayCopy , testArray)
            capObjs = []
            capHeight = 0
            clearInterval(canvasTimer)
            canvasTimer = null
            initCanvas()
        }
 
        var canvasTimer = null
         
        //初始化canvas，用在開(kāi)始播放時(shí)
         function initCanvas () {
             if (canvasTimer == null ) {
                canvasTimer = setInterval(function (argument) {
                    drawAllText()
                    updateArray()
                    refreshObjs(capObjs)
                },10)
             }
             
        }//end function initCanvas
         
        //復(fù)制數(shù)組
        function copyArray (arr1 , arr2) {
            for (var i =0 , len=arr1.length ; i < len ; i++) {
                    arr2[i] = arr1[i]
                }   
        }
 
        //color select event 用戶發(fā)送彈幕的顏色控制代碼
        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()
        })
         
        //進(jìn)度條改變執(zhí)行代碼
        video.addEventListener("timeupdate", function  () {
            var nowPlayTime = video.currentTime
            var diffTime = Math.abs(nowPlayTime - prevPlayTime)
            prevPlayTime = nowPlayTime
            if (diffTime > 1) {
                reinitCav()
            }
        }, false)
         
        //視頻暫停執(zhí)行代碼
        video.addEventListener("pause" , function () {
            clearInterval(canvasTimer)
            canvasTimer = null
        })
         
        //點(diǎn)擊send的監(jiān)聽(tīng)事件
        sendEle.addEventListener("click" , sendCaption)
         
        //input的回車(chē)監(jiān)聽(tīng)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
})()

相信看了這些案例你已經(jīng)掌握了方法，更多精彩請(qǐng)關(guān)注php中文網(wǎng)其它相關(guān)文章！

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以上就是h5怎樣通過(guò)canvas來(lái)實(shí)現(xiàn)滾動(dòng)彈幕功能的詳細(xì)內(nèi)容，更多請(qǐng)關(guān)注php中文網(wǎng)其它相關(guān)文章！