Use canvas to achieve barrage effects in videos

This time I will bring you the use of canvas to achieve the barrage effect in videos. What are the precautions for using canvas to achieve the barrage effect of videos? The following is a practical case, let’s take a look.

Recently, I have started to develop a barrage video website, and realized the barrage function through canvas in html5.

So don’t talk nonsense, talk about your ideas first and then write the code.

Idea: From the

page layout point of view, it is to cover a canvas on the video window generated by the video tag, which can be achieved by using absolute positioning. The most important thing is that js controls the display of barrages on the canvas. Each barrage is packaged into an object. The properties contained in the object include the time when the barrage should appear, the color of the barrage, whether the barrage is moving and the barrage. text. The methods owned by the barrage object include: setting the horizontal and vertical coordinates of the barrage, and the movement function of the barrage. The principle of implementation is to monitor the event of the video starting to play, and generate a timer when the video starts playing. The timer traverses the cyclic barrage object array at every other time and draws the barrage at the appropriate position on the canvas according to the properties of the object. , in addition to the code for drawing the barrage, the timer also contains the code for updating the barrage array.

The picture below is a screenshot of the barrage effect

Then start the code directly:

(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)
        /*弹幕对象的构造函数，参数分别是：1.ismove：弹幕是否是移动的弹幕,2.spe:弹幕的移动速度，3.col：弹幕的颜色，4.text：弹幕的文本*/
        /*原型链方法 setTopValue设置纵坐标，setLeftValue设置横坐标，moving完成坐标的改变，setId完成id值的设置*/
        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  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 = 0; i--) {
                if (objs[i].left  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  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  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
})()

I believe you have mastered it after reading the case in this article For more exciting methods, please pay attention to other related articles on the php Chinese website!

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The above is the detailed content of Use canvas to achieve barrage effects in videos. For more information, please follow other related articles on the PHP Chinese website!