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 thepage 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
(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 < 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
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Drag event editor implements drag and drop upload image effect
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