canvas知识
绘制文字
let canvas = document.getelementbyid('canvas');let ctx = canvas.getcontext('2d');ctx.font = '20px microsoft yahei'; //字体、大小ctx.fillstyle = '#000000'; //字体颜色ctx.filltext('canvas 绘制文字', 100, 100); //文本，字体x,y坐标
文本宽度
ctx.measuretext('文本宽度').width
清除绘制内容
ctx.clearrect(0, 0, width, height);
实现步骤
1、创建canvas元素利用绝对定位覆盖在视频上
2、创建barrage类，添加的弹幕缓存到弹幕列表中，并记录相应弹幕信息
3、绘制弹幕文本，用文本偏移量控制移动速度
4、计算当文本超出画布时移出弹幕列表
代码
//html<div style="position:relative;width:500px;height:400px;text-align:center;"> <video controls="controls" autoplay="autoplay" style="width:100%;height:100%;"> <source src="http://www.w3school.com.cn/i/movie.ogg" type="video/ogg" /> <source src="http://www.w3school.com.cn/i/movie.mp4" type="video/mp4" /> your browser does not support the video tag. </video> <canvas id="canvas" width="500" height="400" style="position:absolute;top:0;left:0;"> 您的浏览器不支持canvas标签。 </canvas> </div>//js(function () { class barrage { constructor(canvas) { this.canvas = document.getelementbyid(canvas); let rect = this.canvas.getboundingclientrect(); this.w = rect.right - rect.left; this.h = rect.bottom - rect.top; this.ctx = this.canvas.getcontext('2d'); this.ctx.font = '20px microsoft yahei'; this.barragelist = []; } //添加弹幕列表 shoot(value) { let top = this.gettop(); let color = this.getcolor(); let offset = this.getoffset(); let width = math.ceil(this.ctx.measuretext(value).width); let barrage = { value: value, top: top, left: this.w, color: color, offset: offset, width: width } this.barragelist.push(barrage); } //开始绘制 draw() { if (this.barragelist.length) { this.ctx.clearrect(0, 0, this.w, this.h); for (let i = 0; i < this.barragelist.length; i++) { let b = this.barragelist[i]; if (b.left + b.width <= 0) { this.barragelist.splice(i, 1); i--; continue; } b.left -= b.offset; this.drawtext(b); } } requestanimationframe(this.draw.bind(this)); } //绘制文字 drawtext(barrage) { this.ctx.fillstyle = barrage.color; this.ctx.filltext(barrage.value, barrage.left, barrage.top); } //获取随机颜色 getcolor() { return '#' + math.floor(math.random() * 0xffffff).tostring(16); } //获取随机top gettop() { //canvas绘制文字x,y坐标是按文字左下角计算，预留30px return math.floor(math.random() * (this.h - 30)) + 30; } //获取偏移量 getoffset() { return +(math.random() * 4).tofixed(1) + 1; } } let barrage = new barrage('canvas'); barrage.draw(); const textlist = ['弹幕', '666', '233333333', 'javascript', 'html', 'css', '前端框架', 'vue', 'react', 'angular','测试弹幕效果' ]; textlist.foreach((t) => { barrage.shoot(t); }) })();
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以上就是用h5的canvas做出弹幕效果的详细内容。