用H5的canvas做出弹幕效果

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

ctx.measureText('文本宽度').width

ctx.clearRect(0, 0, width, height);

//html<div>
    <video>
        <source></source>
        <source></source> 
        Your browser does not support the video tag.
    </video>
    <canvas>
        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  {
        barrage.shoot(t);
    })
})();