canvas波浪效果的实现代码

<canvas></canvas><script>    var WAVE_HEIGHT = 200 //波浪变化高度    var SCALE = 0.5 // 绘制速率    var CYCLE = 360 / SCALE    var TIME = 0    function initCanvas() {        var c = document.getElementById("myCanvas")        var width = window.screen.width        var height = window.screen.height        var ctx = c.getContext("2d")        c.width = width        c.height = height        // start        window.requestAnimationFrame(function() {            draw(ctx, width, height)        })    }    function draw(ctx, width, height) {        ctx.clearRect(0, 0, width, height)        TIME = (TIME + 1) % CYCLE        var angle = SCALE * TIME // 当前正弦角度        var dAngle = 60 // 两个波峰相差的角度        ctx.beginPath()        ctx.moveTo(0, height * 0.5 + distance(WAVE_HEIGHT, angle, 0))        ctx.bezierCurveTo(            width * 0.4,            height * 0.5 + distance(WAVE_HEIGHT, angle, dAngle),            width * 0.6,            height * 0.5 + distance(WAVE_HEIGHT, angle, 2 * dAngle),            width,            height * 0.5 + distance(WAVE_HEIGHT, angle, 3 * dAngle)        )        ctx.strokeStyle = "#ff0000"        ctx.stroke()        ctx.beginPath()        ctx.moveTo(0, height * 0.5 + distance(WAVE_HEIGHT, angle, -30))        ctx.bezierCurveTo(            width * 0.3,            height * 0.5 + distance(WAVE_HEIGHT, angle, dAngle - 30),            width * 0.7,            height * 0.5 + distance(WAVE_HEIGHT, angle, 2 * dAngle - 30),            width,            height * 0.5 + distance(WAVE_HEIGHT, angle, 3 * dAngle - 30)        )        ctx.strokeStyle = "#0000ff"        ctx.stroke()        function distance(height, currAngle, diffAngle) {            return height * Math.cos((((currAngle - diffAngle) % 360) * Math.PI) / 180)        }        // animate        window.requestAnimationFrame(function() {            draw(ctx, width, height)        })    }    initCanvas()</script>