基于canvas的三次贝塞尔曲线(bezierCurveTo)

<canvas id="myCanvas"></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>