canvas 波浪效果

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>