Canvas应用：下雨效果。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Canvas：下雨效果</title>
<style>
* {
margin: 0;
padding: 0;
}
canvas {
vertical-align: middle;
background: #000;
}
</style>
</head>
<body>
<canvas id="myCanvas"></canvas>
<script>
// 创建画布
let myCanvas = document.getElementById('myCanvas')
let ctx = myCanvas.getContext('2d')
// 自适应窗口
let width = myCanvas.width = window.innerWidth
let height = myCanvas.height = window.innerHeight
window.addEventListener('resize', () => {
width = myCanvas.width = window.innerWidth
height = myCanvas.height = window.innerHeight
})
// 绘制雨滴
let raindropArr = []
function Raindrop(x, y, w, h, l, r, dr, maxR, a, va) {
this.x = rand(0, window.innerWidth) // 雨滴的x轴
this.y = y || 0 // 雨滴的y轴
this.dy = rand(2, 4) // 雨滴的加速度
this.w = w || 2 // 雨滴的宽度
this.h = h || 10 // 雨滴的高度
this.l = rand(0.8 * height, 0.9 * height) // 雨滴的下落高度
this.r = r || 1 // 波纹半径
this.dr = dr || 1 // 波纹增加半径
this.maxR = maxR || 50 // 波纹最大半径
this.a = a || 1 // 波纹透明度
this.va = 0.96 // 波纹透明度系数
}
Raindrop.prototype = {
draw: function (index) { // 绘制雨滴
if (this.y > this.l) {
ctx.beginPath()
ctx.arc(this.x, this.y, this.r, 0, Math.PI * 2)
ctx.strokeStyle = `rgba(0,191,255,${this.a})`
ctx.stroke()
} else {
ctx.fillStyle = 'skyBlue'
ctx.fillRect(this.x, this.y, this.w, this.h)
}
this.update(index)
},
update: function (index) { // 更新雨滴坐标 运动起来
if (this.y > this.l) {
if (this.a > 0.03) {
this.r += this.dr
if (this.r > this.maxR) {
this.a *= this.va
}
} else {
this.a = 0
raindropArr.splice(index, 1)
}
} else {
this.y += this.dy
}
}
}
function rand(min, max) {
return Math.random() * (max - min) + min
}
setInterval(() => {
let raindrop = new Raindrop()
raindropArr.push(raindrop)
}, 100)
setInterval(() => {
ctx.fillStyle = 'rgba(0, 0, 0, 0.1)'
ctx.fillRect(0, 0, myCanvas.width, myCanvas.height)
for (let i = 0; i < raindropArr.length; i++) {
raindropArr[i].draw(i)
}
}, 30)
</script>
</body>
</html>
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