画个动态图：
图例：
旗帜.png
<!DOCTYPE html>
<html>
<head>
<title></title>
<style type="text/css">
#flag{
margin-top: 300px;
margin-left: 500px;
}
</style>
</head>
<body>
<div>
<canvas id='flag' width="260" height="190"></canvas>
</div>
<script type="text/javascript">
let canvas = document.getElementById('flag');
let context = canvas.getContext('2d');
context.beginPath();
context.rect(0,0,canvas.width,canvas.height);
context.closePath();
context.fillStyle = '#de2910';
context.fill();
star(context,12,30,44,50,0);
star(context, 4, 10, 92, 19, 18);
star(context, 4, 10, 111, 38, 126);
star(context, 4, 10, 111, 68, 72);
star(context, 4, 10, 92, 96, 180);
waveFlag(canvas, 30, 20, 100, 200, 0.2);
//星星
function star(ctx,r,R,x,y,rote){
context.beginPath();//开始路径
for(var i =0;i<5;i++){
//顶点
context.lineTo(Math.cos((18 + i * 72 - rote) / 180 * Math.PI) * R + x, -Math.sin((18 + i * 72 - rote) / 180 * Math.PI) * R + y);
//凹点
context.lineTo(Math.cos((54 + i * 72 - rote) / 180 * Math.PI) * r + x, -Math.sin((54 + i * 72 - rote) / 180 * Math.PI) * r + y);
}
context.closePath();
context.fillStyle = "#ffde00";
context.fill();
}
function waveFlag(canvas, wavelength, amplitude, period, shading, squeeze) {
if (!squeeze) squeeze = 0;//挤压
if (!shading) shading = 100;//阴影
if (!period) period = 200;//周期
if (!amplitude) amplitude = 10;//振幅
if (!wavelength) wavelength = canvas.width / 10;
let fps = 30;//每秒帧数
let ctx = canvas.getContext('2d');
let width = canvas.width,height = canvas.height;
let od = ctx.getImageData(0, 0, width, height).data;//获取canvas的像素数据数组
return setInterval(function() {
let id = ctx.getImageData(0, 0, width, height);
let d = id.data;
let now = (new Date) / period;
for (let y = 0; y < height; ++y) {
let lastO = 0,
shade = 0;
let sq = (y - height / 2) * squeeze;
for (let x = 0; x < width; ++x) {
let px = (y * width + x) * 4;
let pct = x / width;
let o = Math.sin(x / wavelength - now) * amplitude * pct;
let y2 = y + (o + sq * pct) << 0;
let opx = (y2 * width + x) * 4;
shade = (o - lastO) * shading;
d[px] = od[opx] + shade;
d[px + 1] = od[opx + 1] + shade;
d[px + 2] = od[opx + 2] + shade;
d[px + 3] = od[opx + 3];
lastO = o;
}
}
context.putImageData(id, 0, 0);
}, 2000 / fps);
}
</script>
</body>
</html>
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