思路：使用Math.random()函数绘制是个不同位置，大小，颜色的圆形，然后设置定时器，前一个状态用一个与画布相同颜色的背景图片进行覆盖，改变圆形的位置，每次改变都是在这张空白的背景图片上面重新进行重新绘制的过程
源码：
<!doctype html>
<html>
<head>
<title>test</title>
<meta charset="UTF-8">
</head>
<body>
<canvas id="canvas" Style="border:solid black thin" width="600px" height="500px"></canvas>
<script>
var canvas = document.getElementById("canvas");
var context = canvas.getContext('2d');
const WIDTH = canvas.width;
const HEIGHT = canvas.height;
var img = new Image();
img.src = "white.png";
var rangeX=[];//用来存储生成的十组x坐标//这里的气泡属性用一个对象来进行封装，再将对象存储在数组中更恰当
var rangeY=[];//用来存储生成的十组y坐标
var rangeR=[];//用来存储生成的十足气泡的半径
var red=[];//用来存储红色的数值
var green=[];//用来存储绿色的数值
var blue=[];//用来存储蓝色的数值
for( var i=0;i<20;i++){//事先生成十组气泡的x坐标和半径
var r = Math.random() * 50;
var x = WIDTH * Math.random();
if (x < r) {
x = r;
}
if (x > WIDTH - r) {
x = WIDTH - r;
}
var y = WIDTH * Math.random();
if (y < r) {
y = r;
}
if (y > WIDTH - r) {
y = WIDTH - r;
}
rangeX[i]=x;
rangeR[i]=r;
rangeY[i]=y;
red[i]=Math.random()*255;
green[i]=Math.random()*255;
blue[i]=Math.random()*255;
}
var algha=0.3;
var tag=1;//设一个标记，标记气泡是在往下走还是往上走，往下是1，往上是0
var setinterval = setInterval(function () {
context.beginPath();
context.drawImage(img, 0, 0);
for (var i = 0; i < 20; i++) {
var randomX=Math.random()*3;
var randomY=Math.random()*3;
if(tag===1){
if (rangeX[i]+rangeR[i] >= WIDTH && rangeY[i]+rangeR[i] >= HEIGHT) {
tag=0;
}
context.beginPath();
rangeX[i]=rangeX[i]+randomX;
rangeY[i]=rangeY[i]+randomY;
context.arc(rangeX[i], rangeY[i], rangeR[i], 0, Math.PI * 2, false);
context.fillStyle = "rgba("+red[i]+","+green[i]+","+blue[i]+","+algha+")";
context.fill();
} else{
if (rangeX[i]-rangeR[i] <=0 && rangeY[i]-rangeR[i] <=0) {
tag=1;
}
context.beginPath();
rangeX[i]=rangeX[i]-randomX;
rangeY[i]=rangeY[i]-randomY;
context.arc(rangeX[i], rangeY[i], rangeR[i], 0, Math.PI * 2, false);
context.fillStyle = "rgba("+red[i]+","+green[i]+","+blue[i]+","+algha+")";
context.fill();
}
}
context.closePath();
}, 100);
</script>
</body>
</html>
效果图：
缺陷：
气泡移动的路径算法处理的不是很恰当