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这里展示白色半透明气泡如下图：实际是动态
思路：HTML里只需要一个CANVAS元素，Javascript里操作canvas
1、给canvas里绘制背景图片
2、在绘制半径为0-10px的圆形，x坐标屏幕水平随机，y所标竖直大于屏幕高度。
圆形背景色可以是随机。那就是各种色彩了！
利用计时器控制y--
<!doctype html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="Generator" content="EditPlus®"> <meta name="Author" content=""> <meta name="Keywords" content=""> <meta name="Description" content=""> <title>5多个小球往上运动</title> <style> </style> </head> <body> <div id="d1"> <canvas id="canvas"></canvas> </div> </body> </html>
<script>
var canvas=document.getElementById("canvas");
var context=canvas.getContext("2d");
canvas.width=window.innerWidth;
canvas.height=window.innerHeight;
function Circle(){
this.x=Math.random()*canvas.width;
this.y=canvas.height;
this.r=Math.random()*10;
//绘制圆形
this.paint=function(){
context.beginPath();
context.arc(this.x,this.y,this.r,0,Math.PI*2);
context.fillStyle="white";
context.globalAlpha = 0.5;
context.fill();
}
//控制圆形移动
this.step=function(){
this.y--;
}
}
var circles=[];
function createCircles(){
var circle=new Circle();//??????
circles[circles.length]=circle;
}
function paintCircles(){
for(var i=0;i<circles.length;i++){
circles[i].paint();
}
}
function stepCircles(){
for(var i=0;i<circles.length;i++){
circles[i].step();
}
}
var myimg=new Image();
myimg.src="images/demo-1.png";
var timer="";
setInterval(function(){
context.drawImage(myimg,0,0);
timer++;
if(timer%20==0){
createCircles();
}
paintCircles();
stepCircles();
},10);
</script>
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原文地址：http://www.cnblogs.com/-walker/p/4985879.html
