Html5在移动设备上表现抢眼，几乎所有稍微高端一点的设备（乔帮主的iPad，iPhone和Andriod的平板手机等）的浏览器都支持Html5。而且据我个人的测试这些支持html5的设备对canvas标签的支持是相当的好。
大家都知道web2.0以来大量的使用ajax，loading的小图标也有很多很多种，甚至还有专门提供loading图片的网站。所以我就想能不能让html5解决一下这个以前用gif文件解决的问题。没想到非常的简单，只用了不到一小时的时间就搞定了两个，而且这样做出来的loading图标是可定制的，既可以定制颜色，也可以定制大小等属性。
看看效果吧：
http://f200-8.bbs.hexun.com/e/111219/loading.htm
http://f200-8.bbs.hexun.com/e/111219/loading2.htm
第一个带着小尾巴转动的loading图标画图的思路是，首先画一个圆，然后在圆的边上按顺序画大小逐渐减小的小圆点，在每次刷新画布时改变这一系列的小圆点在大圆边上的位置。
<!doctype html>
<html>
<head>
<meta http-equiv="content-type" content="GBK"/>
<title>loading</title>
<script type="text/javascript">
/*
html5 loading 控件
作者：玉开 博客：http://www.cnblogs.com/yukaizhao/
发布或使用此控件，请保留作者声明
*/
function loading(canvas,options){
this.canvas = canvas;
if(options){
this.radius = options.radius||12;
this.circleLineWidth = options.circleLineWidth||4;
this.circleColor = options.circleColor||'lightgray';
this.dotColor = options.dotColor||'gray';
}else{
this.radius = 12;
this.circelLineWidth = 4;
this.circleColor = 'lightgray';
this.dotColor = 'gray';
}
}
loading.prototype = {
show:function (){
var canvas = this.canvas;
if(!canvas.getContext)return;
if(canvas.__loading)return;
canvas.__loading = this;
var ctx = canvas.getContext('2d');
var radius = this.radius;
var rotators = [{angle:0,radius:1.5},{angle:3/radius,radius:2},{angle:7/radius,radius:2.5},{angle:12/radius,radius:3}];
var me = this;
canvas.loadingInterval = setInterval(function(){
ctx.clearRect(0,0,canvas.width,canvas.height);
var lineWidth = me.circleLineWidth;
var center = {x:canvas.width/2 - radius,y:canvas.height/2-radius};
ctx.beginPath();
ctx.lineWidth = lineWidth;
ctx.strokeStyle = me.circleColor;
ctx.arc(center.x,center.y,radius,0,Math.PI*2);
ctx.closePath();
ctx.stroke();
for(var i=0;i<rotators.length;i++){
var rotatorAngle = rotators[i].currentAngle||rotators[i].angle;
//在圆圈上面画小圆
var rotatorCenter = {x:center.x-(radius)*Math.cos(rotatorAngle) ,y:center.y-(radius)*Math.sin(rotatorAngle)};
var rotatorRadius = rotators[i].radius;
ctx.beginPath();
ctx.fillStyle = me.dotColor;
ctx.arc(rotatorCenter.x,rotatorCenter.y,rotatorRadius,0,Math.PI*2);
ctx.closePath();
ctx.fill();
rotators[i].currentAngle = rotatorAngle+4/radius;
}
},50);
},
hide:function(){
var canvas = this.canvas;
canvas.__loading = false;
if(canvas.loadingInterval){
window.clearInterval(canvas.loadingInterval);
}
var ctx = canvas.getContext('2d');
if(ctx)ctx.clearRect(0,0,canvas.width,canvas.height);
}
};
</script>
</head>
<body>
<canvas id="canvas" width="300" height="100" style="border:1px solid #69c"></canvas>
<p>
<input type="button" onclick="loadingObj.hide()" value="HideLoading"/>
<input type="button" onclick="loadingObj.show()" value="showLoading"/>
</p>
<script>
var loadingObj = new loading(document.getElementById('canvas'),{radius:8,circleLineWidth:3});
loadingObj.show();
</script>
</body>
</html>
第二个较为简单，在一个圆环上有一个相同圆心相同半径的圆弧在不停的转动。画图的步骤是首先画一个圆环，然后画一个不同颜色相同圆心半径的圆弧，在每次刷新画布时改变圆弧的起始角度。
<!doctype html>
<html>
<head>
<meta http-equiv="content-type" content="text/html;charset=gbk"/>
<title>loading</title>
<script>
/*
html5 loading 控件
作者：玉开 博客：http://www.cnblogs.com/yukaizhao/
发布或使用此控件，请保留作者声明
*/
function loading(canvas,options){
this.canvas = canvas;
if(options){
this.radius = options.radius||12;
this.circleLineWidth = options.circleLineWidth||4;
this.circleColor = options.circleColor||'lightgray';
this.moveArcColor = options.moveArcColor||'gray';
}else{
this.radius = 12;
this.circelLineWidth = 4;
this.circleColor = 'lightgray';
this.moveArcColor = 'gray';
}
}
loading.prototype = {
show:function (){
var canvas = this.canvas;
if(!canvas.getContext)return;
if(canvas.__loading)return;
canvas.__loading = this;
var ctx = canvas.getContext('2d');
var radius = this.radius;
var me = this;
var rotatorAngle = Math.PI*1.5;
var step = Math.PI/6;
canvas.loadingInterval = setInterval(function(){
ctx.clearRect(0,0,canvas.width,canvas.height);
var lineWidth = me.circleLineWidth;
var center = {x:canvas.width/2 - radius,y:canvas.height/2-radius};
ctx.beginPath();
ctx.lineWidth = lineWidth;
ctx.strokeStyle = me.circleColor;
ctx.arc(center.x,center.y,radius,0,Math.PI*2);
ctx.closePath();
ctx.stroke();
//在圆圈上面画小圆
ctx.beginPath();
ctx.strokeStyle = me.moveArcColor;
ctx.arc(center.x,center.y,radius,rotatorAngle,rotatorAngle+Math.PI*.45);
ctx.stroke();
rotatorAngle+=step;
},50);
},
hide:function(){
var canvas = this.canvas;
canvas.__loading = false;
if(canvas.loadingInterval){
window.clearInterval(canvas.loadingInterval);
}
var ctx = canvas.getContext('2d');
if(ctx)ctx.clearRect(0,0,canvas.width,canvas.height);
}
};
</script>
</head>
<body>
<canvas id="canvas" width="300" height="100" style="border:1px solid #69c">您的浏览器不支持html5哟</canvas>
<p>
<input type="button" onclick="loadingObj.hide()" value="HideLoading"/>
<input type="button" onclick="loadingObj.show()" value="showLoading"/>
</p>
<script>
var loadingObj = new loading(document.getElementById('canvas'),{radius:8,circleLineWidth:3});
loadingObj.show();
</script>
</body>
</html>
目前从移动设备对Html5的支持来看，html5大有可为。
天下大势，合久必分，分久必和。PC开发时web应用在很大程度上统一了客户端程序；而现在移动开发使用不同的系统不同的语言，将来大多数应用必然会统一到一种语言。这种语言必然是html5+javascript.