提到在线绘图，目前最流行的技术应该属Flex了（可参见另一篇文章：15个强大的在线图片编辑器 ），另外Silverlight在此方面也很有潜力。相比之下，诸多轻量级的客户端矢量图形绘制技术却显得有点鲜为人知。谨以此文总结我一年以来收集的此方面的相关资料与心得，与大家分享！
在一些web客户端客户端开发中，轻量级客户端矢量图形绘制技术还能够起到重要的作用。
1. VML 矢量标记语言
维基百科对VML的解释如下：
VML(Vector Markup Language) is an application of Extensible Markup Language (XML) 1.0 which defines a format for the encoding of vector information together with additional markup to describe how that information may be displayed and edited.
例子：使用VML与鼠标绘图：
online drawing
<SCRIPT LANGUAGE="JavaScript">
var x,y,a,b;
function drawline(fromX,fromY,toX,toY){
var strElement= "<v:Line id='line_"+fromX+"_"+fromY+"_"+toX+"_"+toY+"' from='" + fromX + "," + fromY + "' to='" + toX + "," + toY + "' strokecolor='red'></v:Line>";
var newPoint = document.createElement(strElement);
document.getElementById("map").appendChild(newPoint);
}
function draw(){
if(x==undefined&&b==undefined){x=window.event.x;y=window.event.y;return false;}
a=window.event.x;b=window.event.y;
drawline(x,y,a,b)
x=a;y=b;
}
function draws(){
if(x==undefined&&b==undefined){return false;}
if(x==window.event.x&&b==window.event.y){return false;}
if(document.getElementById("TempLine")){document.getElementById("TempLine").outerHTML=""}
var strElement= "<v:Line id='TempLine' from='" + x + "," + y + "' to='" + window.event.x + "," + window.event.y + "' strokecolor='red'></v:Line>";
var newPoint = document.createElement(strElement);
document.getElementById("map").appendChild(newPoint);
}
</SCRIPT>
<html xmlns:v="urn:schemas-microsoft-com:vml">
<HEAD>
<META http-equiv="Content-Type" content="text/html;Charset=gb2312">
<title>vml example</title>
<STYLE>
v\:*{behavior:url(#default#VML);}/*define V as VML variable*/
</STYLE>
</HEAD>
<BODY>
<table border="1" align="center">
<tr>
<td><div id="map" style="width:600px;height:500px;background-color:#cccccc;position:relative;" onmousedown="draw();" onmousemove="draws()"></div></td>
</tr>
</table>
</body>
</html>
VML作为一种XML的扩展，还在数据处理上很有用途，这里还有个例子：
例子：VML+XML绘制树型图表(Create a Tree Graph by VML+XML)
code is pick from internet, connect me if you are the author, Thanks.
data.xml
<?xml version="1.0" encoding="utf-8"?>
<Company>
<Manager>
<DepartMentA>
<StafferA1 />
<StafferA2 />
<StafferA3 />
</DepartMentA>
<DepartMentB>
<StafferB1 />
<StafferB2 />
<StafferB3 />
</DepartMentB>
<DepartMentC>
<StafferC1 />
<StafferC2 />
<StafferC3 />
</DepartMentC>
</Manager>
</Company>
vml.htm
<html xmlns:v="urn:schemas-microsoft-com:vml">
<head>
<META HTTP-EQUIV="MSThemeCompatible" CONTENT="Yes">
<style type="text/css">
v\:*{
behavior:url(#default#VML);
}
v\:RoundRect{
text-align:center;
position:relative;
}
v\:TextBox{
vertical-align:middle;
font-size:13px;
}
</style>
<script type="text/javascript">
function $(id){
return document.getElementById(id);
}
function Point2D(x,y){
this.x = x;
this.y = y;
}
function Xml2Vml(xmlFile){
this.XML = new ActiveXObject("MSXML2.DOMDocument.5.0");
this.XML.async=false;
this.XML.load(xmlFile);
this.SpanX = 10;
this.SpanY = 25;
this.ItemWidth = 100;
this.ItemHeight = 25;
this.VmlRoot = document.createElement('<v:group coordsize="1000,1000" id="vml" style="width:1000px;height:1000px;">');
}
Xml2Vml.prototype.RecursiveParse = function(rootNode,offset){
var allChild = rootNode.childNodes;
var xOffset = offset.x;
var yOffset = offset.y;
if(allChild.length==0){
rootNode.setAttribute("LeftX",xOffset);
rootNode.setAttribute("RightX",xOffset+this.ItemWidth);
xOffset += this.SpanX + this.ItemWidth;
}else{
for(var i=0;i<allChild.length;i++){
var w = this.RecursiveParse(allChild[i],new Point2D(xOffset,yOffset+2*this.SpanY+this.ItemHeight));
xOffset += this.SpanX + w;
}
rootNode.setAttribute("LeftX",(parseInt(allChild[0].getAttribute("LeftX")) + parseInt(allChild[0].getAttribute("RightX")))/2);
rootNode.setAttribute("RightX",(parseInt(allChild[allChild.length-1].getAttribute("LeftX")) + parseInt(allChild[allChild.length-1].getAttribute("RightX")))/2);
}
rootNode.setAttribute("PosY",yOffset);
return xOffset-offset.x-this.SpanX;
}
Xml2Vml.prototype.ParseXml = function(){
this.RecursiveParse(this.XML.documentElement,new Point2D(0,0));
}
Xml2Vml.prototype.RecursiveRender = function(xmlNode){
var allChild = xmlNode.childNodes;
var xl = xmlNode.getAttribute("LeftX");
var xr = xmlNode.getAttribute("RightX");
var x = (parseInt(xl)+parseInt(xr))/2;
var y = xmlNode.getAttribute("PosY");
var str = xmlNode.tagName;
if(xmlNode!=this.XML.documentElement) this.VmlRoot.appendChild(document.createElement('<v:line from="'+x+','+y+'" to="'+x+','+(parseInt(y)+this.SpanY)+'" />'));
y=parseInt(y)+this.SpanY;
var RoundRect = document.createElement('<v:RoundRect style="width:'+this.ItemWidth+'px;height:'+this.ItemHeight+'px;left:'+(x-this.ItemWidth/2)+'px;top:'+y+'px" align="center">')
RoundRect.appendChild(document.createElement('<v:shadow on="True" type="single" color="#b3b3b3" offset="5px,5px"/>'));
var TextBox = document.createElement('<v:TextBox />');
TextBox.innerHTML = str;
RoundRect.appendChild(TextBox);
this.VmlRoot.appendChild(RoundRect);
if(allChild.length>0){
y += this.ItemHeight+this.SpanY;
this.VmlRoot.appendChild(document.createElement('<v:line from="'+x+','+(y-this.SpanY)+'" to="'+x+','+y+'" />'));
xl = (parseInt(allChild[0].getAttribute("LeftX")) + parseInt(allChild[0].getAttribute("RightX")))/2;
xr = (parseInt(allChild[allChild.length-1].getAttribute("LeftX")) + parseInt(allChild[allChild.length-1].getAttribute("RightX")))/2;
this.VmlRoot.appendChild(document.createElement('<v:line from="'+xl+','+y+'" to="'+xr+','+y+'" />'));
for(var i=0;i<allChild.length;i++) this.RecursiveRender(allChild[i]);
}
}
Xml2Vml.prototype.RenderVml = function(){
this.RecursiveRender(this.XML.documentElement);
}
</script>
</head>
<body>
<center>
<div id="div" style="WIDTH: 1000px; HEIGHT: 1000px"></div>
</center>
<script type="text/javascript">
var Ins = new Xml2Vml("data.xml");
Ins.ParseXml();
Ins.RenderVml();
$("div").appendChild(Ins.VmlRoot);
</script>
</body>
</html>
VML的相关资料：
http://www.w3.org/TR/NOTE-VML
http://en.wikipedia.org/wiki/Vector_Markup_Language
http://www.vml.org/Wnew.html
VML的在线案例：
http://www.tool.la/VMLPalette/
注：VML只支持IE5 以上的IE浏览器，请参见：
http://www.causeway.co.uk/demos/vml/index.htm
To view these charts you will need a VML enabled browser; this means IE5 or above with the VML component installed. Please don't be too annoyed if this page looks a complete mess in Firefox or Opera - VML is a Microsoft-specific format and will never be supported by standards-aware browsers.
2. SVG可扩展矢量图形
W3C网站对SVG的介绍：
SVG(Scalable Vector Graphics ) is a language for describing two-dimensional graphics and graphical applications in XML. SVG 1.1 is a W3C Recommendation and forms the core of the current SVG developments. SVG Tiny 1.2 is the specification currently being developed as the core of the SVG 1.2 language (comments welcome). The SVG Mobile Profiles: SVG Basic and SVG Tiny are targeted to resource-limited devices and are part of the 3GPP platform for third generation mobile phones. SVG Print is a set of guidelines to produce final-form documents in XML suitable for archiving and printing. Read more about SVG.
严格的来说，SVG并不是一种轻量级的绘图方案，因为它需要安装Adobe的SVG Viewer插件（2.78M），但SVG同样也是基于XML的，其强大的功能可以轻松的制作出各种动态和静态图型：
大量SVG例子：
下转自中国w3c联盟
动态
普通效果
http://www.adobe.com/svg/dynamic/transformations2.html
无JS干预效果
http://www.adobe.com/svg/dynamic/declarative.html
JS干预效果
http://www.adobe.com/svg/dynamic/javascript.html
鼠标事件效果，注意可以在HTML元素中干预效果，甚至可以在各个不同的SVG间互相干预
http://www.adobe.com/svg/dynamic/mouseevents.html
键盘事件效果，鼠标点击SVG后敲击键盘，如果字体完全消失，需要再点击
http://www.adobe.com/svg/dynamic/keyboardevents.html
动态插入对象
http://www.adobe.com/svg/dynamic/insertion.html
语言支持演示，支持国际任何语言(拿了日本的语言，中国啊，自强！)
http://www.adobe.com/svg/dynamic/insertion.html
SVG优秀的压缩算法及与JPG、GIF的质量比较
http://www.adobe.com/svg/workflow/optimizing.html
浏览插件的自动安装
http://www.adobe.com/svg/workflow/autoinstall.html
SVG在GoLive、Office、FramwMaker中的使用
http://www.adobe.com/svg/workflow/workflow.html
--------------
静态
点击以显示不同区域
http://www.adobe.com/svg/basics/boundbox.html
动态改变SVG字体及文字内容(无中文字体)
http://www.adobe.com/svg/basics/text.html
动态改变CSS
http://www.adobe.com/svg/basics/css.html
填充
http://www.adobe.com/svg/basics/fills.html
加边
http://www.adobe.com/svg/basics/strokes.html
渐变
http://www.adobe.com/svg/basics/grads.html
滤镜特效1、2
http://www.adobe.com/svg/basics/filtereffects.html
http://www.adobe.com/svg/basics/filtereffects2.html
与传统位图(Jpeg、Gif、Png)的结合
http://www.adobe.com/svg/basics/jpgs.html
ICC标准的色彩支持
http://www.adobe.com/svg/basics/icc.html
选择可见元素的设置
http://www.adobe.com/svg/basics/printing.html
SVG参考资料：
http://www.w3.org/Graphics/SVG/
3. Canvans
Firefox官方网站对Canvans的介绍：
<canvas>是一个新的HTML元素，这个元素可以被Script语言(通常是JavaScript)用来绘制图形。例如可以用它来画图、合成图象、或做简单的(和不那么简单的)动画。右面的图象展示了一些<canvas>的应用示例，我们将会在此教程中看到他们的实现。
注意：Canvans是HTML5标准中的新技术，这意味着所有不支持HTML5的浏览器都不能支持Canvans，包括IE
并不是所有现代浏览器都支持<canvas>元素，所以你需要 Firefox 1.5或更新版本、或者其他基于Gecko的浏览器例如Opera 9、或者最近版本的Safari才能看到所有示例的动作。
例子：简单Canvans例子，来自FF社区
请使用FF或Safari观看
<html>
<head>
<title>A canvas fillRect, strokeRect and clearRect example</title>
<meta name="DC.creator" content="Kamiel Martinet, http://www.martinet.nl/">
<meta name="DC.publisher" content="Mozilla Developer Center, http://developer.mozilla.org">
<script type="text/javascript">
function drawShape(){
// get the canvas element using the DOM
var canvas = document.getElementById('tutorial');
// Make sure we don't execute when canvas isn't supported
if (canvas.getContext){
// use getContext to use the canvas for drawing
var ctx = canvas.getContext('2d');
// Draw shapes
ctx.fillRect(25,25,100,100);
ctx.clearRect(45,45,60,60);
ctx.strokeRect(50,50,50,50);
} else {
alert('You need Safari or Firefox 1.5+ to see this demo.');
}
}
</script>
<style type="text/css">
body { margin: 20px; font-family: arial,verdana,helvetica; background: #fff;}
h1 { font-size: 140%; font-weight:normal; color: #036; border-bottom: 1px solid #ccc; }
canvas { border: 2px solid #000; float: left; margin-right: 20px; margin-bottom: 20px; }
pre { float:left; display:block; background: rgb(238,238,238); border: 1px dashed #666; padding: 15px 20px; margin: 0 0 10px 0; }
</style>
</head>
<body onload="drawShape();">
<h1>An example of fillRect, clearRect and strokeRect</h1>
<div>
<canvas id="tutorial" width="150" height="150"></canvas>
<pre>
function drawShape(){
// get the canvas element using the DOM
var canvas = document.getElementById('tutorial');
// Make sure we don't execute when canvas isn't supported
if (canvas.getContext){
// use getContext to use the canvas for drawing
var ctx = canvas.getContext('2d');
// Draw shapes
ctx.fillRect(25,25,100,100);
ctx.clearRect(45,45,60,60);
ctx.strokeRect(50,50,50,50);
}
}
</pre>
</div>
</body>
</html>
Canvans不仅能够绘制2D、3D的矢量图形，还可以与JS交互来实现一些复杂的动画：
Canvans教程：
https://developer.mozilla.org/cn/Canvas_tutorial
Canvas示例集
Canvas articles and other resources
4. 推荐的第三方开源框架：
除了上述三种技术之外，一些开源的WEB绘图框架也做的很好，尤其是在浏览器兼容方面，在此向大家推荐下列两个：
http://www.c-point.com/javascript_vector_draw.htm
http://www.walterzorn.com/jsgraphics/jsgraphics_e.htm
文章写的仓促，其实这方面技术有很深，不足之处请多多补充
Thanks.
