javascript基于HTML5 canvas制作画箭头组件

样例：

废话少说，直接上代码：

arrow.js

/**
 * 实现两点间画箭头的功能
 * @author mapleque@163.com
 * @version 1.0
 * @date 2013.05.23
 */
;(function(window,document){
 if (window.mapleque==undefined)
 window.mapleque={};
 if (window.mapleque.arrow!=undefined)
 return;
 
 /**
 * 组件对外接口
 */
 var proc={
 /**
 * 接收canvas对象，并在此上画箭头（箭头起止点已经设置）
 * @param context
 */
 paint:function(context){paint(this,context);},
 /**
 * 设置箭头起止点
 * @param sp起点
 * @param ep终点
 * @param st强度
 */
 set:function(sp,ep,st){init(this,sp,ep,st);},
 /**
 * 设置箭头外观
 * @param args
 */
 setPara:function(args){
  this.size=args.arrow_size;//箭头大小
  this.sharp=args.arrow_sharp;//箭头锐钝
 }
 };
 
 var init=function(a,sp,ep,st){
 a.sp=sp;//起点
 a.ep=ep;//终点
 a.st=st;//强度
 };
 var paint=function(a,context){
 var sp=a.sp;
 var ep=a.ep;
 if (context==undefined)
  return;
 //画箭头主线
 context.beginPath();
 context.moveTo(sp.x,sp.y);
 context.lineTo(ep.x,ep.y);
 //画箭头头部
 var h=_calcH(a,sp,ep,context);
 context.moveTo(ep.x,ep.y);
 context.lineTo(h.h1.x,h.h1.y);
 context.moveTo(ep.x,ep.y);
 context.lineTo(h.h2.x,h.h2.y);
 context.stroke();
 };
 //计算头部坐标
 var _calcH=function(a,sp,ep,context){
 var theta=Math.atan((ep.x-sp.x)/(ep.y-sp.y));
 var cep=_scrollXOY(ep,-theta);
 var csp=_scrollXOY(sp,-theta);
 var ch1={x:0,y:0};
 var ch2={x:0,y:0};
 var l=cep.y-csp.y;
 ch1.x=cep.x+l*(a.sharp||0.025);
 ch1.y=cep.y-l*(a.size||0.05);
 ch2.x=cep.x-l*(a.sharp||0.025);
 ch2.y=cep.y-l*(a.size||0.05);
 var h1=_scrollXOY(ch1,theta);
 var h2=_scrollXOY(ch2,theta);
 return {
  h1:h1,
  h2:h2
  };
 };
 //旋转坐标
 var _scrollXOY=function(p,theta){
 return {
  x:p.x*Math.cos(theta)+p.y*Math.sin(theta),
  y:p.y*Math.cos(theta)-p.x*Math.sin(theta)
 };
 };
 
 var arrow=new Function();
 arrow.prototype=proc;
 window.mapleque.arrow=arrow;
})(window,document);

arrow.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>sample of the arrow</title>
<script type="text/javascript" src="./arrow.js"></script>
</head>
<body>
<canvas width=800 height=600 id="arrowLine">请使用支持HTML5的浏览器</canvas>
<script type="text/javascript">
var cont=document.getElementById("arrowLine").getContext('2d');
var a1=new window.mapleque.arrow();
a1.set({x:350,y:300},{x:200,y:200});
a1.paint(cont);
var a2=new window.mapleque.arrow();
a2.set({x:100,y:100},{x:200,y:250});
a2.paint(cont);
var a3=new window.mapleque.arrow();
a3.set({x:100,y:300},{x:150,y:150});
a3.paint(cont);
var a4=new window.mapleque.arrow();
a4.set({x:350,y:150},{x:150,y:250});
a4.setPara({
 arrow_size:0.5,
 arrow_sharp:0.5
})
a4.paint(cont);
</script>
</body>
</html>