樣例：
廢話少說，直接上代碼：
arrow.js
/** * 實現兩點間畫箭頭的功能 * @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; /** * 組件對外接口 */ var proc={ /** * 接收canvas對象，并在此上畫箭頭（箭頭起止點已經設置） * @param context */ paint:function(context){paint(this,context);}, /** * 設置箭頭起止點 * @param sp起點 * @param ep終點 * @param st強度 */ set:function(sp,ep,st){init(this,sp,ep,st);}, /** * 設置箭頭外觀 * @param args */ setPara:function(args){ this.size=args.arrow_size;//箭頭大小 this.sharp=args.arrow_sharp;//箭頭銳鈍 } }; var init=function(a,sp,ep,st){ a.sp=sp;//起點 a.ep=ep;//終點 a.st=st;//強度 }; var paint=function(a,context){ var sp=a.sp; var ep=a.ep; if (context==undefined) return; //畫箭頭主線 context.beginPath(); context.moveTo(sp.x,sp.y); context.lineTo(ep.x,ep.y); //畫箭頭頭部 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(); }; //計算頭部坐標 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 }; }; //旋轉坐標 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">請使用支持HTML5的瀏覽器</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>新聞熱點
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