我们经常参加各种电商优惠活动，比如购买达到一定数额进行抽奖活动，在比如微信抽奖，淘宝抽奖，迅雷赚钱宝圆盘抽奖活动等。这些抽奖活动部分就是由HTML5的Canvas来制作的，今天就为大家分享一下如何使用HTML5的Canvas来制作圆盘抽奖功能。老规矩，先看下效果图吧：
再来看看Canvas的几个主要api：
全部源代码如下：
<!DOCTYPE html><html lang="zh-cn"><head><meta charset="UTF-8"><title>HTML5 Canvas圆盘抽奖应用DEMO演示</title><meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no"><style>*{padding: 0px;margin: 0px;font-size: 16px;font-family: "Microsoft YaHei";}.xttblog_box{width: 300px;height: 300px;margin: 100px auto;position: relative; }.xttblog_box canvas{position: absolute;}#xttblog{background-color: white;border-radius: 100%;}#xttblog01,#xttblog03{left: 50px;top: 50px;z-index: 30;}#xttblog02{left: 75px;top: 75px;z-index: 20;}#xttblog{-o-transform: transform 6s;-ms-transform: transform 6s;-moz-transform: transform 6s; -webkit-transform: transform 6s;transition: transform 6s;-o-transform-origin: 50% 50%;-ms-transform-origin: 50% 50%;-moz-transform-origin: 50% 50%;-webkit-transform-origin: 50% 50%;transform-origin: 50% 50%;}.taoge_btn{width: 60px;height: 60px;left: 120px;top: 120px;border-radius: 100%;position: absolute;cursor: pointer;border: none;background: transparent;outline: none;z-index: 40;}</style><script type="text/javascript" src="http://cdn.bootcss.com/jquery/1.11.3/jquery.min.js"></script><script>$(document).ready(function(){ //旋转角度 var angles; //可抽奖次数 var clickNum = 5; //旋转次数 var rotNum = 0; //中奖公告 var notice = null; //转盘初始化 var color = ["#626262","#787878","rgba(0,0,0,0.5)","#DCC722","white","#FF4350"]; var info = ["谢谢参与"," 1000"," 10"," 500"," 100"," 4999"," 1"," 20"]; var info1 = ['再接再厉',' 元',' 元',' 淘金币',' 元',' 淘金币',' 元',' 淘金币'] canvasRun(); $('#tupBtn').bind('click',function(){ if (clickNum >= 1) { //可抽奖次数减一 clickNum = clickNum-1; //转盘旋转 runCup(); //转盘旋转过程“开始抽奖”按钮无法点击 $('#tupBtn').attr("disabled", true); //旋转次数加一 rotNum = rotNum + 1; //“开始抽奖”按钮无法点击恢复点击 setTimeout(function(){ alert(notice); $('#tupBtn').removeAttr("disabled", true); },6000); } else{ alert("亲，抽奖次数已用光！"); } }); //转盘旋转 function runCup(){ probability(); var degValue = 'rotate('+angles+'deg'+')'; $('#xttblog').css('-o-transform',degValue); //Opera $('#xttblog').css('-ms-transform',degValue); //IE浏览器 $('#xttblog').css('-moz-transform',degValue); //Firefox $('#xttblog').css('-webkit-transform',degValue); //Chrome和Safari $('#xttblog').css('transform',degValue); } //各奖项对应的旋转角度及中奖公告内容 function probability(){ //获取随机数 var num = parseInt(Math.random()*(7 - 0 + 0) + 0); //概率 if ( num == 0 ) { angles = 2160 * rotNum + 1800; notice = info[0] + info1[0]; } //概率 else if ( num == 1 ) { angles = 2160 * rotNum + 1845; notice = info[7] + info1[7]; } //概率 else if ( num == 2 ) { angles = 2160 * rotNum + 1890; notice = info[6] + info1[6]; } //概率 else if ( num == 3 ) { angles = 2160 * rotNum + 1935; notice = info[5] + info1[5]; } //概率 else if ( num == 4 ) { angles = 2160 * rotNum + 1980; notice = info[4] + info1[4]; } //概率 else if ( num == 5 ) { angles = 2160 * rotNum + 2025; notice = info[3] + info1[3]; } //概率 else if ( num == 6 ) { angles = 2160 * rotNum + 2070; notice = info[2] + info1[2]; } //概率 else if ( num == 7 ) { angles = 2160 * rotNum + 2115; notice = info[1] + info1[1]; } } //绘制转盘 function canvasRun(){ var canvas=document.getElementById('xttblog'); var canvas01=document.getElementById('xttblog01'); var canvas03=document.getElementById('xttblog03'); var canvas02=document.getElementById('xttblog02'); var ctx=canvas.getContext('2d'); var ctx1=canvas01.getContext('2d'); var ctx3=canvas03.getContext('2d'); var ctx2=canvas02.getContext('2d'); createCircle(); createCirText(); initPoint(); //外圆 function createCircle(){ var startAngle = 0;//扇形的开始弧度 var endAngle = 0;//扇形的终止弧度 //画一个8等份扇形组成的圆形 for (var i = 0; i< 8; i++){ startAngle = Math.PI*(i/4-1/8); endAngle = startAngle+Math.PI*(1/4); ctx.save(); ctx.beginPath(); ctx.arc(150,150,100, startAngle, endAngle, false); ctx.lineWidth = 120; if (i%2 == 0) { ctx.strokeStyle = color[0]; }else{ ctx.strokeStyle = color[1]; } ctx.stroke(); ctx.restore(); } } //各奖项 function createCirText(){ ctx.textAlign='start'; ctx.textBaseline='middle'; ctx.fillStyle = color[3]; var step = 2*Math.PI/8; for ( var i = 0; i < 8; i++) { ctx.save(); ctx.beginPath(); ctx.translate(150,150); ctx.rotate(i*step); ctx.font = " 20px Microsoft YaHei"; ctx.fillStyle = color[3]; ctx.fillText(info[i],-30,-115,60); ctx.font = " 14px Microsoft YaHei"; ctx.fillText(info1[i],-30,-95,60); ctx.closePath(); ctx.restore(); } } function initPoint(){ //箭头指针 ctx1.beginPath(); ctx1.moveTo(100,24); ctx1.lineTo(90,62); ctx1.lineTo(110,62); ctx1.lineTo(100,24); ctx1.fillStyle = color[5]; ctx1.fill(); ctx1.closePath(); //中间小圆 ctx3.beginPath(); ctx3.arc(100,100,40,0,Math.PI*2,false); ctx3.fillStyle = color[5]; ctx3.fill(); ctx3.closePath(); //小圆文字 ctx3.font = "Bold 20px Microsoft YaHei"; ctx3.textAlign='start'; ctx3.textBaseline='middle'; ctx3.fillStyle = color[4]; ctx3.beginPath(); ctx3.fillText('开始',80,90,40); ctx3.fillText('抽奖',80,110,40); ctx3.fill(); ctx3.closePath(); //中间圆圈 ctx2.beginPath(); ctx2.arc(75,75,75,0,Math.PI*2,false); ctx2.fillStyle = color[2]; ctx2.fill(); ctx2.closePath(); } }});</script></head><body><div> <canvas id="xttblog">抱歉！浏览器不支持。</canvas> <canvas id="xttblog01">抱歉！浏览器不支持。</canvas> <canvas id="xttblog03">抱歉！浏览器不支持。</canvas> <canvas id="xttblog02">抱歉！浏览器不支持。</canvas> <button id="tupBtn"></button></div><!-- 更改系统默认弹窗 --><script type="text/javascript">window.alert = function(str){ var shield = document.createElement("DIV"); shield.id = "shield"; shield.style.position = "absolute"; shield.style.left = "50%"; shield.style.top = "50%"; shield.style.width = "280px"; shield.style.height = "150px"; shield.style.marginLeft = "-140px"; shield.style.marginTop = "-110px"; shield.style.zIndex = "25"; var alertFram = document.createElement("DIV"); alertFram.id="alertFram"; alertFram.style.position = "absolute"; alertFram.style.width = "280px"; alertFram.style.height = "150px"; alertFram.style.left = "50%"; alertFram.style.top = "50%"; alertFram.style.marginLeft = "-140px"; alertFram.style.marginTop = "-110px"; alertFram.style.textAlign = "center"; alertFram.style.lineHeight = "150px"; alertFram.style.zIndex = "300"; strHtml = "<ul style=/"list-style:none;margin:0px;padding:0px;width:100%/">/n"; strHtml += " <li style=/"background:#626262;text-align:left;padding-left:20px;font-size:14px;font-weight:bold;height:25px;line-height:25px;border:1px solid #F9CADE;color:white/">[中奖提醒]</li>/n"; strHtml += " <li style=/"background:#787878;text-align:center;font-size:12px;height:95px;line-height:95px;border-left:1px solid #F9CADE;border-right:1px solid #F9CADE;color:#DCC722/">"+str+"</li>/n"; strHtml += " <li style=/"background:#626262;text-align:center;font-weight:bold;height:30px;line-height:25px; border:1px solid #F9CADE;/"><input type=/"button/" value=/"确 定/" onclick=/"doOk()/" style=/"width:80px;height:20px;background:#626262;color:white;border:1px solid white;font-size:14px;line-height:20px;outline:none;margin-top: 4px/"/></li>/n"; strHtml += "</ul>/n"; alertFram.innerHTML = strHtml; document.body.appendChild(alertFram); document.body.appendChild(shield); this.doOk = function(){ alertFram.style.display = "none"; shield.style.display = "none"; } alertFram.focus(); document.body.onselectstart = function(){return false;};}</script></body></html>以上就是本文的全部内容，希望对大家的学习有所帮助。
原文地址：http://www.xttblog.com/?p=399