本文實例講述了js抽獎轉盤實現方法。分享給大家供大家參考，具體如下：

HTML 這里.left 固定了圓的寬度和高度，還有canvas也設置了固定寬高 繪制圓心的坐標也就出來了 (203,203)

抽獎轉盤是由一個大圓和一個內圓完成 ；大圓負責繪制上獎品 ，內圓負責確定指針的位置，指針直接使用圖片，決定位置確定

<div class='left'><div style='background:#1bacff;border-radius: 50%'><canvas height='406px'></canvas><img src='http://www.b3g6.com/bcjs/sp2/point.png'/></div></div>

外圓留空多少的問題

PS里查看間距是多少，此處圓心(203,203) 大圓的半徑就是203-10 =193

這個數值在下圖里設置

JS

<script type='text/javascript'> var turnplate={ restaraunts:[],//大轉盤獎品名稱 colors:[],//大轉盤獎品區塊對應背景顏色 outsideRadius:193,//大轉盤外圓的半徑 192 textRadius:155,//大轉盤獎品位置距離圓心的距離 insideRadius:68,//大轉盤內圓的半徑 startAngle:0,//開始角度 bRotate:false//false:停止;ture:旋轉 }; $(document).ready(function(){ //動態添加大轉盤的獎品與獎品區域背景顏色 turnplate.restaraunts = ['50元代金券', '升職加薪', '100元代金券', '財源滾滾', '200元代金券', '愛情甜蜜 ', '500元代金券', '變美變帥']; turnplate.colors = ['#1b62ca', '#1bacff', '#1b62ca', '#1bacff','#1b62ca', '#1bacff', '#1b62ca', '#1bacff']; var rotateTimeOut = function (){$(’#wheelcanvas’).rotate({ angle:0, animateTo:2160, duration:8000, callback:function (){ alert(’網絡超時，請檢查您的網絡設置！’); }}); }; //旋轉轉盤 item:獎品位置; txt：提示語; var rotateFn = function (item, txt){var angles = item * (360 / turnplate.restaraunts.length) - (360 / (turnplate.restaraunts.length*2));if(angles<270){ angles = 270 - angles;}else{ angles = 360 - angles + 270;}$(’#wheelcanvas’).stopRotate();$(’#wheelcanvas’).rotate({ angle:0, animateTo:angles+1800, duration:8000, callback:function (){ alert(txt); turnplate.bRotate = !turnplate.bRotate; }}); }; $(’.pointer’).click(function (){if(turnplate.bRotate)return;turnplate.bRotate = !turnplate.bRotate;//獲取隨機數(獎品個數范圍內)var item = rnd(1,turnplate.restaraunts.length);//獎品數量等于10,指針落在對應獎品區域的中心角度[252, 216, 180, 144, 108, 72, 36, 360, 324, 288]rotateFn(item, turnplate.restaraunts[item-1]);/* switch (item) { case 1: rotateFn(252, turnplate.restaraunts[0]); break; case 2: rotateFn(216, turnplate.restaraunts[1]); break; case 3: rotateFn(180, turnplate.restaraunts[2]); break; case 4: rotateFn(144, turnplate.restaraunts[3]); break; case 5: rotateFn(108, turnplate.restaraunts[4]); break; case 6: rotateFn(72, turnplate.restaraunts[5]); break; case 7: rotateFn(36, turnplate.restaraunts[6]); break; case 8: rotateFn(360, turnplate.restaraunts[7]); break; case 9: rotateFn(324, turnplate.restaraunts[8]); break; case 10: rotateFn(288, turnplate.restaraunts[9]); break; } */console.log(item); }); }); function rnd(n, m){ var random = Math.floor(Math.random()*(m-n+1)+n); return random; } //頁面所有元素加載完畢后執行drawRouletteWheel()方法對轉盤進行渲染 window.onload=function(){ drawRouletteWheel(); }; function drawRouletteWheel() { var canvas = document.getElementById('wheelcanvas'); if (canvas.getContext) {//根據獎品個數計算圓周角度var arc = Math.PI / (turnplate.restaraunts.length/2);//圓周率/ 獎品數量除以2var ctx = canvas.getContext('2d');//在給定矩形內清空一個矩形ctx.clearRect(0,0,422,422);//strokeStyle 屬性設置或返回用于筆觸的顏色、漸變或模式ctx.strokeStyle = '#FFBE04';//font 屬性設置或返回畫布上文本內容的當前字體屬性ctx.font = ’16px Microsoft YaHei’;// 繪制圓 （弧形）for(var i = 0; i < turnplate.restaraunts.length; i++) { var angle = turnplate.startAngle + i * arc; ctx.fillStyle = turnplate.colors[i]; ctx.beginPath(); //arc(x,y,r,起始角,結束角,繪制方向) 方法創建弧/曲線（用于創建圓或部分圓） ctx.arc(203, 203, turnplate.outsideRadius, angle, angle + arc, false);//繪制外圓 ctx.arc(203, 203, turnplate.insideRadius, angle + arc, angle, true);//繪制內圓 ctx.stroke(); ctx.fill(); //鎖畫布(為了保存之前的畫布狀態) ctx.save(); //----繪制獎品開始---- ctx.fillStyle = '#FFF';/*獎品文字顏色*/ var text = turnplate.restaraunts[i]; var line_height = 17; //translate方法重新映射畫布上的 (0,0) 位置 ctx.translate(211 + Math.cos(angle + arc / 2) * turnplate.textRadius, 211 + Math.sin(angle + arc / 2) * turnplate.textRadius); //rotate方法旋轉當前的繪圖 ctx.rotate(angle + arc / 2 + Math.PI / 2); /** 下面代碼根據獎品類型、獎品名稱長度渲染不同效果，如字體、顏色、圖片效果。(具體根據實際情況改變) **/ if(text.indexOf('M')>0){//流量包 var texts = text.split('M'); for(var j = 0; j<texts.length; j++){ ctx.font = j == 0?’bold 20px Microsoft YaHei’:’16px Microsoft YaHei’; if(j == 0){ctx.fillText(texts[j]+'M', -ctx.measureText(texts[j]+'M').width / 2, j * line_height); }else{ctx.fillText(texts[j], -ctx.measureText(texts[j]).width / 2, j * line_height); } } }else if(text.indexOf('M') == -1 && text.length>6){//獎品名稱長度超過一定范圍 text = text.substring(0,6)+'||'+text.substring(6); var texts = text.split('||'); for(var j = 0; j<texts.length; j++){ ctx.fillText(texts[j], -ctx.measureText(texts[j]).width / 2, j * line_height); } }else{ //在畫布上繪制填色的文本。文本的默認顏色是黑色 //measureText()方法返回包含一個對象，該對象包含以像素計的指定字體寬度 ctx.fillText(text, -ctx.measureText(text).width / 2, 0); } //添加對應圖標 if(text.indexOf('閃幣')>0){ var img= document.getElementById('shan-img'); img.onload=function(){ ctx.drawImage(img,-15,10); }; ctx.drawImage(img,-15,10); }else if(text.indexOf('謝謝參與')>=0){ var img= document.getElementById('sorry-img'); img.onload=function(){ ctx.drawImage(img,-15,10); }; ctx.drawImage(img,-15,10); } //把當前畫布返回（調整）到上一個save()狀態之前 ctx.restore(); //----繪制獎品結束----} } } </script>

引用jquery

在加載以下JS

/* ????????????? www.datouwang.com */(function($) {var supportedCSS,styles=document.getElementsByTagName('head')[0].style,toCheck='transformProperty WebkitTransform OTransform msTransform MozTransform'.split(' ');for (var a=0;a<toCheck.length;a++) if (styles[toCheck[a]] !== undefined) supportedCSS = toCheck[a];// Bad eval to preven google closure to remove it from code o_O// After compresion replace it back to var IE = ’v’ == ’v’var IE = eval(’'v'=='v'’);jQuery.fn.extend({ rotate:function(parameters) { if (this.length===0||typeof parameters=='undefined') return; if (typeof parameters=='number') parameters={angle:parameters}; var returned=[]; for (var i=0,i0=this.length;i<i0;i++) {var element=this.get(i);if (!element.Wilq32 || !element.Wilq32.PhotoEffect) { var paramClone = $.extend(true, {}, parameters); var newRotObject = new Wilq32.PhotoEffect(element,paramClone)._rootObj; returned.push($(newRotObject));}else { element.Wilq32.PhotoEffect._handleRotation(parameters);} } return returned; }, getRotateAngle: function(){ var ret = []; for (var i=0,i0=this.length;i<i0;i++) {var element=this.get(i);if (element.Wilq32 && element.Wilq32.PhotoEffect) { ret[i] = element.Wilq32.PhotoEffect._angle;} } return ret; }, stopRotate: function(){ for (var i=0,i0=this.length;i<i0;i++) {var element=this.get(i);if (element.Wilq32 && element.Wilq32.PhotoEffect) { clearTimeout(element.Wilq32.PhotoEffect._timer);} } }});// Library agnostic interfaceWilq32=window.Wilq32||{};Wilq32.PhotoEffect=(function(){if (supportedCSS) {return function(img,parameters){img.Wilq32 = {PhotoEffect: this}; this._img = this._rootObj = this._eventObj = img; this._handleRotation(parameters);}} else {return function(img,parameters) {// Make sure that class and id are also copied - just in case you would like to refeer to an newly created object this._img = img;this._rootObj=document.createElement(’span’);this._rootObj.style.display='inline-block';this._rootObj.Wilq32 = {PhotoEffect: this};img.parentNode.insertBefore(this._rootObj,img);if (img.complete) {this._Loader(parameters);} else {var self=this;// TODO: Remove jQuery dependencyjQuery(this._img).bind('load', function(){self._Loader(parameters);});}}}})();Wilq32.PhotoEffect.prototype={ _setupParameters : function (parameters){this._parameters = this._parameters || {}; if (typeof this._angle !== 'number') this._angle = 0 ; if (typeof parameters.angle==='number') this._angle = parameters.angle; this._parameters.animateTo = (typeof parameters.animateTo==='number') ? (parameters.animateTo) : (this._angle); this._parameters.step = parameters.step || this._parameters.step || null;this._parameters.easing = parameters.easing || this._parameters.easing || function (x, t, b, c, d) { return -c * ((t=t/d-1)*t*t*t - 1) + b; }this._parameters.duration = parameters.duration || this._parameters.duration || 1000; this._parameters.callback = parameters.callback || this._parameters.callback || function(){}; if (parameters.bind && parameters.bind != this._parameters.bind) this._BindEvents(parameters.bind); },_handleRotation : function(parameters){ this._setupParameters(parameters); if (this._angle==this._parameters.animateTo) { this._rotate(this._angle); } else {this._animateStart(); }},_BindEvents:function(events){if (events && this._eventObj) { // Unbinding previous Events if (this._parameters.bind){var oldEvents = this._parameters.bind;for (var a in oldEvents) if (oldEvents.hasOwnProperty(a)) // TODO: Remove jQuery dependency jQuery(this._eventObj).unbind(a,oldEvents[a]); } this._parameters.bind = events;for (var a in events) if (events.hasOwnProperty(a)) // TODO: Remove jQuery dependencyjQuery(this._eventObj).bind(a,events[a]);}},_Loader:(function(){if (IE)return function(parameters){var width=this._img.width;var height=this._img.height;this._img.parentNode.removeChild(this._img);this._vimage = this.createVMLNode(’image’);this._vimage.src=this._img.src;this._vimage.style.height=height+'px';this._vimage.style.width=width+'px';this._vimage.style.position='absolute'; // FIXES IE PROBLEM - its only rendered if its on absolute position!this._vimage.style.top = '0px';this._vimage.style.left = '0px';/* Group minifying a small 1px precision problem when rotating object */this._container = this.createVMLNode(’group’);this._container.style.width=width;this._container.style.height=height;this._container.style.position='absolute';this._container.setAttribute(’coordsize’,width-1+’,’+(height-1)); // This -1, -1 trying to fix ugly problem with small displacement on IEthis._container.appendChild(this._vimage);this._rootObj.appendChild(this._container);this._rootObj.style.position='relative'; // FIXES IE PROBLEMthis._rootObj.style.width=width+'px';this._rootObj.style.height=height+'px';this._rootObj.setAttribute(’id’,this._img.getAttribute(’id’));this._rootObj.className=this._img.className; this._eventObj = this._rootObj; this._handleRotation(parameters);}elsereturn function (parameters){this._rootObj.setAttribute(’id’,this._img.getAttribute(’id’));this._rootObj.className=this._img.className;this._width=this._img.width;this._height=this._img.height;this._widthHalf=this._width/2; // used for optimisationthis._heightHalf=this._height/2;// used for optimisationvar _widthMax=Math.sqrt((this._height)*(this._height) + (this._width) * (this._width));this._widthAdd = _widthMax - this._width;this._heightAdd = _widthMax - this._height;// widthMax because maxWidth=maxHeightthis._widthAddHalf=this._widthAdd/2; // used for optimisationthis._heightAddHalf=this._heightAdd/2;// used for optimisationthis._img.parentNode.removeChild(this._img);this._aspectW = ((parseInt(this._img.style.width,10)) || this._width)/this._img.width;this._aspectH = ((parseInt(this._img.style.height,10)) || this._height)/this._img.height;this._canvas=document.createElement(’canvas’);this._canvas.setAttribute(’width’,this._width);this._canvas.style.position='relative';this._canvas.style.left = -this._widthAddHalf + 'px';this._canvas.style.top = -this._heightAddHalf + 'px';this._canvas.Wilq32 = this._rootObj.Wilq32;this._rootObj.appendChild(this._canvas);this._rootObj.style.width=this._width+'px';this._rootObj.style.height=this._height+'px'; this._eventObj = this._canvas;this._cnv=this._canvas.getContext(’2d’); this._handleRotation(parameters);}})(),_animateStart:function(){if (this._timer) {clearTimeout(this._timer);}this._animateStartTime = +new Date;this._animateStartAngle = this._angle;this._animate();}, _animate:function() { var actualTime = +new Date; var checkEnd = actualTime - this._animateStartTime > this._parameters.duration; // TODO: Bug for animatedGif for static rotation ? (to test) if (checkEnd && !this._parameters.animatedGif) { clearTimeout(this._timer); } else { if (this._canvas||this._vimage||this._img) { var angle = this._parameters.easing(0, actualTime - this._animateStartTime, this._animateStartAngle, this._parameters.animateTo - this._animateStartAngle, this._parameters.duration); this._rotate((~~(angle*10))/10); } if (this._parameters.step) {this._parameters.step(this._angle); } var self = this; this._timer = setTimeout(function() { self._animate.call(self); }, 10); } // To fix Bug that prevents using recursive function in callback I moved this function to back if (this._parameters.callback && checkEnd){ this._angle = this._parameters.animateTo; this._rotate(this._angle); this._parameters.callback.call(this._rootObj); } },_rotate : (function(){var rad = Math.PI/180;if (IE)return function(angle){ this._angle = angle;this._container.style.rotation=(angle%360)+'deg';}else if (supportedCSS)return function(angle){ this._angle = angle;this._img.style[supportedCSS]='rotate('+(angle%360)+'deg)';}else return function(angle){ this._angle = angle;angle=(angle%360)* rad;// clear canvasthis._canvas.width = this._width+this._widthAdd;this._canvas.height = this._height+this._heightAdd;// REMEMBER: all drawings are read from backwards.. so first function is translate, then rotate, then translate, translate..this._cnv.translate(this._widthAddHalf,this._heightAddHalf);// at least center image on screenthis._cnv.translate(this._widthHalf,this._heightHalf);// we move image back to its orginal this._cnv.rotate(angle);// rotate imagethis._cnv.translate(-this._widthHalf,-this._heightHalf);// move image to its center, so we can rotate around its centerthis._cnv.scale(this._aspectW,this._aspectH); // SCALE - if needed ;)this._cnv.drawImage(this._img, 0, 0);// First - we draw image}})()}if (IE){Wilq32.PhotoEffect.prototype.createVMLNode=(function(){document.createStyleSheet().addRule('.rvml', 'behavior:url(#default#VML)');try {!document.namespaces.rvml && document.namespaces.add('rvml', 'urn:schemas-microsoft-com:vml');return function (tagName) {return document.createElement(’<rvml:’ + tagName + ’ class='rvml'>’);};} catch (e) {return function (tagName) {return document.createElement(’<’ + tagName + ’ xmlns='urn:schemas-microsoft.com:vml' class='rvml'>’);};}})();}})(jQuery);

感興趣的朋友可以使用在線HTML/CSS/JavaScript代碼運行工具：http://tools.jb51.net/code/HtmlJsRun 測試上述代碼運行效果。

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希望本文所述對大家JavaScript程序設計有所幫助。