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本文实例讲述了js抽奖转盘实现方法。分享给大家供大家参考，具体如下：
HTML 这里.left 固定了圆的宽度和高度，还有canvas也设置了固定宽高 绘制圆心的坐标也就出来了 (203,203)
抽奖转盘是由一个大圆和一个内圆完成 ；大圆负责绘制上奖品 ，内圆负责确定指针的位置，指针直接使用图片，决定位置确定
<div class="left"> <div class="turnplate" style="background:#1bacff;border-radius: 50%"> <canvas class="item" id="wheelcanvas" width="406px" height="406px"></canvas> <img class="pointer" src="/UploadFiles/2021-04-02/point.png">
外圆留空多少的问题
PS里查看间距是多少，此处圆心(203,203) 大圆的半径就是203-10 =193
这个数值在下图里设置
JS
<script type="text/javascript"> var turnplate={ restaraunts:[], //大转盘奖品名称 colors:[], //大转盘奖品区块对应背景颜色 outsideRadius:193, //大转盘外圆的半径 192 textRadius:155, //大转盘奖品位置距离圆心的距离 insideRadius:68, //大转盘内圆的半径 startAngle:0, //开始角度 bRotate:false //false:停止;ture:旋转 }; $(document).ready(function(){ //动态添加大转盘的奖品与奖品区域背景颜色 turnplate.restaraunts = ["50元代金券", "升职加薪", "100元代金券", "财源滚滚", "200元代金券", "爱情甜蜜 ", "500元代金券", "变美变帅"]; turnplate.colors = ["#1b62ca", "#1bacff", "#1b62ca", "#1bacff","#1b62ca", "#1bacff", "#1b62ca", "#1bacff"]; var rotateTimeOut = function (){ $('#wheelcanvas').rotate({ angle:0, animateTo:2160, duration:8000, callback:function (){ alert('网络超时，请检查您的网络设置！'); } }); }; //旋转转盘 item:奖品位置; txt：提示语; 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; //获取随机数(奖品个数范围内) var item = rnd(1,turnplate.restaraunts.length); //奖品数量等于10,指针落在对应奖品区域的中心角度[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; } //页面所有元素加载完毕后执行drawRouletteWheel()方法对转盘进行渲染 window.onload=function(){ drawRouletteWheel(); }; function drawRouletteWheel() { var canvas = document.getElementById("wheelcanvas"); if (canvas.getContext) { //根据奖品个数计算圆周角度 var arc = Math.PI / (turnplate.restaraunts.length/2);//圆周率/ 奖品数量除以2 var ctx = canvas.getContext("2d"); //在给定矩形内清空一个矩形 ctx.clearRect(0,0,422,422); //strokeStyle 属性设置或返回用于笔触的颜色、渐变或模式 ctx.strokeStyle = "#FFBE04"; //font 属性设置或返回画布上文本内容的当前字体属性 ctx.font = '16px Microsoft YaHei'; // 绘制圆 （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,结束角,绘制方向) 方法创建弧/曲线（用于创建圆或部分圆） ctx.arc(203, 203, turnplate.outsideRadius, angle, angle + arc, false);//绘制外圆 ctx.arc(203, 203, turnplate.insideRadius, angle + arc, angle, true);//绘制内圆 ctx.stroke(); ctx.fill(); //锁画布(为了保存之前的画布状态) ctx.save(); //----绘制奖品开始---- ctx.fillStyle = "#FFF";/*奖品文字颜色*/ var text = turnplate.restaraunts[i]; var line_height = 17; //translate方法重新映射画布上的 (0,0) 位置 ctx.translate(211 + Math.cos(angle + arc / 2) * turnplate.textRadius, 211 + Math.sin(angle + arc / 2) * turnplate.textRadius); //rotate方法旋转当前的绘图 ctx.rotate(angle + arc / 2 + Math.PI / 2); /** 下面代码根据奖品类型、奖品名称长度渲染不同效果，如字体、颜色、图片效果。(具体根据实际情况改变) **/ 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"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){//奖品名称长度超过一定范围 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{ //在画布上绘制填色的文本。文本的默认颜色是黑色 //measureText()方法返回包含一个对象，该对象包含以像素计的指定字体宽度 ctx.fillText(text, -ctx.measureText(text).width / 2, 0); } //添加对应图标 if(text.indexOf("闪币")>0){ var img= document.getElementById("shan-img"); img.onload=function(){ ctx.drawImage(img,-15,10); }; ctx.drawImage(img,-15,10); }else if(text.indexOf("谢谢参与")>=0){ var img= document.getElementById("sorry-img"); img.onload=function(){ ctx.drawImage(img,-15,10); }; ctx.drawImage(img,-15,10); } //把当前画布返回（调整）到上一个save()状态之前 ctx.restore(); //----绘制奖品结束---- } } } </script>引用jquery
在加载以下JS
/* "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 interface Wilq32=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 dependency jQuery(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") "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 IE this._container.appendChild(this._vimage); this._rootObj.appendChild(this._container); this._rootObj.style.position="relative"; // FIXES IE PROBLEM this._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); } else return 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 optimisation this._heightHalf=this._height/2;// used for optimisation var _widthMax=Math.sqrt((this._height)*(this._height) + (this._width) * (this._width)); this._widthAdd = _widthMax - this._width; this._heightAdd = _widthMax - this._height; // widthMax because maxWidth=maxHeight this._widthAddHalf=this._widthAdd/2; // used for optimisation this._heightAddHalf=this._heightAdd/2;// used for optimisation this._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 "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 canvas this._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 screen this._cnv.translate(this._widthHalf,this._heightHalf); // we move image back to its orginal this._cnv.rotate(angle); // rotate image this._cnv.translate(-this._widthHalf,-this._heightHalf); // move image to its center, so we can rotate around its center this._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);感兴趣的朋友可以使用在线HTML/CSS/JavaScript代码运行工具：http://tools.jb51.net/code/HtmlJsRun 测试上述代码运行效果。
更多关于JavaScript相关内容感兴趣的读者可查看本站专题：《JavaScript数学运算用法总结》、《JavaScript数据结构与算法技巧总结》、《JavaScript数组操作技巧总结》、《JavaScript排序算法总结》、《JavaScript遍历算法与技巧总结》、《JavaScript查找算法技巧总结》及《JavaScript错误与调试技巧总结》
希望本文所述对大家JavaScript程序设计有所帮助。
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