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

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

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.οnlοad=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

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){//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

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.οnlοad=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.οnlοad=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----

}

}

}

引用jquery

在加载以下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

// 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

{

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

{

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

{

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") ? (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 dependency

jQuery(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 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 ? (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 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('');

};

} catch (e) {

return function (tagName) {

return document.createElement('');

};

}

})();

}

})(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。

希望本文所述对大家JavaScript程序设计有所帮助。