本文例項講述了js抽獎轉盤實現方法。分享給大家供大家參考，具體如下：

HTML 這裡.left 固定了圓的寬度和高度，還有canvas也設定了固定寬高 繪製圓心的座標也就出來了 (203,203)

抽獎轉盤是由一個大圓和一個內圓完成 ；大圓負責繪製上獎品 ，內圓負責確定指標的位置，指標直接使用圖片，決定位置確定

<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="sp2/point.png"/>
</div>

</div>

外圓留空多少的問題

PS裡檢視間距是多少，此處圓心(203,203) 大圓的半徑就是203-10 =193

這個數值在下圖裡設定

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(){
      //動態新增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"];


      var rotateTimeOut = function (){
        $('#wheelcanvas').rotate({
          angle:0,animateTo:2160,duration:8000,callback:function (){
            alert('網路超時，請檢查您的網路設定！');
          }
        });
      };

      //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,callback:function (){
            alert(txt);
            turnplate.bRotate = !turnplate.bRotate;
          }
        });
      };

      $('.pointer').click(function (){
        if(turnplate.bRotate)return;
        turnplate.bRotate = !turnplate.bRotate;
        //獲取隨機數(獎品個數範圍內)
        var item = rnd(1,turnplate.restaraunts.length);
        //獎品數量等於10,指標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;

    }


    //頁面所有元素載入完畢後執行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2
        var ctx = canvas.getContext("2d");
        //在給定矩形內清空一個矩形
        ctx.clearRect(0,422,422);
        //strokeStyle 屬性設定或返回用於筆觸的顏色、漸變或模式
        ctx.strokeStyle = "#FFBE04";
        //font 屬性設定或返回畫布上文字內容的當前字型屬性
        ctx.font = '16px Microsoft YaHei';
        // 繪製圓 （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,繪製方向) 方法建立弧/曲線（用於建立圓或部分圓）
          ctx.arc(203,203,turnplate.outsideRadius,angle,angle + arc,false);//繪製外圓
          ctx.arc(203,turnplate.insideRadius,true);//繪製內圓
          ctx.stroke();
          ctx.fill();
          //鎖畫布(為了儲存之前的畫布狀態)
          ctx.save();

          //----繪製獎品開始----
          ctx.fillStyle = "#FFF";/*獎品文字顏色*/
          var text = turnplate.restaraunts[i];
          var line_height = 17;
          //translate方法重新對映畫布上的 (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);

          /** 下面程式碼根據獎品型別、獎品名稱長度渲染不同效果，如字型、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範圍
            text = text.substring(0,6)+"||"+text.substring(6);
            var texts = text.split("||");
            for(var j = 0; j<texts.length; j++){
              ctx.fillText(texts[j],j * line_height);
            }
          }else{
            //在畫布上繪製填色的文字。文字的預設顏色是黑色
            //measureText()方法返回包含一個物件，該物件包含以畫素計的指定字型寬度
            ctx.fillText(text,-ctx.measureText(text).width / 2,0);
          }

          //新增對應圖示
          if(text.indexOf("閃幣")>0){
            var img= document.getElementById("shan-img");
            img.onload=function(){
              ctx.drawImage(img,-15,10);
            };
            ctx.drawImage(img,10);
          }else if(text.indexOf("謝謝參與")>=0){
            var img= document.getElementById("sorry-img");
            img.onload=function(){
              ctx.drawImage(img,10);
          }
          //把當前畫布返回（調整）到上一個save()狀態之前
          ctx.restore();
          //----繪製獎品結束----
        }
      }
    }

  </script>

引用jquery

在載入以下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 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);							// 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線上HTML/CSS/JavaScript程式碼執行工具：http://tools.jb51.net/code/HtmlJsRun 測試上述程式碼執行效果。

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希望本文所述對大家JavaScript程式設計有所幫助。