js抽奖转盘实现方法分析

<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。