javascript+canvas实现刮刮卡抽奖效果

运用canvas做的简单刮刮卡效果，每次刷新可重新测试

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
<style type="text/css">
 *{ margin:0; padding:0;} 

.cjbox{ margin:100px; height:80px; width:200px; background:#FFF; position:relative;}
#canvas{position:absolute; left:0px; top:0px;z-index:99;}
.sjmes{ position:absolute; left:0px; top:0px; height:80px; width:200px; text-align:center; font-size:40px; line-height:80px; z-index:9;}
</style>
<title>demo1</title>
</head>
<body> 

<div style="position:relative; margin:20px 100px; background:#0CF; height:400px; width:500px; margin:0 auto;">
  <div>刮刮卡简单抽奖</div>
  <div class="cjbox">
    <div class="sjmes" id="sjmes"></div>
    <canvas width=200 height=80 id="canvas"></canvas>
  </div>
</div> 

</body>
<script type="text/javascript">
//init
var cjcon=["一等奖","二等奖","三等奖","谢谢参与"];//奖项设置
var cjper=[3,10,20,100];//奖项率，次数
/*
 * sjmes
 * @Author 透笔度（1530341234@qq.com）
 * @param {cjcon}   所有奖项
 */
var percjcon=[];
for(var i=0;i<cjper.length;i++){
  peic(cjper[i],i);
};
function peic(len,ind){
  for(var i=0;i<len;i++){
    percjcon.push(cjcon[ind]);
  };
};
var sjmes = document.getElementById("sjmes");
var numrandom=Math.floor(Math.random()*percjcon.length);
sjmes.innerHTML=percjcon[numrandom];

var opacityb=0.5;//透明百分比,参考值,什么程度出现提示
var backcolorb="#ffaaaa";
var numl=200*80;//总像素个数
var nump;//出现backcolorb的个数
var opacitya;//透明百分比实际值

var canvas = document.getElementById("canvas"); //获取canvas
var context = canvas.getContext('2d'); //canvas追加2d画图
var flag = 0; //标志，判断是按下后移动还是未按下移动 重要
var penwidth=20; //画笔宽度
context.fillStyle="#faa"; //填充的颜色
context.fillRect(0,0,200,80); //填充颜色 x y坐标 宽 高

canvas.addEventListener('mousemove', onMouseMove, false); //鼠标移动事件
canvas.addEventListener('mousedown', onMouseDown, false); //鼠标按下事件
canvas.addEventListener('mouseup', onMouseUp, false); //鼠标抬起事件
var movex=-1;
var movey=-1;
var imgData;//imagedada容器
var rgbabox=[];//存放读取后的rgba数据；
function onMouseMove(evt) {
  if (flag == 1) {
    movex=evt.layerX;
    movey=evt.layerY;
    context.fillStyle="#FF0000";
    context.beginPath();
    context.globalCompositeOperation="destination-out";
    context.arc(movex,movey,penwidth,0,Math.PI*2,true); //Math.PI*2是JS计算方法，是圆
    context.closePath();
    context.fill();
  }
}
function onMouseDown(evt) {
 flag = 1; //标志按下
}
function onMouseUp(evt) {
  flag = 0;
  //读取像素数据
  imgData=context.getImageData(0,0,200,80);//获取当前画布数据
  //imgData.data.length 获取图片数据总长度，没4个为一组存放rgba
  for(var i=0; i<imgData.data.length;i+=4){
    var rval=imgData.data[i];
    var gval=imgData.data[i+1];
    var bval=imgData.data[i+2];
    var aval=imgData.data[i+3];
    var rgbaval=rval+"-"+gval+"-"+bval+"-"+aval;
    rgbabox.push(rgbaval);
  }
  //end
  for(var j=0;j<rgbabox.length;j++){
    //alert(rgbabox[j].split("-")[0])
    rgbabox[j]='#'+rgbToHex(rgbabox[j].split("-")[0],rgbabox[j].split("-")[1],rgbabox[j].split("-")[2]);
  }
  nump=countSubstr(rgbabox.join(","),backcolorb,true);
  opacitya=(numl-nump)/numl;
  if(opacitya>opacityb){
    alert("恭喜你获得"+percjcon[numrandom])
  }else{}

}
function rgbToHex(r, g, b) { return ((r << 16) | (g << 8) | b).toString(16); }//rgb转为16进制 #xxx形式
function countSubstr(str,substr,isIgnore){//计算字符串出现子字符串的个数
  var count;
  var reg="";
  if(isIgnore==true){
  reg="/"+substr+"/gi";
  }else{
  reg="/"+substr+"/g";
  }
  reg=eval(reg);
  if(str.match(reg)==null){
  count=0;
  }else{
  count=str.match(reg).length;
  }
  return count;
}
//end
</script>
</html>

以上所述就是本文的全部内容了，希望大家能够喜欢。