手机刮刮乐HTML5代码

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手机刮刮乐HTML5代码,
使用原型prototype扩展了一个clearArc 清除圆内像素的功能,
此功能未完成扇形清除功能,
此外,在清除圆内的像素时,还有点瑕疵,右边和下边还不够圆滑,有明显的齿状。如果你找到修复方法请一定要告诉我哟。不过此清除方法用于刮刮乐已经完全满足需求了
 
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>刮刮乐</title>
<script type="text/javascript">
  window.onload = function() {
    init();
  }
  CanvasRenderingContext2D.prototype.clearArc=function(x,y,radius,startAngle, endAngle, counterclockwise){
    var distance = function(x0,y0,x1,y1){
      var dis = Math.sqrt(Math.pow(x0-x1,2)+Math.pow(y0-y1,2));
      //return Math.ceil(dis*10000)/10000;
      return Math.round(dis*10000)/10000;
    };
    //首先获得矩形
    var diameter = radius*2;
    var startX = x-radius;
    var cx = radius-(0-startX);
    startX = startX<0?0:startX;
    cx = cx-startX;
    var startY = y-radius;
    var cy = radius-(0-startY);
    startY = startY<0?0:startY;
    cy = cy-startY;
    var imgData = this.getImageData(startX,startY,diameter,diameter);//需要处理的矩形
    for (var i=0;i<imgData.data.length;i+=4){
      //矩阵内的坐标
      var ii = i/4;
      var ix = Math.floor(ii/imgData.width);
      var iy = ii%imgData.height;
      var dis = distance(ix,iy,cx,cy);
      if(dis<=radius){//此点在圆内
        imgData.data[i+0]=0;
        imgData.data[i+1]=0;
        imgData.data[i+2]=0;
        imgData.data[i+3]=0;
        continue;
      }
      var dr = dis-radius;
      if(dr<Math.SQRT2){
        var n = Math.sqrt(Math.pow(dr, 2)/2)*256;//新
        var o = imgData.data[i+3];
        imgData.data[i+3]=n<o?n:o;
        continue;
      }
    }
    this.putImageData(imgData,startX,startY);
  };
  function init() {
    var imageWidth = 200;
    var imageHeight = 100;
    var gglc = document.getElementById("gglc");
    var gglc2D = gglc.getContext("2d");
    gglc2D.fillStyle = '#cccccc'; //设置覆盖层的颜色
    gglc2D.fillRect(1, 1, imageWidth, imageHeight); //设置覆盖的区域
    //gglc2D.clearArc(25,25,20);
    gglc.addEventListener("touchmove", function(event) {
      event.preventDefault();
      for(var i in event.targetTouches){
        var touch = event.targetTouches[i];
        gglc2D.clearArc(touch.pageX,touch.pageY,20);
      }
    }, false);
    gglc.addEventListener("touchstart", function(event) {
      event.preventDefault();
      for(var i in event.targetTouches){
        var touch = event.targetTouches[i];
        gglc2D.clearArc(touch.pageX,touch.pageY,20);
      }
    }, false);
  }
</script>
</head>
<body>
  <div style="position: relative; width: 100%;height: 100%;">
    <div style="position: absolute; width: 200px; height: 100px; text-align: center;line-height: 100px;border: 1px solid #ccc;'">谢谢惠顾</div>
    <canvas style="position: absolute;" id="gglc" width="201" height="101"></canvas>
  </div>
</body>
</html>