判断点在多边形内Javascript代码

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Javascript

JavaScript HTML

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gbk">
<title>img usemap属性</title>
</head>
<script>

function isPointInLine(point,linePoint1,linePoint2)
{
   //是否一个点向x轴的射线穿透线段,有交点
   var maxY=(linePoint1.y>linePoint2.y)?linePoint1.y:linePoint2.y;
   var minY=(linePoint1.y<linePoint2.y)?linePoint1.y:linePoint2.y;
   //alert("maxY" + maxY);
   //alert("minY = " + minY);
   var re=false;
   if(point.y<maxY && point.y>=minY)
   {
       a1 = point.x;
       a2 = (linePoint2.x-linePoint1.x)*(point.y-linePoint1.y)/(linePoint2.y-linePoint1.y);
       //alert(a1);
       //alert(a2);
       //alert(a1 <= a2);
       if(parseFloat(point.x) <= parseFloat(( linePoint1.x+(linePoint2.x-linePoint1.x)*(point.y-linePoint1.y)/(linePoint2.y-linePoint1.y) )) )
       {
       re=true;
       }
   }
   //alert("point :" + point.x + ":" + point.y + ";")
   //alert("linePoint1 :" + linePoint1.x + ":" + linePoint1.y + ";")
   //alert("linePoint2 :" + linePoint2.x + ":" + linePoint2.y + ";")
   //alert(re);
   return(re);
}

function isPointInPolygon(point,poly)
{
   //是否点在多边形里
   var crossNum=0;
   var re=true;
   for(var i=0;i<poly.length-1;i++)
   {
       if(isPointInLine(point,poly[i],poly[i+1]))
       {
           crossNum++;
       }
   }

   if((crossNum % 2)==0)
   {
       re=false;
   }

   return(re);
}

function clickme()
{
   var pa = document.getElementById("point").value.split(",");
   var p = {x:pa[0],y:pa[1]};

   var poa = document.getElementById("poly").value.split(",");
   var po = new Array();
   for(var i=0;i<poa.length/2;i++){
       po[i]={x:poa[2*i],y:poa[2*i+1]};
   };
   //for(var i=0;i<po.length;i++)
   //{
   //   alert(po[i].x);
   //   alert(po[i].y);
   //}

   //alert(p.x);
   //alert(p.y);

   alert(isPointInPolygon(p,po));
}
</script>

<body>
   原理：从要判断的点向x轴发射一条射线，如果射线与多边形的边有偶数次相交，那么点不在多边形内；奇数次相交，那么点在多边形内
   <br>
<input type="text" id="point" value="0.5,0.49" />点的横竖坐标，用逗号分隔
<br>
<input type="text" id="poly" value="0,0,0.75,0.75,1,0,1,1,0,1" />按照逆时针方向多边形点的横竖坐标坐标0
<input type="button" id="btn" value="点击我" onclick="clickme();">
</body>
</html>

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2010-08-20 15:51
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