vml绘制凹凸多边形的判断

/**
*vml绘制多边形时判断多边形是否为凹或凸多边形
*finallyX,finallyY多边形最后一顶点的坐标;
*otherPointArray 一个存放着多边形的除最后顶点坐标(points)的数组
*/
//每点的坐标
funcotion points(x,y){
this.x=x;
this.y=y;
}
var circumscription= function(otherPointArray,finallyX,finallyY){

//工能：判断多边形是否符合条件只能绘制凹、凸的多边形
if(otherPointArray.length>2){
//判断两条线段是否有焦点
var Intersect1=function(L1,L2){
return( (Math.max(L1.pt1.x, L1.pt2.x) >= Math.min(L2.pt1.x, L2.pt2.x)) &&
(Math.max(L2.pt1.x, L2.pt2.x) >= Math.min(L1.pt1.x, L1.pt2.x)) &&
(Math.max(L1.pt1.y, L1.pt2.y) >= Math.min(L2.pt1.y, L2.pt2.y)) &&
(Math.max(L2.pt1.y, L2.pt2.y) >= Math.min(L1.pt1.y, L1.pt2.y)) &&
(Multiply(L2.pt1, L1.pt2, L1.pt1) * Multiply(L1.pt2, L2.pt2, L1.pt1) >= 0) &&
(Multiply(L1.pt1, L2.pt2, L2.pt1) * Multiply(L2.pt2, L1.pt2, L2.pt1) >= 0)
);
}
// 计算叉乘 |P0P1| × |P0P2|
var Multiply=function( p1,p2,p0){
return ( (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y) );
}
//焦点计数器
var count1=0;
for(var a=1;a<otherPointArray.length;a++){
//得到一条线的两个端点坐标
var px1=otherPointArray[a-1];
var px2=otherPointArray[a];

//起始点击点和最后点击点前一点击点的坐标
var px3=otherPointArray[0];
var px4=otherPointArray[otherPointArray.length-1];
//alert(px1+"  "+px2+"  "+downX+"  "+downY);
//获取多边形的一条边
var point1=new Point();
point1.x=px1.x;
point1.y=px1.y
var point2=new Point();
point2.x=px2.x;
point2.y=px2.y;
var line1=new LineSegment();
line1.pt1=point1;
line1.pt2=point2;
//获取多边形的最后两条边并判断它们和其他边的交点个数
for(var b=0;b<2;b++){
var point3=new Point();
var point4=new Point();
var line2=new LineSegment();
if(b==0){
point3.x=px3.x;
point3.y=px3.y;
}else{
point3.x=px4.x;
point3.y=px4.y;
}
point4.x=finallyX;
point4.y=finallyY;
line2.pt1=point3;
line2.pt2=point4;
if(Intersect1(line1,line2)){
++count1;
}
}
//如果多边形的最后两条边中的有一条和其它边有两个以上的交点就返回
if(count1>2){
alert("抱歉，多边形只能是凸多边形或凹多边形");
return true;
}
else{
//return false;
}
}
//return;
}
}