判断点和多边形的位置关系

#include <afx.h>
#include <math.h>

#define _SnapSame(x1, x2, lfSnap)        (0==lfSnap?x1==x2:fabs(x1-x2)<lfSnap)
#define _SnapLarge(x1, x2, lfSnap)        (x1>x2-lfSnap)
#define _SnapLarge2(x1, x2, lfSnap)        (x1>x2+lfSnap)

//-1在外面，0在上面，1在里面
int PtInRegionEx(double x, double y, double *pX, double *pY, int nSum, double lfSnap)
{
    if (nSum <= 0 || NULL == pX || NULL == pY)
    {
        return FALSE;
    }
    int i0,i1,i2, ret=0;
    double xmin1, xmax1, ymin1, ymax1;
    for( int i=0; i<nSum; i++ )
    {
        i0 = i;
        i1 = (i0+1)%nSum;
        if( _SnapSame( pX[i0],x,lfSnap ) && _SnapSame( pY[i0],y,lfSnap ) )
            return 0;

        if( pX[i0]<pX[i1] ){ xmin1 = pX[i0]; xmax1 = pX[i1]; }
        else { xmin1 = pX[i1]; xmax1 = pX[i0]; }
        if( pY[i0]<pY[i1] ){ ymin1 = pY[i0]; ymax1 = pY[i1]; }
        else { ymin1 = pY[i1]; ymax1 = pY[i0]; }
        //        if( y<ymin1 || y>ymax1 || x>xmax1 )continue;
        if( _SnapLarge2(ymin1,y,lfSnap) || _SnapLarge2(y,ymax1,lfSnap) || _SnapLarge2(x,xmax1,lfSnap) )
            continue;

        if( pY[i1] == pY[i0] )
            //        if( _SnapSame(pY[i1],pY[i0],lfSnap) )
        {
            //            if( pY[i0]==y )
            if( _SnapSame(pY[i0],y,lfSnap) )
            {
                //                if( ( pX[i0]>x && pX[i1]<x ) ||
                //                    ( pX[i0]<x && pX[i1]>x ) )
                if( ( _SnapLarge(pX[i0],x,lfSnap) && _SnapLarge(x,pX[i1],lfSnap) ) ||
                    ( _SnapLarge(x,pX[i0],lfSnap) && _SnapLarge(pX[i1],x,lfSnap) ) )
                    return 0;
            }
        }
        //        if( y==ymin1 || y==ymax1 )
        else if( _SnapSame(y,ymin1,lfSnap) || _SnapSame(y,ymax1,lfSnap) )
        {
            if(_SnapSame(y,ymin1,lfSnap) && _SnapSame(y,ymax1,lfSnap)&&
                (( _SnapLarge(pX[i0],x,lfSnap) && _SnapLarge(x,pX[i1],lfSnap) ) ||
                ( _SnapLarge(x,pX[i0],lfSnap) && _SnapLarge(pX[i1],x,lfSnap) )))
            {
                return 0;
            }
            //            if( y==pY[i0] && x<pX[i0] )
            if( _SnapSame(y,pY[i0],lfSnap) && _SnapLarge(pX[i0],x,lfSnap) )
            {
                i2 = i0;
                while( true )
                {
                    i2 = (i2-1+nSum)%nSum;
                    if( pY[i2] == pY[i0] )
                    {
                        if( i2 == i1 || i2 == i0 )break;
                        continue;
                    }
                    //                    if( ( pY[i2]<y && pY[i1]>y ) ||
                    //                        ( pY[i2]>y && pY[i1]<y ) )
                    if( ( _SnapLarge(y,pY[i2],lfSnap) && _SnapLarge(pY[i1],y,lfSnap) ) ||
                        ( _SnapLarge(pY[i2],y,lfSnap) && _SnapLarge(y,pY[i1],lfSnap) ) )
                    {
                        ret ++;
                    }
                    break;
                }
            }
        }
        //        else if( x==xmin1 || x==xmax1 )
        else if( _SnapSame(x,xmin1,lfSnap) || _SnapSame(x,xmax1,lfSnap))
        {
            if(_SnapSame(x,xmin1,lfSnap) && _SnapSame(x,xmax1,lfSnap)&&
                (( _SnapLarge(y,pY[i0],lfSnap) && _SnapLarge(pY[i1],y,lfSnap) ) ||
                ( _SnapLarge(pY[i0],y,lfSnap) && _SnapLarge(y,pY[i1],lfSnap) )))
            {
                return 0;
            }
            //            if( x==xmin1 )
            if( _SnapSame(x,xmin1,lfSnap) )
            {
                ret ++;
            }
        }
        //        if( x<xmin1 )ret++;
        else if( _SnapLarge(xmin1,x,lfSnap) )
            ret ++;
        else
        {
            xmax1 = (y-pY[i0])*(pX[i1]-pX[i0])/(pY[i1]-pY[i0])+pX[i0];
            //            if( x==xmax1 )return 0;
            if( _SnapSame(x,xmax1,lfSnap) )return 0;
            //            if( x<xmax1 )ret++;
            if( _SnapLarge(xmax1,x,lfSnap) )ret ++;
        }
    }
    return 1==ret%2? 1:-1;
}