function  PtInRgn(TestPolygon :  array   of  TPoint;  const  P : TPoint): boolean;
  var 
   ToTheLeftofPoint, ToTheRightofPoint : byte;
   np : integer;
   OpenPolygon : boolean;
   XIntersection : real;
  begin 
   ToTheLeftofPoint :=  0 ;
   ToTheRightofPoint :=  0 ;
   OpenPolygon := False;

    {Prufen ob das Polygon geschlossen ist} 
    {tests if the polygon is closed} 

    if   not  ((TestPolygon[ 0 ].X = TestPolygon[High(TestPolygon)].X)  and 
     (TestPolygon[ 0 ].Y = TestPolygon[High(TestPolygon)].Y))  then 
     OpenPolygon := True;

    {Tests fur jedes Paar der Punkte, um zu sehen wenn die Seite zwischen 
   ihnen, die horizontale Linie schneidet, die TestPoint durchlauft} 
    {tests for each couple of points to see if the side between them 
   crosses the horizontal line going through TestPoint} 

    for  np :=  1   to  High(TestPolygon)  do 
      if  ((TestPolygon[np -  1 ].Y <= P.Y)  and 
       (TestPolygon[np].Y > P.Y))  or 
       ((TestPolygon[np -  1 ].Y > P.Y)  and 
       (TestPolygon[np].Y <= P.Y))
        {Wenn es so ist}      {if it does} 
        then 
      begin 
        {berechnet die x Koordinate des Schnitts} 
        {computes the x coordinate of the intersection} 

       XIntersection := TestPolygon[np -  1 ].X +
         ((TestPolygon[np].X - TestPolygon[np -  1 ].X) /
         (TestPolygon[np].Y - TestPolygon[np -  1 ].Y)) * (P.Y - TestPolygon[np -  1 ].Y);

        {Zahler entsprechend verringern} 
        {increments appropriate counter} 
        if  XIntersection < P.X  then  Inc(ToTheLeftofPoint);
        if  XIntersection > P.X  then  Inc(ToTheRightofPoint);
      end ;

    {Falls das Polygon offen ist, die letzte Seite testen} 
    {if the polygon is open, test for the last side} 

    if  OpenPolygon  then 
    begin 
     np := High(TestPolygon);   {Thanks to William Boyd - 03/06/2001} 
      if  ((TestPolygon[np].Y <= P.Y)  and 
       (TestPolygon[ 0 ].Y > P.Y))  or 
       ((TestPolygon[np].Y > P.Y)  and 
       (TestPolygon[ 0 ].Y <= P.Y))  then 
      begin 
       XIntersection := TestPolygon[np].X +
         ((TestPolygon[ 0 ].X - TestPolygon[np].X) /
         (TestPolygon[ 0 ].Y - TestPolygon[np].Y)) * (P.Y - TestPolygon[np].Y);

        if  XIntersection < P.X  then  Inc(ToTheLeftofPoint);
        if  XIntersection > P.X  then  Inc(ToTheRightofPoint);
      end ;
    end ;

    if  (ToTheLeftofPoint  mod   2  =  1 )  and  (ToTheRightofPoint  mod   2  =  1 )  then  Result := True
    else 
     Result := False;
  end ;  {PtInRgn}