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}