function IsPointInTriangle(xa, ya, xb, yb, xc, yc, xd, yd: integer): boolean;
begin
  isPointInTriangle := abs((xa - xd) * (yb - yd) - (xb - xd) * (ya - yd)) +
                       abs((xa - xc) * (yd - yc) - (xd - xc) * (ya - yc)) +
                       abs((xd - xc) * (yb - yc) - (xb - xc) * (yd - yc)) =
                       abs((xa - xc) * (yb - yc) - (xb - xc) * (ya - yc))
end;