function IsPointInLine(x1, y1, x2, y2 : integer; P : TPoint) : boolean;
var m: double;
    a: double;
begin
    m := sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
    if m = 0 then begin Result := false; exit; end;
    a := ((P.x - x1) * (x2 - x1) + (P.y - y1) * (y2 - y1)) /
    (sqrt((P.x - x1)*(P.x - x1) + (P.y - y1)*(P.y - y1)) *
        m);
    if ((sin(arccos(a)) * m) <= MinDistance) and
        Between(x1 - MinDistance, x2 + MinDistance, P.x) and
        Between(y1 - MinDistance, y2 + MinDistance, P.y)
     then
                Result := true
    else
                Result := false;
end;