{ ... }
type
 TPolygon = array of TPoint;
procedure ZoomPolygon(var Polygon: TPolygon; const Center: TPoint; const Scale: Double);
var
 I: Integer;
begin
 for I := 0 to High(Polygon) do
 begin
  Polygon[I].X := Round(Scale * (Polygon[I].X - Center.X) + Center.X);
  Polygon[I].Y := Round(Scale * (Polygon[I].Y - Center.Y) + Center.Y);
 end;
end;