Code review comment for lp:~miroslavr256/widelands/bug-1550568-restool_undo_crash

@tiborb95

> So if I understand it properly, even if the resource is not changed on particular field (like
> setting coal on grass), old (=new) resource is saved somewhere and when doing undo it is re-set
> (=replacing the resource with the very same resource).

Yes, that's right.

> I have performance in my mind. When I work on big maps it is real pain and editor lags very badly...

I didn't really consider performance implications. My guess would be that the overlay update function is mostly at fault. Anyway, could you try this patch and see how it is performance-wise: http://pastie.org/private/cf2coofqafpffzm2h5ra ? This should skip unnecessary fields and still not crash the game after undoing the action.