[Freeciv-Dev] Re: [RFC] Path finding interface

[Gregory Berkolaiko <Gregory.Berkolaiko@xxxxxxxxxxxx>]

On Wed, 10 Apr 2002, Raimar Falke wrote:
> On Wed, Apr 10, 2002 at 11:38:55AM +0100, Gregory Berkolaiko wrote:
> > 
> > Yes, I thought about it, you are right.
> > The "special" scenarios I had in mind are:
> > 1. Finding the best route for a road from A to B:
> > first minimize the length of the future road (equiv to BMC being igter), 
> > than minimize over additional cost arising from the time required to build 
> > the road.
> > 2. Finding the shortest and safest path for a trireme (see anxious trireme 
> > bug):
> > first minimize over the lengths of all "safe" paths (the path is "safe" if 
> > the unit ends its move next to the shore),
> > than among these paths find the one which sticks to shore most of the time 
> > (in case the trireme has to end the move early).
> > Looking for safe paths would involve returning PF_IGNORE_COST as the 
> > additional cost for the path which would end the turn away from shore.
> 
> An extra callback
>  bool (*wait_test)(int x, int y, void *user_data);
> which tells the core that the unit should wait a turn?

no, too complicated.  What do you do inside wait_test?

imagine: trireme is at point A, needs to go to B, the only path 
A -> D2 -> D1 -> B (three moves, both Ds are dangerous).  You start with 
only 2 moves.

One solution is to push the current point into the queue twice, with cost 
0 (corresponding to setting off at once) and with cost 2 (corresponding to 
waiting for 2 moves).

The problem is, as before, the randomness of movement across terrain.  
It'd be ok with triremes, but not with land units.

> > This leads to the problem which is hardest to solve IMO:
> > 3. Take into account the possibility to end move early to stay out of 
> > trouble.
> > 
> > This would be very useful for military unit too.
> 
> We can declare a special return value (2*FC_INFINITY) of the callback
> which will abort the calculation. And you may also use wait_test.

abortion is not a solution in this case