[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 04:47:46PM +0100, Gregory Berkolaiko wrote:
> > On Wed, 10 Apr 2002, Raimar Falke wrote:
> > 
> > > On Wed, Apr 10, 2002 at 12:14:44PM +0100, Gregory Berkolaiko wrote:
> > > > Read your latest path_finding3.h
> > > > Still not sure how get_next_path is supposed to be used?
> > > 
> > > You have the source and the destination. You pass the source to
> > > pf_get_map and the destination to pf_get_path_from_map. From
> > > pf_get_path_from_map you will get the path. After this you destroy the
> > > map.
> > 
> > Raimar, it would really help if you occasionally read the questions before 
> > writing the answer.  Please answer the original question.
> 
> Sorry I misread it. The example I posted makes it quite clear:
> 
>   map = pf_get_map(parameter);
>   do {
>      struct pf_path path;
> 
>      pf_get_next_path_from_map(map, &path);
> 
>      if(!path.found_a_valid) {
>        break;
>      }
> 
>      check_position_xy_for_something(LAST_POSITION(&path));
>   } while (position_is_relevant(path));
> 
>   pf_destroy_map(map);

either I am very confused or you propose to return the whole path to each 
new accessible destination but you don't use anything but the last 
position.  Doesn't make any sense to me...

> > > > Is it just very expensive version of my get_next_location?
> > 
> > And this one.  I mean: does get_next_path actually returns a path?
> 
> It does the same as get_next_location AFAI can say this at this
> point. Yes it returns the path from the start to the current
> position. So in essence:
>  get_next_location == LAST_POSITION(pf_get_next_path_from_map)

my worst fears confirmed.

> > > provide provide iterators not only for one step but also for multiple
> > > targets. Just thing of this example: you have a settler which want
> > > itself to add to some city. You have the start position and multiple
> > > destinations on the same continent. You don't have to calculate all
> > > costs to reach all tiles of the continent. You may use the simple
> > > iterator but pf_get_path_from_map will do this for you.
> > 
> > how will get_path do it?
> 
> pf_get_path_from_map is an optimized version of:
> 
>   forever:
>     path=pf_get_next_path_from_map
>     if !path.is_valid: 
>       return path
>     if LAST_POS(path) == destination:
>       return path

that doesn't answer the question.
do you propose to stuff a list of destinations into pf_get_path ?
or supply it with a is_final_destination callback?

I think just letting the "user" write the loop is much clearer and 
cheaper.  I tried it call-back way (terminating explorer search on 
discovering a hut), it didn't look pretty.

G.