[Freeciv-Dev] Re: [RFC] Move cost map interface

[Raimar Falke <hawk@xxxxxxxxxxxxxxxxxxxxxxx>]

On Mon, Apr 15, 2002 at 08:20:59PM +0100, Gregory Berkolaiko wrote:
> On Mon, 15 Apr 2002, Raimar Falke wrote:
> 
> > On Mon, Apr 15, 2002 at 06:15:29PM +0100, Gregory Berkolaiko wrote:
> > > On Mon, 15 Apr 2002, Raimar Falke wrote:
> > > 
> > > > > > It is just not part of the interface. And pf_map will get bigger. 
> > > > > > You
> > > > > > need for example a way to cache the per tile extra cost, the per 
> > > > > > tile
> > > > > > zoc value and so on. And if pf_position is public you can't store it
> > > > > > in pf_position.
> > > > > 
> > > > > These are the things you can add later.  We should at least sketch 
> > > > > the 
> > > > > implementation.
> > > > 
> > > > We have a sketch in our heads and in gotohand and goto_agent. But this
> > > > isn't important.
> > > 
> > > We are now tying to design something which is fast and easy-to-use.
> > > And the need to make it fast will inevitably show on the face 
> > > (inter-face).  
> > 
> > > This is why I wanted to hide pf_position: we need to decide what is
> > > the best implementation from the performace point of view.  So
> > > please repeat you reasons why pf_position should be made public.
> > 
> > IMHO it is better to provide the data in a struct than to provide 2-3
> > functions which provide the data. From the performance point of view
> > and also for clarity
> > 
> > > I actually think we should use Ross's warmap.c as the prototype.
> > 
> > If we have an interface everybody may provide an implementation. Which
> > one goes is will depend on performance, code readability and
> > correctness.
> 
> Okay, let me say it out loud: I don't really care what path struct will 
> look like and what information it will provide.  What I care about is 
> pf_get_next_position and the value it returns.  It should return some sort 
> of pointer into some sort of internal cost(war)map element using which 
> one can extract the coordinates of the next location and the relevant 
> costs.
> 
> If the implementation will be performace-orientated, this structure will 
> not look like pf_position as you've defined it.  Therefore the second 
> agrument to pf_get_next_position will not be struct pf_position *, but
> struct pf_location * or even an int *.
> 
> Thus we have a separation: pf_position is a member of path and pf_location 
> (or whatever it will be called) is the map element (containing minimum 
> info) to be used by the map-generation internals.  
> 
> The functions I'm interested in will look like this:
>       pf_location pf_get_next_position(pf_map_t map);
> and
>       void pf_construct_path(pf_map_t map, const pf_location,
>                                struct pf_path *path);
> with pf_location being some type which will emerge during implementation 
> development.  BTW, I'm not terribly interested in pf_construct_path 
> either, but I thought we should have it for some future uses might emerge.
> 
> If we agree on that, then I have no other qualms about the path_finding6.h
> (maybe some more minor corrections will emerge on contents of 
> pf_parameter but I don't see anything now).  Probably this is what you 
> originally had in mind...

Then please tell me how do you extract the x and y from the int *? You
have to extract these to be able to test the exit condition. Either
you will construct the whole path (which you don't want to do) or you
get x and y from pf_get_next_position.

I have also thought about a seperate struct as return value of
pf_get_next_position. But pf_position can handle it quite well. So we
use only parts of the struct. 

But I have no great problems if you want another struct. Should this
just be a stripped down version of pf_position (x,y, moves_left)? Or
something which is determined by the implementation? But remember x
and y have to be accessible. So you can't really make the struct
private.

        Raimar


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