[Freeciv-Dev] Re: (PR#8619) AutoReply: Obscure Bug related to ISO coordinated and BORDER macro

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=8619 >

Marcelo Burda wrote:
> <URL: http://rt.freeciv.org/Ticket/Display.html?id=8619 >
> 
> Le jeu 29/04/2004 à 17:46, Jason Short a écrit :
> 
>><URL: http://rt.freeciv.org/Ticket/Display.html?id=8619 >
>>
>>Marcelo Burda wrote:
>>
>>><URL: http://rt.freeciv.org/Ticket/Display.html?id=8619 >
>>>
>>>MMM...
>>>DIR_DX, DIR_DY then DIRSTEP is not well defined in ISO coordinated!
>>> the adjc_iterate in smootmap no whell defined too
>>
>>DIR_DX/DIR_DY may only be used in map coordinates.  But why isn't it 
>>well defined?
> 
> in code make a DIRSTEP (in iterates) from map coordinated in the code of
> generator
> this call data from DIR_DX, DIR_DY
> if you work in map coordinates (ISO) and you want make a step to the E
> you need a DX=+1 and ad DY=-1 no the values DX=+1, DY=0 called by
> DIRSTEP for a step to N or S these is more complex you need to make a
> new mapstep, DIRSTEP is only to be used in natural coordinated

Hmm...

DIRSTEP only works in map coordinates.  And the directions are map 
directions.  So if you have an iso-map DIR8_EAST isn't east on the 
iso-map but east in the coordinate system.

This hasn't been a problem anywhere since nobody really hard-codes any 
specific directions.  Usually the callers just want to iterate over 
them.  However you could also have the concept of a native direction. 
But you can't do a DIRSTEP in native coordinates because the vector 
differs depending on where you are.  So you'd need something like


   bool native_mapstep(int *nat_x1, int *nat_y1, int nat_x, int nat_y,
                       enum direction8 nat_dir)
   {
     int map_x, map_y;
     enum direction8 map_dir;
     bool is_real;

     native_to_map_pos(&map_x, &map_y, nat_x, nat_y);
     native_to_map_dir(&map_dir, nat_dir);
     if (MAPSTEP(map_x, map_y, map_x, map_y, map_dir)) {
       map_to_native_pos(nat_x1, nat_y1, map_x, map_y);
       return TRUE;
     } else {
       return FALSE;
     }
   }

or maybe just

   MAPSTEP(map_x1, map_y1, map_x, map_y,
           native_to_map_dir(DIR8_EAST));

Finally note that natural coordinates aren't used anywhere.  But you 
could do a DIRSTEP in natural coordinates.  In this case east would be 
(ntl_x+2, ntl_y).

jason