[Freeciv-Dev] Re: Map coordinate cleanups.

[Kevin Brown <kevin@xxxxxxxxxxxxxx>]

Trent Piepho <xyzzy@xxxxxxxxxxxxx> wrote:
> On Sat, 18 Aug 2001, Gregory Berkolaiko wrote:
> > > You have basically understood everything.  The only thing that I have
> > > to add is this: normalization is independent of realness.
> > 
> > IS_WRAPPED = wrapping rules applied but not necessarily real
> 
> 
> As others (Ross?  David?) have pointed out, the purpose of wrapping
> coordinates is to discover which real tile they refer to.  If coordinates
> do not refer to a real tile, then they cannot be wrapped in a meaningful way. 
> It might appear that if you wrap the X coordinate around and leave the Y the
> same, you have wrapped a non-real coordinate, but that's just an illusion.
> 
> 
> Consider a diamond shaped map that's supposed to play like a sphere:
> 
> X    0  1  2  3  4
> Y
>           +--+
> 0         |  |
>        +--+--+--+
> 1      |  |  |  |
>     +--+--+--+--+--+
> 2   |  |  |  |  |  |
>     +--+--+--+--+--+
> 3      |  |  |  |
>        +--+--+--+  
> 4         |  |
>           +--+    
> 
> Coordinates wrap around the east and west edges, but not the north
> and south.  For example, (0,1) would wrap around the edge to (3,1),
> and (-1,2) would wrap to (4,2).  What would the coordinate (4, -1)
> wrap to?  Since it's a not a real coordinate, there is no meaningful
> way to wrap it.  The cylinder topology just creates the illusion
> that it is possible to wrap non-real coordinates.

This gives me an interesting idea.  I haven't really looked, so if
it's already implemented then slap me.  But:

If we set up the code so that you can define a map with intentionally
"unreal" locations (with such a location represented, say, by a space
character), then you should be able to get all sorts of interesting
topologies (well, crude approximations of them, anyway) out of it with
relatively simple wrapping rules.  Maybe.  I'm trying to come up with
a simple way of going from real tile to real tile when wrapping
through unreal tiles and which behaves as you'd intuitively expect
(more or less).  Going N/S/E/W is easy, I think: you wrap around that
direction until you hit a real tile, and that's where you land.  The
question is what to do for diagonal moves, and I haven't figured out
that one yet.  I'm tempted to say you should move to the unreal tile
then move in one component direction (e.g., N or E if the move was NE)
until you hit a real tile.  The component direction you use is
whichever gets you onto a real tile in the shortest map distance (so
unreal tiles count for the distance) in the component direction, or a
preferred component direction if they're equidistant".  But I'm not
sure how well that would really work.


Hmm...maybe this isn't such a good idea after all.  :-(   What do you
guys think?



-- 
Kevin Brown                                           kevin@xxxxxxxxxxxxxx

    It's really hard to define what "unexpected behavior" means when you're
                       talking about Windows.