[Freeciv-Dev] Re: Map coordinate cleanups.

[Raimar Falke <hawk@xxxxxxxxxxxxxxxxxxxxxxx>]

On Sat, Aug 18, 2001 at 07:12:24PM -0700, Kevin Brown wrote:
> 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?

What topologies can be reprsented this way? How does they look like
with such "extra unreal" tiles? IMHO
  neighbour( neighbour(p, some_direction), reverse_direcion(some_direction)) == 
p
Since else you have problems displaing it.

        Raimar

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