[Freeciv-Dev] (PR#6721) A Quincuncial topology

["Marcelo Burda" <mburda@xxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=6721 >



> The formulas represent the simplest form of wrapping.  So with
> 
>    Y = -Y - 1
>    X = map.xsize - 1 - x
 yes

> we are mirroring Y around the origin and mirroring X around the
> map.xsize/2 axis.


We can make this in 2  mirroring but the end result is
 a rotation of 180°. the cenetral point of ratation is in this example
at point { X_C=map.xsize/2 - 0.5, Y_C= -0.5 } for a even xsize .This code 
 assume the sides size are even numbers (TODO not alow odd ones!) it is
 a Central Symetrie.

more exact if we call it a central symetrie wraping (but it can afraids some 
ones)
 
then   Y = -Y - 1 is a mirroring around the axes definde by Y=Y_C and
 X = map.xsize - 1 - X is a mirroring around the axes defined by X=X_C;