what is the meaning of the tag "ww,wv" in portal?

Hello,

<ww> and <wv> are used to define "space warping" portals. Few people know about those...
Since your question is interesting and deserves an answer, I asked on the IRC channel (#crystalspace @ chat.freenode.net)
Here's the discussion which I hope will help you using portals...
Hopefully Jorrit will reply in this thread, giving a definite answer

<vknecht> anyone good with space warping portals ?

<thebolt> no
<thebolt> thats an impossible combination Wink

<vknecht> perhaps you're not good, but know the basis ?
<Xordan> Nobody in the world undecided

<thebolt> vknecht: yea, i think i do at least
<vknecht> there are 2 vectors involved in warping ? "before" and "after" ?
<vknecht> http://rafb.net/p/whOtS540.html
<thebolt> yea, technically only one vector is needed, but two makes it a bit easier to specify "by hand"
<vknecht> I guess ww is the optional one ?
<thebolt> technically at least either is optional ,)
<vknecht> mmm, ok
<thebolt> but that before=after is a bit suspicious.. not 100% sure what its supposed to do
<vknecht> the x, y, and z given to ww and/or wv are absolute coords, the destination position in destination sector ?
<thebolt> no
<thebolt> say you have a point in sector A (which i think is the target sector)
<thebolt> call its coordinate P
<thebolt> then to get the position in another sector you offset it by before (ww), rotate by the matrix and then offset result with after (wv?)
<thebolt> so P' = wv + M*(P+ww)
<thebolt> or i think thats how its defined
<thebolt> internally its moved around so you only store one vector + matrix
<thebolt> (the expression above can be rewritten as P' = (wv + M*ww) + M*P ..)
<vknecht> I see in flarge that some portals don't have a matrix; what does it mean ? identity matrix or 0 is used ? (incidentally, it seems that those which have no matrix don't set wv)
<thebolt> identity
<thebolt> so no rotation
<thebolt> and if you ahve no rotation then there is no need to specify both ww and wv
<vknecht> ok