[xmonad] darcs patch: Column layout

[Adam Vogt]

Hello Ilya,

I have a couple small suggestions inline below, send another patch fixing 
these things, and I'll apply it:

* On Saturday, June 06 2009, portnov wrote:

[..]

>+-- $usage
>+-- This module defines layot named Column. It places all windows in one

s/layot/layout/

>+-- column. Windows heights are calculated from equation: H1/H2 = H2/H3 = ... =
>+-- q, where `q' is given (thus, windows heights are members of geometric
>+-- progression). With Shrink/Expand messages one can change the `q' value.
[..]
>+columnMessage :: Column a -> SomeMessage -> Maybe (Column a)
>+columnMessage (Column q) m = fmap resize (fromMessage m)
>+    where resize Shrink = Column (q-0.1)
>+          resize Expand = Column (q+0.1)

Perhaps the 0.1 should be an additional parameter to Column? In many cases 
I noticed that the step between Expand messages was too small.

>+columnLayout :: Column a -> Rectangle -> W.Stack a -> [(a,Rectangle)]
>+columnLayout (Column q) rect stack = zip ws rects
>+    where ws = W.integrate stack
>+          n = length ws
>+          heights = map (xn n rect q) [1..n]
>+          ys = [fromIntegral $ sum $ take k heights | k <- [0..n-1]]
>+          rects = map (mkRect rect) $ zip heights ys
>+
>+mkRect :: Rectangle -> (Dimension,Position) -> Rectangle
>+mkRect (Rectangle xs ys ws _) (h,y) = Rectangle xs (ys+fromIntegral y) ws h
>+        
>+xn :: Int -> Rectangle -> Float -> Int -> Dimension
>+xn n (Rectangle _ _ _ h) q k = if q==1 then 
>+                                  h `div` (fromIntegral n)
>+                               else 
>+                                  round ((fromIntegral h)*q^(n-k)*(1-q)/(1-q^n))

I got some strange behavior (windows given rectangles larger than my 
screen) when q <= 0, I'm not sure whether it is reasonable to clamp the q 
value at 0.05 or something.

I think the algorithm for the list of heights might be clearer as follows 
(untested):

> heights h n q = correct $ map (round . (*fromIntegral h)) $ normalize
>                    $ take n $ iterate (/q) 1
>  where normalize x = let s = sum x in map (/ s) x
>        correct (x:xs) = (h - sum xs) : xs
>        correct _      = []

Thanks,
Adam