ThreeColumnsMiddle

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+{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  XMonad.Layout.ThreeColumnsMiddle
+-- Copyright   :  (c) Carsten Otto <xmonad@c-otto.de>,
+--                based on ThreeColumns (c) Kai Grossjohann <kai@emptydomain.de>
+-- License     :  BSD3-style (see LICENSE)
+-- 
+-- Maintainer  :  ?
+-- Stability   :  unstable
+-- Portability :  unportable
+--
+-- A layout similar to tall but with three columns, where the main window is
+-- in the middle. With 2560x1600 pixels this layout can be used for a huge
+-- main window and up to six reasonable sized slave windows.
+--
+-- > Screenshot: http://server.c-otto.de/xmonad/ThreeColumnsMiddle.png
+--
+-----------------------------------------------------------------------------
+
+module XMonad.Layout.ThreeColumnsMiddle (
+                              -- * Usage
+                              -- $usage
+                              ThreeColMid(..)
+                             ) where
+
+import XMonad
+import qualified XMonad.StackSet as W
+
+import Data.Ratio
+
+import Control.Monad
+
+-- $usage
+-- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@:
+--
+-- > import XMonad.Layout.ThreeColumnsMiddle
+--
+-- Then edit your @layoutHook@ by adding the ThreeColMid layout:
+--
+-- > myLayouts = ThreeColMid 1 (3/100) (1/2) ||| etc..
+-- > main = xmonad defaultConfig { layoutHook = myLayouts }
+--
+-- The first argument specifies how many windows appear in the main window.
+-- The second argument specifies how much the main window size changes when resizing.
+-- The third argument specifies the initial size of the main window as a fraction of
+-- total screen size.
+--
+-- For more detailed instructions on editing the layoutHook see:
+--
+-- "XMonad.Doc.Extending#Editing_the_layout_hook"
+
+data ThreeColMid a = ThreeColMid !Int !Rational !Rational deriving (Show,Read)
+
+instance LayoutClass ThreeColMid a where
+    doLayout (ThreeColMid nmaster _ frac) r =
+        return . (\x->(x,Nothing)) .
+        ap zip (tile3 frac r nmaster . length) . W.integrate
+    handleMessage (ThreeColMid nmaster delta frac) m =
+        return $ msum [fmap resize     (fromMessage m)
+                      ,fmap incmastern (fromMessage m)]
+            where resize Shrink = ThreeColMid nmaster delta (max 0 $ frac-delta)
+                  resize Expand = ThreeColMid nmaster delta (min 1 $ frac+delta)
+                  incmastern (IncMasterN d) = ThreeColMid (max 0 (nmaster+d)) delta frac
+    description _ = "ThreeColMid"
+
+-- | tile3.  Compute window positions using 3 panes
+tile3 :: Rational -> Rectangle -> Int -> Int -> [Rectangle]
+tile3 f r nmaster n 
+-- split horizontally, if there are very few windows (only the main screen is used)
+    | n <= nmaster || nmaster == 0 = splitHorizontally n r
+
+-- one window more than the master window can hold (the additional window is shown right of the main screen)
+    | n == nmaster+1 = splitVertically nmaster s1 ++ splitVertically (n-nmaster) s2
+
+-- many windows (the main windows are shown in the center, all other windows are shown left and right of it)
+    | otherwise = splitVertically nmaster r1 ++ splitVertically nleft r2 ++ splitVertically nright r3
+  where (r1, r2, r3) = split3HorizontallyBy f r
+        (s1, s2) = splitHorizontallyBy f r
+        nslave = (n - nmaster)
+        nleft = ceiling (nslave % 2)
+        nright = (n - nmaster - nleft)
+
+split3HorizontallyBy :: Rational -> Rectangle -> (Rectangle, Rectangle, Rectangle)
+split3HorizontallyBy f (Rectangle sx sy sw sh) =
+    ( Rectangle (sx + fromIntegral leftw) sy midw sh
+    , Rectangle sx sy leftw sh
+    , Rectangle (sx + fromIntegral leftw + fromIntegral midw) sy rightw sh )
+  where midw = ceiling $ fromIntegral sw * f
+        leftw = ceiling ( (sw - midw) % 2 )
+        rightw = sw - leftw - midw