Rescreen: collects new screen information

Rescreen.hs

@@ -0,0 +1,41 @@
+-- Grabs new screen information.  Useful for randr setups.
+-- To use rescreen, add a keybinding in Config.hs. For example:
+-- , ((modMask .|. shiftMask, xK_F12   ), rescreen)
+
+-- TODO Get this code into xmonad when it is ready for randr support.
+-- Make it happen automatically on randr events.  It's currently 20 loc, but I
+-- believe it can be shrunk a bit.
+
+module XMonadContrib.Rescreen (rescreen) where
+
+import qualified StackSet as W
+import XMonad
+import Operations
+
+import Graphics.X11.Xlib
+import Graphics.X11.Xinerama
+
+import Control.Monad.State
+import Control.Monad.Reader
+import Data.List (partition)
+
+rescreen :: X ()
+rescreen = do
+    dpy    <- asks display
+    xinesc <- io $ getScreenInfo dpy
+    -- TODO: This stuff is necessary because Xlib apparently caches screen
+    -- width/height.  Find a better solution later.  I hate Xlib.
+    let sx = maximum $ map (\r -> rect_x r + fromIntegral (rect_width  r)) xinesc
+        sy = maximum $ map (\r -> rect_y r + fromIntegral (rect_height r)) xinesc
+    modify (\s -> s { xineScreens = xinesc, dimensions = (sx, sy) })
+    ws <- gets windowset
+    let s = W.current ws : W.visible ws
+        t = zipWith const [0 :: ScreenId ..] xinesc
+        (stay, hide) = partition (\x -> fromIntegral (W.screen x) < length t) s
+        newsids = filter (\x -> fromIntegral x >= length s) t
+        (newvis, newinvis) = splitAt (length newsids) (map W.workspace hide ++ W.hidden ws)
+        (newcurr : xs) = stay ++ zipWith W.Screen newvis newsids
+    windows $ const $ ws { W.current = newcurr
+                         , W.visible = xs
+                         , W.hidden  = newinvis
+                         }