Add BinaryColumn layout

This is similar to 'Column' layout with some differences.

- Add/remove windows keeps window bounds.
- Enforce minimum window size.
- Negative scale can be used to increase the size of the last window
  instead of the master window.

CHANGES.md

@@ -94,6 +94,15 @@
     A new layout based on Dishes, however it accepts additional configuration
     to allow multiple windows within a single stack.
 
+  * `XMonad.Hooks.BinaryColumn`
+
+    A new module which provides a simple grid layout, halving the window
+    sizes of each window after master.
+
+    This is similar to Column, but splits the window in a way
+    that maintains window sizes upon adding & removing windows as well as the
+    option to specify a minimum window size.
+
 ### Bug Fixes and Minor Changes
 
   * `XMonad.Actions.Navigation2D`

XMonad/Layout/BinaryColumn.hs

@@ -0,0 +1,132 @@
+{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, TypeSynonymInstances #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  XMonad.Layout.BinaryColumn
+-- Copyright   :  (c) 2009 Ilya Portnov, (c) 2018 Campbell Barton
+-- License     :  BSD3-style (see LICENSE)
+--
+-- Maintainer  :  Campbell Barton <ideasman42@gmail.com>
+-- Stability   :  unstable
+-- Portability :  unportable
+--
+-- Provides Column layout that places all windows in one column.
+-- Each window is half the height of the previous.
+--
+-- Note: Originally based on XMonad.Layout.Column with edits.
+--
+-----------------------------------------------------------------------------
+
+module XMonad.Layout.BinaryColumn (
+                             -- * Usage
+                             -- $usage
+                             BinaryColumn (..)
+                            ) where
+import XMonad
+import qualified XMonad.StackSet
+import qualified Data.List
+
+-- $usage
+-- This module defines layot named BinaryColumn.
+-- It places all windows in one column.
+-- Windows heights are calculated that.
+--
+-- You can use this module by adding folowing in your @xmonad.hs@:
+--
+-- > import XMonad.Layout.BinaryColumn
+--
+-- Then add layouts to your layoutHook:
+--
+-- > myLayoutHook = BinaryColumn 1.0 32 ||| ...
+--
+-- The first value causes the master window to take exactly half of the screen,
+-- the second ensures that windows are no less than 32 pixels tall.
+--
+-- Shring/Expand can be used to adjust the first value by increments of 0.1.
+--
+-- 2.0 uses all space for the master window
+-- (minus the space for windows which get their fixed height)
+-- 0.0 gives an evenly spaced grid.
+-- Negative values reverse the sixes so the last
+-- window in the stack becomes larger.
+--
+
+data BinaryColumn a = BinaryColumn Float Int
+  deriving (Read, Show)
+
+instance XMonad.LayoutClass BinaryColumn a where
+  pureLayout = columnLayout
+  pureMessage = columnMessage
+
+columnMessage :: BinaryColumn a -> SomeMessage -> Maybe (BinaryColumn a)
+columnMessage (BinaryColumn q min_size) m = fmap resize (fromMessage m)
+  where
+    resize Shrink = BinaryColumn (max (-2.0) (q - 0.1)) min_size
+    resize Expand = BinaryColumn (min   2.0  (q + 0.1)) min_size
+
+columnLayout :: BinaryColumn a
+  -> XMonad.Rectangle
+  -> XMonad.StackSet.Stack a
+  -> [(a, XMonad.Rectangle)]
+columnLayout (BinaryColumn scale min_size) rect stack = zip ws rects
+  where
+    ws = XMonad.StackSet.integrate stack
+    n = length ws
+    scale_abs = abs scale
+    heights_noflip =
+      let
+        -- Regular case: check for min size.
+        f n size div False = let
+          n_fl = (fromIntegral n)
+          n_prev_fl = (fromIntegral (n + 1))
+          div_test = min (div) (n_prev_fl)
+          value_test = (toInteger (round ((fromIntegral size) / div_test)))
+          value_max = size - (toInteger (min_size * n))
+          (value, divide_next, no_room) =
+            if value_test < value_max then
+              (value_test, div, False)
+            else
+              (value_max, n_fl, True)
+          size_next = size - value
+          n_next = n - 1
+          in value
+          : f n_next size_next divide_next no_room
+        -- Fallback case: when windows have reached min size
+        -- simply create an even grid with the remaining space.
+        f n size div True = let
+          n_fl = (fromIntegral n)
+          value_even = ((fromIntegral size) / div)
+          value = (toInteger (round value_even))
+
+          n_next = n - 1
+          size_next = size - value
+          divide_next = n_fl
+          in value
+          : f n_next size_next n_fl True
+        -- Last item: included twice.
+        f 0 size div no_room_prev =
+          [size];
+      in f
+         n_init size_init divide_init False
+      where
+        n_init = n - 1
+        size_init = (toInteger (rect_height rect))
+        divide_init =
+          if scale_abs == 0.0 then
+            (fromIntegral n)
+          else
+            (1.0 / (0.5 * scale_abs))
+
+    heights =
+      if (scale < 0.0) then
+        Data.List.reverse (take n heights_noflip)
+      else
+        heights_noflip
+
+    ys = [fromIntegral $ sum $ take k heights | k <- [0..n - 1]]
+    rects = map (mkRect rect) $ zip heights ys
+
+mkRect :: XMonad.Rectangle
+  -> (Integer,XMonad.Position)
+  -> XMonad.Rectangle
+mkRect (XMonad.Rectangle xs ys ws _) (h, y) =
+  XMonad.Rectangle xs (ys + fromIntegral y) ws (fromInteger h)