emacs: simple window splitting policy

init.el

;; Try to ensure sensible window splitting, independent of frame and font size.
;; Things I don't want: 
;; - excessive horizontal splitting (generally I prefer no more than 2 windows across)
;; - horizontal splitting when frame is tall and narrow (causing eg useless narrow man page formatting)
;; So, aim for a simple policy: popup windows shall be half width in a wide frame, 
;; half height in a tall frame.
;;
;; Emacs' window splitting behaviour is complex and must be read carefully.
;; In particular, note: it checks split-window-height first, and if that permits it to
;; split vertically, it does that and split-window-horizontally is ignored.
;;
;; Approach 1: set split-window-height to the full screen (frame-height) and
;; split-window-width to half the full screen (frame-width).  Problem: these
;; numbers change as the font is resized.
;;
;; Approach 2: update the split thresholds dynamically whenever window
;; configuration changes.  Inspect the current frame aspect ratio. If it is
;; wide, set split-window-height to frame height and split-window-width to
;; half frame width. If it is tall, set split-window-height to frame height
;; and split-window-width to full frame width.
;;
(defun adjust-window-split-thresholds nil 
  "Adjust split thresholds so that popup windows always split vertically in a tall frame, horizontally in a wide frame, with a maximum of two columns"
  (interactive)
  (if (>= (frame-pixel-width) (frame-pixel-height))
      ; wide frame
      (progn
        (setq split-height-threshold (frame-height))
        (setq split-width-threshold  (/ (frame-width) 2))
        )
      ; tall frame
      (progn
        (setq split-height-threshold (frame-height))
        (setq split-width-threshold  (frame-width))
        ))
  )
(add-hook 'window-configuration-change-hook 'adjust-window-split-thresholds)
;; (remove-hook 'window-configuration-change-hook 'adjust-window-split-thresholds)