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From: Aidan Hall <aidan.hall202@gmail.com>
Newsgroups: comp.emacs
Subject: Re: Sharing my split-window-preferred-function that splits at (pixel-wise) longer window-edge
Date: Wed, 17 Dec 2025 19:16:10 +0000
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Mekeor Melire <mekeor@posteo.de> writes:

> (defun split-window-rationally (&optional window)
>   "Split window at its pixelwise longer edge."
>   (interactive)
>   (let ((window (or window (selected-window)))
>         (split-height-threshold 0)
>         (split-width-threshold 0)
>         (ratio (>= (window-pixel-width) (window-pixel-height))))
>     (with-selected-window window
>         (cond ((and ratio (window-splittable-p window t))
>                (split-window-right))
>               ((and (not ratio) (window-splittable-p window))
>                (split-window-below))
>               ((window-splittable-p window t)
>                (split-window-right))
>               ((window-splittable-p window)
>                (split-window-below))))))

I like the general idea of splitting based on pixel widths, since it
makes the logic independent of a given window's text scale. One issue
with this function is that it doesn't account for characters generally
being taller than they are wide.

You could do something similar using "scale independent window
width/height in characters", computed like so:

(/ (window-pixel-width) (frame-char-width))

Both your approach and this degrade (somewhat) gracefully to character
counts in terminal frames, where:
(window-pixel-width) = (window-width)
(frame-char-width) = 1