Swap 2 Windows Associated by “Follow Mode”

Question

Say a frame is split (by C-x 3) into 2 windows that both display the same buffer.

If I enable follow-mode, the left window will always display the content closer to the beginning-of-buffer than the right one.

Q:

How to swap these two windows (so that the left window will display the content following what is displayed by the right one)

---

How my Emacs currently behaves:

emacs-version: 28.2
system-configuration: x86_64-w64-mingw32

Answer 1

To achieve the desired effect you need to change two lines in the source code of 'follow.el' as done below:

(defun follow--window-sorter (w1 w2)
  "Sorting function for W1 and W2 based on their positions.
Return non-nil if W1 is above W2; if their top-lines
are at the same position, return non-nil if W1 is to the
left of W2."
  (let* ((edge-1 (window-pixel-edges w1))
     (edge-2 (window-pixel-edges w2))
     (y1 (nth 1 edge-1))
     (y2 (nth 1 edge-2)))
    (if (= y1 y2)
;;  (< (car edge-1) (car edge-2)) ;; <<<===
    (< (car edge-2) (car edge-1))
;;      (< y1 y2))))  ;; <<<===
      (< y2 y1))))

See how it looks like if changed as above:

Knowing this above feel free to update my answer with code of a function follow-toggle-right-to-left-order toggling a value of follow-right-to-left-order variable used to switch the sorting order in follow--window-sorter.

Below the not yet tested code of a patch with the above mentioned functionality:

(setq follow-right-to-left-order nil)

(defun follow-toggle-right-to-left-order ()
  "toggle value used by  (defun follow--window-sorter ..."
  (= follow-right-to-left-order t
       (setq follow-right-to-left-order nil)
       (setq follow-right-to-left-order t)
  )
)

(defun follow--window-sorter (w1 w2)
  "Sorting function for W1 and W2 based on their positions.
  Return non-nil if W1 is above W2; if their top-lines
  are at the same position, return non-nil if W1 is to the
  left of W2."
  (let* ((edge-1 (window-pixel-edges w1))
         (edge-2 (window-pixel-edges w2))
         (y1 (nth 1 edge-1))
         (y2 (nth 1 edge-2))))
  (if (= y1 y2)
    (if follow-right-to-left-order
      (< (car edge-2) (car edge-1))
      (< (car edge-1) (car edge-2))
    ))
  (if  follow-right-to-left-order
      (< y2 y1)
      (< y1 y2)
  )
)
;;     *
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