How to set display margins for markdown-mode buffers?

Question

Is there a way to set the display margins for markdown-mode buffers? I've read https://www.gnu.org/software/emacs/manual/html_node/elisp/Display-Margins.html and various suggested solutions but nothing has worked for me. This is what I have currently:

(defun my-margins ()
  (set-window-margins (selected-window) 30 30))

(add-hook 'markdown-mode-hook 'my-margins)

However, nothing happens when I open a .md file. If I evaluate (my-margins) manually, however, then I get the desired result, until I switch to a different buffer, and then the margins are lost.

Ideally, I would like all markdown-mode buffers to have the desired display margins, regardless of whether I open a new frame, switch buffers, etc.

@TristanRiehs Yes, that's my intention. Is there a better way to do this? — jth, Jul 04 '23 at 20:46
Yes, the `visual-fill-column-center-text` feature from [visual-fill-column](https://github.com/joostkremers/visual-fill-column) allows you to do it very easily. @jth — Tristan Riehs, Jul 05 '23 at 10:29

score 0 · Answer 1 · answered Jul 03 '23 at 18:19

When you call the my-margins function you provided using markdown-mode-hook, selected-window does not return the window you expect. For example, if you call find-file test.md from the *scratch* buffer, selected-window will return the window displaying the *scratch* buffer, not the new one displaying the buffer of test.md.

To make your function work, you can call it from another hook, one where in the previous example selected-window would return the window displaying the markdown file. You can use window-configuration-change-hook.

We have to adapt my-margins since this hook is not only fired in markdown-mode :

(defun markdown-margins ()
  (when (equal major-mode 'markdown-mode)
    (set-window-margins (selected-window) 30 30)))

(add-hook 'window-configuration-change-hook 'my-margins)

How to set display margins for markdown-mode buffers?

1 Answers1