Re: How to temporarily show an image in an Emacs buffer?

[Ruijie Yu via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>]

Marcin Borkowski <mbork@mbork.pl> writes:

> On 2023-03-08, at 05:53, Marcin Borkowski <mbork@mbork.pl> wrote:
>
>> Alternatively, it _may_ change the buffer contents but in a way that is
>> not recorded in `buffer-undo-list'.  Is that possible?
>
> I did some experimenting, and this
>
> (defvar no-undo-marker (make-marker))
> (defun no-undo-insert ()
>   "Test undo."
>   (save-excursion
>     (let ((buffer-undo-list))
>       (set-marker no-undo-marker (point))
>       (insert "this can't be undone\n"))))
>
> (defun no-undo-uninsert ()
>   (save-excursion
>     (goto-char no-undo-marker)
>     (let ((buffer-undo-list))
>       (when (looking-at-p "this can't be undone\n")
>   (delete-char 21)))))
>
> seems to do the trick, but depending on the order of typing and calling
> these functions, the undo list becomes corrupted (I get "primitive-undo:
> Changes to be undone are outside visible portion of buffer").
>
> Any hints?

Maybe you can make use of overlays [1]?  That sounds like a great fit
according to the description of your need.

[1]: (info "(elisp) Managing Overlays")

--
Best,


RY