bug#59902: 30.0.50; Image overlay is not updated until the cursor moves to the overlay

[Ihor Radchenko]

Eli Zaretskii <eliz@gnu.org> writes:

>> No. Not really. Source block execution does not pass any information
>> about updating/not updating images to Org image display code. Even if it
>> did, the same issue could appear when the image file changes on disk
>> outside Emacs.
>
> Then I don't think I understand what you expect Emacs to do in these
> cases.  We have no idea when the image file is replaced, and cannot
> have such an idea without examining the file at high enough frequency.
> Doing this "from time to time" is going to miss some changes, or take
> note of them too late.  What else is possible?

For example, `create-image' could accept optional argument to update the
cached image if the file modification time is newer than it was when the
image was cached.

>> Yet, do note that flickering two different image versions when moving
>> point is unexpected even considering the information you provided.
>
> Flickering is expected when you do something that affects a large
> portion of the Emacs display.  For example, the same will happen if
> you change a large overlay at high enough frequency.  There's no way
> around that except not doing that.

Sorry, I used inaccurate word here.
What I am referring to here is image overlay displayed old and new image
when you move the cursor to the overlay and back repeatedly.

> Why was this implementation chosen for whatever feature that produces
> images?  Emacs doesn't react instantly to changes in disk files that
> it visits, and here you expect it to do so.  Isn't it possible to
> implement this in some other way, like have the program produce its
> image data in a temporary Emacs buffer, then use that buffer's
> contents for creating an image?  Then I believe the updated image will
> have a different hash value, and there will be no cache-related
> collisions.

It could be possible, but looks like unnecessary complication.
Also, creating buffers often creates overheads associated with user
hooks.

I am not sure if something like

(let ((revert-without-query '(".")))
                      (with-current-buffer (find-file-noselect file)
                        ;; Do not crown the buffer list.
                        (unless (string-prefix-p " " (buffer-name))
                          (setf (buffer-name) (concat " " (buffer-name))))
                        (buffer-string)))

is not going to cause significant slowdowns.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
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