Re: [RFC] making image-dired thumbnail creation asynchronous

[Eli Zaretskii]

> Date: Fri, 16 Dec 2016 08:15:31 -0500
> From: Mark Oteiza <address@hidden>
> Cc: address@hidden
> 
> @@ -868,10 +1004,9 @@ image-dired-display-thumbs
>            (goto-char (point-max)))
>          (dolist (curr-file files)
>            (setq thumb-name (image-dired-thumb-name curr-file))
> -          (if (and (not (file-exists-p thumb-name))
> -                   (not (= 0 (image-dired-create-thumb curr-file 
> thumb-name))))
> -              (message "Thumb could not be created for file %s" curr-file)
> -            (image-dired-insert-thumbnail thumb-name curr-file dired-buf))))
> +          (when (not (file-exists-p thumb-name))
> +            (image-dired-create-thumb curr-file thumb-name))
> +          (image-dired-insert-thumbnail thumb-name curr-file dired-buf)))
>        (if do-not-pop
>            (display-buffer buf)
>          (pop-to-buffer buf))
> 
> Here is the relevant hunk. image-dired-create-thumb is the starting
> point for asynchronous thumbnail creation. At this point,
> image-dired-insert-thumbnail is called immediately after invoking
> image-dired-create-thumb, so in practice the buffer has already been
> populated with images for files that potentially do not yet exist; i.e.
> the buffer contents are already finished changing before thumbnails are
> created.
> 
> There is currently nothing notifying Emacs once a thumbnail has been
> created, but it would go somewhere in image-dired-create-thumb or one of
> the functions its sentinel calls (the hunk previous to the one I pasted)

If the function that senses that the file was created re-inserts the
thumbnail image into its buffer, redisplay will happen automatically.

AFAIK, we don't have any infrastructure for delayed loading of images
that would do the above for you, but I guess something like that could
be implemented based on file notifications.