bug#68006: 30.0.50; Image-mode speed

[Eli Zaretskii <eliz@gnu.org>]

> From: Manuel Giraud <manuel@ledu-giraud.fr>
> Cc: 68006@debbugs.gnu.org
> Date: Fri, 29 Dec 2023 12:11:44 +0100
> 
> What about this new patch?  It works for me as intended but might need
> better names and better docs.  Thanks.
> 
> +(defcustom image-mode-eager-cache-flush t
> +  "Non-nil means flush image from cache eagerly.
> +When set to nil, be aware that the image cache could grow fast
> +but an image previously displayed will show faster."

This doc string should explain the effects better, in terms of
user-facing behavior, not in terms of technical aspects of the code.

> -    ;; Discard any stale image data before looking it up again.
> -    (image-flush image)
> +    (if image-mode-eager-cache-flush
> +        ;; Discard any stale image data before looking it up again.
> +        (image-flush image)
> +      ;; Add a content based hash into image spec to be sure that the
> +      ;; cache is updated should the on disk image change.
> +      (when (and filename (file-exists-p filename))
> +        (setq image (append image (list :hash (image-contents-sha1 filename))))))
> +

I'm probably missing something: how would this assure that if the
image file is replaced, we re-read it from disk?

> +(defun image-contents-sha1 (filename)
> +  "Compute the SHA-1 of the first 4KiB of FILENAME's contents.  The
> +first 4KiB does not represent the whole file but was chosen
> +because it is fast enough for interactive usage."

The first line of a doc string should be a single complete sentence.

Thanks.