bug#68006: 30.0.50; Image-mode speed

[Manuel Giraud]

Eli Zaretskii <eliz@gnu.org> writes:

[...]

> Using img->timestamp is not reliable enough, since that timestamp is
> updated each time we call prepare_image_for_display, which can happen
> many times during a session for the same image, and not necessarily
> for actually displaying the image in a window.  For example, AFAICT if
> you move across an image with C-n/C-p, we update the time stamp each
> time vertical motion crosses the screen line with the image.  So I
> think we'd need to store the file's time stamp or some other
> signature.

Right.

> The comparison with times-less-p is also risky: what if someone
> replaces the image file with an older file?

I don't understand what the risk is here?  It is just a cache.

> I'd trust some kind of file checksum better, which we will have to
> store alongside the image spec or as part of it.  (Don't we already do
> something like that somewhere in image-*.el files?)

For image-dired, there is 'image-dired-contents-sha1'.  Maybe this the
one you thought about?
-- 
Manuel Giraud