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Re: Can I avoid using `clear-image-cache'?


From: Mathias Dahl
Subject: Re: Can I avoid using `clear-image-cache'?
Date: Mon, 09 May 2005 08:01:41 +0200
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/21.3.50 (windows-nt)

Thien-Thi Nguyen <address@hidden> writes:

> i just looked at image.c:1661 (lookup_image), which sez:
>
>   /* If not found, create a new image and cache it.  */
>   if (img == NULL)
>
> probably immediately prior to this block is the best place to add
> a file timestamp check.  that's not as pretty a solution as fully
> generalizing the check to some kind of `:volatile VOLATILE-SPEC':
>
>   :volatile VOLATILE-SPEC
>
>   If VOLATILE-SPEC is t, take extra steps to check for "image
>   change" so that image-cache lookup can DTRT [obviously this
>   documentation can be improved ;-].  If :file is specified,
>   use the timestamp of the file.  Otherwise, compute a hash of
>   the data and use that to detect change.
>
>   VOLATILE-SPEC may also be a function that takes one argument,
>   either the file timestamp or the data (as a string), and returns
>   non-nil to indicate that the image has changed.
>
> i was all fired up and ready to do some quick munging and post
> code (thereby procrastinating on other emacs munging for vms :-),
> but then i saw how image.c leaves file loading to each image type
> (not enough abstraction for my tastes) so all the gumption seeped
> away...
>
> perhaps post-release i (or someone else) will do the requisite
> refactoring so that :volatile or like can be added more easily.

Sounds like a good idea. I can wait, my hack is working quite nicely
for now.

/Mathias


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