A Standard for Thumbnailers

Benedikt Meurer benny at xfce.org
Thu Jan 11 02:25:34 PST 2007

Stanislav Brabec wrote:
>>> Haw widely used desktop-neutral thumbnailing library understanding many
>>> embedded thumbnails and providing thumbnailing for images without
>>> embedded thumbnail.
>> I think external thumbnailer as used by Thunar/Nautilus are better,
>> because it's more flexible and avoids loading various libraries required
>> to generate thumbnails for different formats into the processes.
> External binary thumbnailer has to initialize and load needed libraries
> again and again for each image. If you will have library, you can manage
> this better by using shared modules. For example you can load them on
> demand and unload after finishing of thumbnailing of the directory.
> For typical small and simple thumbnailer it saves only few milliseconds
> per image, for thumbnailers preloading larger libraries it may be more.

There are very good reasons to avoid this. You don't want to load
arbitrary code into the file manager (or any other process) just to
create a thumbnail. See Alex' for good reasons to avoid this.

>From the performance POV, we're talking about milliseconds, because it
doesn't really matter whether ld loads the shared libraries into our
process or into a new process. It's basicly the fork overhead, plus some
additional setting up (but since thumbnailers, except for the very basic
ones, will usually not benefit from previously performed file manager
initialization, except probably g_type_init() to use GdkPixbuf, this
doesn't take much time).

>> Using .desktop files to register thumbnailers instead of GConf should be
>> fine for desktop-neutral usage.
> I agree. Additionally GConf has no way to solve more-thumbnailes-per-
> MIME-type problem (later wins), desktop files can solve it (by mechanism
> of choosing defaults).

So, we're back on-topic. ;-)

>>> Thumbnails can use file system extended attributes.
>> Not every file system supports that. What would be stored in the
>> extended attributes anyway?
> If file system has extended attributes, maybe you can use them to store
> thumbnail. I am not sure about xattr limitations, but Apple's HFS uses
> something similar called resources to store thumbnails.
> If file system does not support it, the fall back to other methods.

This will work on certain platforms, but not on Linux, so you won't
benefit from it. Because the size of the xattr block is limited to a few
hundred bytes (while I'm not sure if it also applies to other file
systems or only ext3).

It doesn't sound like a sane solution anyway.


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