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List:       kde-devel
Subject:    Re: Folder previes in Dolphin
From:       Peter Penz <peter.penz () gmx ! at>
Date:       2008-11-17 7:46:15
Message-ID: 200811170846.16101.peter.penz () gmx ! at
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On Monday, 17. November 2008 00:04:46 Jesse L. Zamora wrote:
> On Sunday 16 November 2008 13:30:19 Peter Penz wrote:
> > Yes, having different icon sets is a problem by its own. But I think the
> > real difficult part is the synchronization of the preview cache and the
> > content of the folder: We cannot create the preview on-the-fly when
> > entering a directory, as this would mean that we'd have to parse each sub
> > directory and create 4 previews for each sub directory, which would lead
> > to an unacceptable performance. Providing a cache and storing the preview
> > e. g. inside the .directory file  would introduce the problem when the
> > cache should by synchronized with a possible changed directory content.
>
> Well, actually, I wonder if it wouldn't be too bad to create a
> multithreaded implementation that loads the previews into the cache without
> disturbing whatever the user is doing, and then just showing it once it has
> loaded.

Previews are generated asynchronously anyhow already and although the UI won't 
be blocked, still your system performance goes down. You can see the effect 
already when turning on the Information Panel: The image preview is created 
asynchronously and the meta data are also received asynchronously (KDE 4.2), 
but still it has side effects to the felt performance when entering a 
directory having several hundreds of items (they are also loaded 
asynchronously).

Now assuming a directory is opened with 20 folders you'd have to create 80 
previews on-the-fly, which might decrease the system performance for more than 
20 seconds (assumption: creating a preview of a non-cached JPEG image takes 
250 ms).

This does not mean that I would not want to have this feature (it's the 
opposite: it would be great having this feature), but implementing it in a way 
that the balance between system load and showing outdated/wrong pictures is 
given is not trivial. But let's see what we can do for KDE 4.3...

Best regards,
Peter


 
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