preview in dolphin is slow with many pictures

[Peter Penz]

Hi Mathias,

I think I've some good news for you :-)

On Thursday, 12. June 2008 23:46:03 Mathias Kraus wrote:
[...]
> some suggestions for preview:
> -start from top left, instead from bottom right, if easy doable
> -start with images that are completely in the visible area, not only
> partly, but I think this will be more expensive
[...]

I've spend quite a lot of time during the last days to do some profiling and 
find the bottlenecks for the preview generation. The following improvements 
are now in SVN:

- the previews are always generated for the visible area first from the 
top-left to the bottom-right (no matter which kind of sorting is used)

- if the previews for the invisible items are generated, the UI is not blocked 
anymore and the generation is done now very fast (even in the debugging mode)

In my tests when having a folder with 1000 images and scrolling through the 
view during preview generation resulted in no blocking of the UI. Dolphin in 
KDE 4.0.x took 19 seconds for generating previews of 772 images (release 
mode) and Dolphin for KDE 4.1 only takes around 4 seconds (debug mode) for 
the same task although nicer (and more expensive) image frames are drawn and 
the visible area is considered too.

I did also some tests with a folder having 10000 items and here some blocking 
is done when opening the folder or after moving the visible area, but the 
root here is a combination how QListView receives the maximum size of an item 
and how Dolphin calculates this size and not the preview generation itself.

However I think this is a good base for KDE 4.1 and hope you'll like it :-)

Best regards,
Peter