[Digikam-devel] [Bug 137320] Thumbnails should continue loading for images that are off-screen

[Mikolaj Machowski]

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http://bugs.kde.org/show_bug.cgi?id=137320         




------- Additional Comments From mikmach wp pl  2008-03-18 08:54 -------
> b) maybe pre-load the next line (or next two lines) into the pixmap cache.


This is moment for user input ;)

One line is definitely too small.

1) Lest advanced users are scrolling only by one line but it allows them 
to scan those images quickly and if they are not satisfied they go to 
next line. Will be caching mechanism quick enough to load rows fast?

2) More advanced users use scrolling whell with more flourish which 
usually is equal to ca. half of screen of new images. Number of new rows 
depends on size of thumbnails, but it should be 2-3 rows.

3) Most advanced users jump by PageUp/PageDown or scroll wheel equivalent.

So, preloading of one row will satisfy only one group of users and not 
in all scenarios. Globally, they make the most numerous group of 
software users but due to geekiness factor they are probably weakly 
represented among Linux/KDE/digiKam users.

The best preloading, which will satisfy all users is preloading of whole 
neighbouring screen of thumbnails.

Don't know if this is possible but: in ImageMagick is switch -size. 
According to docs it tells libjpeg [sic!] to load only limited number of 
bytes to satisfy users request. It is used to speed up execution and to 
lessen memory usage. Wording suggests it is libjpeg feature so it can be 
used by other programs as well. Main problem is this applies to libjpeg 
and thumbnails in .thumbnails are PNGs... Quick scan of libpng 
documentation shows possibility to read images in chunks (interlacing). 
Maybe this could speed some things? Just random thought of 
non-programmer.

I am suggesting this because in many cases when browsing Album I don't 
have to see 100% perfect thumbnail. I see green blobs, not for me, I am 
looking for blue blobs (sea), go next screen.

Several versions ago digiKam has similar mechanism with auxiliary 
database of bastardized images. Due to improved preloading mechanisms 
this was scrapped but maybe this is time to investigate similar solution?

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