[Kde-graphics-devel] Descriptions of new stuff

[Lubos Lunak]

On Wednesday 15 of December 2004 15:30, Mosfet wrote:
>
> ***Smoothscaling:
> Since this is done a lot it is what everyone tries to optimize. Qt uses a
> method based on NetPBM and is mostly integer. It's pretty good. The first

 Qt's QImage::smoothScale() is pretty good only if you find it acceptable that 
something called "smoothscale" doesn't actually bother to smooth while 
scaling. Enlarge some image in basically any Qt/KDE image viewer (Gwenview 
being probably the only exception) and enjoy the Lego building blocks.

> thing I did was add some MMX and 3dnow inline asm. I was able to use
> doubleword operations to handle two pixel components at once and reciprocal
> 3dnow multiplication for the division. It was about twice as fast as the
> original NetPBM/Qt version.
>
> Then I got a look at Imlib2's scale. It replaces most of the integer
> multiplication and division with fast bit shifts. Fairly complicated code,
> but the normal C version runs as fast as my MMX optimized one, (twice as
> fast as Qt/NetPBM). The MMX optimized Imlib2 scale runs twice as fast as my
> MMX optimized one and 4x as fast as Qt. Definitely a good one here.
>
> I've finished porting both the C and asm Imlib2 scales to QImage. It was a
> pretty straightforward port of Imlib's scale.c. Mostly I just stuck
> everything in a namespace, moved things around to work off of Qt BGRA
> scanlines, and removed the unneeded border code, (as well as fixed the
> formatting ;-). Seems to run fine. The asm routines did not need to be
> modified at all.

 I might have missed this in one of the previous mails, but is there some URL 
pointing to the sources? I'd be interested in this, because I've ported 
ImageMagick's scaling code for Gwenview 
(http://webcvs.kde.org/kdeextragear-1/gwenview/gvimageutils/scale.cpp) after 
realizing the shortcomings of Qt's smoothScale() (well, and scale() actually 
as well - interesting how one doesn't mind until the problems show in an 
image viewer). It produces very good results, and is about as fast as the Qt 
functions, but I wouldn't mind dumping it for something that's just as good 
and faster :).

-- 
Lubos Lunak
KDE developer
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