Why is Qtopia much faster?

Carsten Haitzler (The Rasterman) raster at openmoko.org
Tue Jul 22 15:33:21 CEST 2008

On Tue, 22 Jul 2008 19:10:27 +1000 Lorn Potter <lpotter at trolltech.com> babbled:

> Tilman Baumann wrote:
> > And not using x11 is probably a very sane step, if you can live  
> > without the portability factor. (That's porting other apps)
> There is no portability factor. Only which toolkit is available.
> As one of our engineers here said on our internal discussion (and goes 
> back to rasters comment):
> "One of the neat advantages of Qtopia on Qt for Embedded Linux is that 
> there is little penalty in converting back and forth between a QImage 
> and QPixmap so we have used this extensively which makes quite a few 
> things much easier and more possible than if things are based on X11 
> where these conversions are expensive and you then need to put a bit 
> more thought in to it. "

yup. for qws your conversions are cheap/almost free, but in x11 - not so. it
probably is a matter of working with the x11 port of qtopia or changing the
assumption that such conversions are cheap/free (eg never even using pixmaps -
do everything software-rendered in client-space virtual framebuffers, as this
is exactly what happens with qtopia on qws with a dumb fb anyway). this
will never allow seamless acceleration and gfx-chip side functions doing as
much work as they can, but will probably function about as well as qtopia with
qws natively on a freerunner.

so indeed - you are right. you made an ASSUMPTION of qws and these things being
cheap conversions - though that may not be the case for some accelerated back
ends for qws... but anyway - it can be improved.many options as to how to do
it. x11 itself is not really a performance bottlneck - it is just the way you
use it that makes the difference between it being "a blocker for performance"
and a "it doesnt matter". :)

Carsten Haitzler (The Rasterman) <raster at openmoko.org>

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