[Marble-devel] New scanline access method
carlos_licea at hotmail.com
Sat Nov 7 19:33:06 CET 2009
On Sábado 07 Noviembre 2009 02:59:55 Torsten Rahn escribió:
> Hi Carlos,
> Interesting indeed (I wasn't aware of the detach).
> Have you tried without changing the c-cast into a reinterprete cast?
The C-style cast rules go as follows:
The semantics for a cast-expression (aka a 'C-Style Cast') are defined as the
first of these that succeeds: const_cast, static_cast, static_cast followed
by const_cast, reinterpret_cast, reinterpret_cast followed by const_cast. See
In this context the static_cast is not possible (there's no "legal" way to
transform a bunch of uchar to a QRgb), so, what is happening is a
reinterprete_cast. That's why the old c-style is not recommended anymore. You
don't really know which combinations of casting are happening behind the
> Am Samstag 07 November 2009 08:08:58 schrieb Carlos Licea:
> > List,
> > Reading through the planet I found this post:
> > http://zecke.blogspot.com/2009/11/collecting-hints-to-increase.html
> > When I checked the repository I found:
> > http://gitorious.org/qt-performance/qt-performance/blobs/master/performa
> >nc e- guide/qimage.xml
> > I immediately remembered that we use QImage::scanLine method in the
> > ScanLine approach and sat down to try the new approach.
> > Here you have the patch.
> > Short story: doesn't seem to work.
> > Long story: I didn't do any very deep analysis just ran marble with the
> > option --timedemo and here are the results (they are not averages of
> > multiple runs, I just ran them a couple of times and wrote the value
> > once when I saw that I didn't have any gains):
> > Old approach New approach
> > Spherical 45414ms"=4.40383 fps" 58491ms"=3.41933 fps"
> > Equirectangular 58673ms"=3.40872 fps" 61583ms"=3.24765 fps"
> > Mercator 66459ms"=3.00937 fps" 71495ms"=2.7974 fps"
> > It's really thrilling that we not only we are not improving, but that we
> > are having even worse performance.
> > Carlos
> > PS: I couldn't CC the author of the post. I wasn't able to find his email
> > address (not that I really, really tried).
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