Mipmapping for canvas. Ideas and comments.

Cyrille Berger cberger at cberger.net
Wed Jul 22 09:42:42 CEST 2009

On Wednesday 22 July 2009, Boudewijn Rempt wrote:
> > Pixmaps reside on the xserver and are fast to paint over and over again
> > Images reside on the client and are good if you need to poke at the
> > pixels or change it every time you display it
This is not always true. This is currently true, on linux if you use the 
default engine "native", but if you use "raster" QPixmap are treated as a 
qimage, and they use the X Shared Memory extension to make cheap copy with a 
XPimap [1] (not sure about the GL engine, but I would suspect that are stored 
as textures).

> There is also the difference between xrender capable systems and
> non-xrender capable systems. If I remember correctly, we use QImage by
> preference, but if xrender isn't available, we use QPixmap.
Maybe for Qt4.6 when the raster engine is considered more stable, it will be 
worth to replace this by an option to switch to the "raster" engine and clean 
our code.

[1] http://labs.trolltech.com/blogs/2008/10/22/so-long-and-thanks-for-the-
Cyrille Berger
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