Mipmapping for canvas. Ideas and comments.

Boudewijn Rempt boud at valdyas.org
Wed Jul 22 09:48:21 CEST 2009

On Wed, 22 Jul 2009, Cyrille Berger wrote:

> 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).

Just to make sure: I didn't write what you quoted :-). Another difference is that QPixmap, afaik,
doesn't have transparency, which QImage has.

> > 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.

That would be very nice :-)


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