Abdelrazak Younes wrote: > Abdelrazak Younes a écrit : >> Andre Poenitz a écrit : >>> On Thu, Mar 16, 2006 at 10:50:41AM +0100, Abdelrazak Younes wrote: >>> >>>>> I thought even painting into a pixmap should only be done in a >>>>> paintEvent(). The pixmap is located on the server side after all... >>>>> >>>> I don't think so... or maybe I don't understand what you mean by >>>> "server side". >>>> >>> >>> The X server. >>> >>> A 'pixmap' is located on the X server, whereas an 'image' is located on >>> the X client. So pixel manipulation is cheap on images, display is >>> (reaonably) cheap for pixmaps. And I though (but am not sure) that >>> one accesses the server only in paintEvents nowadays. >>> >> I think there is some "qui-proquo" here. What I call the backing pixmap >> in QWorkArea is a QPixmap which is an off-screen, pixel-based paint >> device. So it is really an image even if it rely in windowing system, in >> this case the X server. The painting of this image into screen handled >> by the Xserver is indeed done in QWorkArea::paintEvent() and that is the >> one and only painting of the buffer view onto the screen. This was just >> for clarification and I think we agree on everything except the fact >> that QPixmap can be painted into at any time. > > Hum, after thinking a bit more about this, I am maybe wrong here when > the windowing system is an X11 server. Georg's post pushed me to try > using a backing QImage instead of a QPixmap. I cannot feel any speed > difference within Windows but I guess it can make a big difference on > X11. Especially over the network as pointed by Georg. Besides, the code > is cleaner and a bit shorter.
I cannot test now over a really slow connection, but on a 100 MBit network I see a performance loss with the patch for pressing PgDown multiple times in a document with some graphics and formulas, but I guess a real test would be to do this on a slower network. I don't see any difference if not running over the network. The rason for the performance loss might be that with your patch the image data goes over the network whenever QWorkArea::paintEvent is called. It is probably cheaper to do simple image manipulations over the network, but let the pixmap data reside in the X server instead of transferring it for every paint event. BTW I guess you read http://doc.trolltech.com/4.1/qpixmap.html ? Georg
