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List:       kde-devel
Subject:    Re: Animation with QPainter
From:       Uwe Thiem <uwix () iway ! na>
Date:       2006-11-30 18:33:40
Message-ID: 200611302033.42707.uwix () iway ! na
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On 30 November 2006 19:31, Matt Newell wrote:
> On Thursday 30 November 2006 08:45, Matej Svejda wrote:
> > Hi!
> >
> > I want to include an animation in my program (a metronome for KDE 3.5). I
> > used QPainter for painting and QTimer for the animation.
> > What bothers me is that the animation just isn't smooth. First I directly
> > painted via e.g. QPainter::drawRect. Then I read somewhere that it is
> > better to create a Pixmap and then use it. I did get a little better
> > results with that but there still is this really anoying flickering.
> > Maybe someone could tell me what I'm doing wrong or whether there is a
> > better way to do this.
> > The code for the animation can be downloaded here:
> > http://www.aw-modell.at/mata/animationtest.tar.gz
> >
> > Thanks for any kind of help!
> > Matej
>
> Pass this to the widgets wflags
> Qt::WNoAutoErase - indicates that the widget paints all its pixels.
> Updating, resizing, scrolling and focus changes should therefore not erase
> the widget. This allows smart-repainting to avoid flicker.

Hm... with a Qtimer triggered draw function that draws the new pixmap and 
bitBlt() it to the QWidget, there shouldn't be any flickering anyway.

Alright, had a look at the demo code. Don't call update() in move(). Instead, 
draw your pixmap in move() and bitBlt() it. 

On the other hand, there seems to be a better way to do it. You are wasting a 
lot of CPU cycles for redrawing the pixmap over and over. If your metronome 
isn't too big so that memory isn't an issue, you could pre-draw a couple of 
pixmaps and simply bitBlt() the next one in move().

Uwe

-- 
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http://www.SysEx.com.na
 
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