[Qt-interest] QGLWidget

[Fabien Brachere]

Le mardi 26 mai 2009 à 16:46 -0400, Nathan Carter a écrit :
> I have an application I've written and am compiling in Qt 4.5.  It  
> uses a QGLWidget subclass I've written.  I create one instance of the  
> subclass and keep it offscreen, so that when previews of things need  
> to be generated, that object can be configured/populated with the  
> stuff to render, and then I call QGLWidget::renderPixmap() on it,  
> returning a pixmap.
> 
> The problem is that on Mac and Windows this works great, but on Linux  
> the pixmaps returned are full of garbage data.  This is not a memory  
> issue (i.e., accessing freed memory) as far as I know, because my code  
> looks like this:
> 
> 	// quickviewer is the instance
> 	quickviewer->resize( w, h ); // desired width and height
> 	QPixmap p = quickviewer->renderPixmap();
> 	p.save( "test.png", "PNG" );
> 	// inspect that file and it contains garbage;
> 	// use p in the application and it shows up as garbage
> 
> You see, no moment when any deallocation occurs, as far as I can  
> tell.  And yet, when I say "garbage" I mean streaks of random colors  
> and little bits of other images in memory, indicating I'm accessing  
> memory I shouldn't be accessing.  Thus, my confusion.
> 
> Anyone else run across this same Linux-specific problem?  Did I do  
> something wrong?
> 

I had the same problem with my Linux box and not Windows. It was a
problem with the graphic's card driver (proprietary ATI driver). I
updated my distribution to Mandriva 2009.1 and it was solved.
I noticed that the problem doesn't occur with Qt 4.4.

Fabien