[Qt-interest] QPixmap, QMovie and memory consumption

[Nikos Chantziaras]

I'm using a QMovie to load an MNG animation, and then draw the 
individual QMovie::currentPixmap() frames using QPainter::drawPixmap().

However, when deleting the QMovie instance, the memory is not freed. 
For example, when the QMovie finishes playing, the application is at 
about 200MB RAM consumption.  About 180MB of those are attributed to QMovie.

When I use QMovie::currentImage() and draw it with QPainter::drawImage() 
instead, then there's no problem.  When deleting the QMovie, memory 
consumption jumps down to about 20MB again.

What is the problem?  The docs suggest that on X11 "a QPixmap is stored 
on the server side while a QImage is stored on the client side".  Does 
that mean that every QPixmap ever created by the application will linger 
around forever with no possibility to reclaim the used memory unless the 
application quits?

I'd use QImage instead of QPixmap, but according to the docs, "QImage is 
designed and optimized for I/O, and for direct pixel access and 
manipulation, while QPixmap is designed and optimized for showing images 
on screen."  Though it doesn't try to explain what "optimized" means 
exactly, so I have no idea what I would lose if I switch from pixamps to 
images.