Image-based widgets showing is too slow in Qt 4.2.1

[mkrentovskiy]

Try increasing the pixmap cache, with QPixmapCache::setCacheLimit(int).
If I remember correctly you have to pass a number of kilobytes there. An 1280*1024 pixmap will automatically not be cached since the initial limit is 1Mb.

I increased cache limit up to 32Mb but flash in show/hide-operations still going on. But redrawing is a faster subjective.

Next, maybe you can make some use for QPaintEvent::rect and update only the dirty area.

Its right but not for total widget repainting when all visible area are dirty.

[marcel]

Its right but not for total widget repainting when all visible area are dirty.

Yes, but at least you can get faster updates for smaller dirty areas.

Regards

[mkrentovskiy]

Yes, but at least you can get faster updates for smaller dirty areas.

I agree with you, but in this case application will be shown over any window (for touchscreen purposes).

[wysota]

I agree with you, but in this case application will be shown over any window (for touchscreen purposes).

That doesn't mean anything. If you have a widget that contains a button and you push that button, the parent widget will probably receive a paint event as well for the rectangle that contains the push button. So partial paint events may still occur.