Q: Qt - [c++] QDialog gets repainted when overlay dialog closes

[kevin_d]

Hello Qt Forum!

I am manually drawing a background (with lines and polygons) on a dialog, which is rendered at the paintEvent(QPaintEvent *) method.
Then, an additional dialog is shown, partially overlying on the background-dialog.
Whenever such an overlay-dialog closes, the background dialog gets fully visible, and redraws all the background (with hundrets of polygons) again.

This causes a delay when showing, hiding overlay dialogs.

Is there a possibility, to 'cache' the drawn background area, so it needs to be rendered only once?

If i suppress all following paintEvents, all the manually painting gets lost and the dialog only shows the background color ...

Thanks, cheers, kevind_d

[kevin_d]

Is it possible to prevent the dialog from being repainted and keep the initial graphic contents?

cheers, kevin

[Christian Ehrlicher]

When the os asks to redraw something you have to do it - noone is doing caching here (how should it work though - how should someone except you know that nothing has changed in between)
The only way I see is to cache the whole painting in a QImage and only draw the QImage in paintEvent()

[kevin_d]

Hello!

Yes, i was hoping for a hack for this :-)

Thanks, solved

[kevin_d]

It still seems odd, that the dialog needs repainting, when it is not resized ...

[JonB]

@kevin_d It needs repainting because it was (partially) obscured and now needs to be shown fully again, normal windows behaviour.....