Different behaviors of GLWidget,Widget,Canvas,Scene when obscured by other windows

[wysota]

but what exactly is the problem?

[yektaayduk]

The problem is: I cant update the Zoom window entirely at once ,because it takes too long ,
other threads which requesting data from an signal processing board(actually from the kernel module of the same board kernel buffer overflows before I read it) and forwarding data via ethernet loosing data .
That's way I update the zoom window in time ,in small parts.Refreshing an erased part of the window obscured by another window, by my functions will take again too long.I need a solution without my effort,like i observed in opengl case (it recovers without calling my code ).Is this unique to opengl?

[wysota]

This is an X11 issue. I think that using extensions such as Damage, you could avoid redraws, but I'm not sure of that. I suggest you cache the result of the last draw in a pixmap and simply redraw the pixmap when the paint event comes in. Just make sure to regenerate the pixmap when the contents of the widget change.

[yektaayduk]

Thank You wysota

I will try .