c++ - Qt Painter outside paintEvent - impossible - workaround?

Question

So it appears that Qt4 doesn't let you draw on windows outside of a paint event. I have a lot of code that expects to be able to in order to draw rubber band lines (generic drawing code for a particular, proprietary interface that I then implement in the given UI). I've read about the pixmap method, it would be a lot of work and I don't think it's really what I want.

Is there a workaround that allows me to do what I want anyway? I just need to draw XOR bands on the screen.

Tried the WA_PaintOutsidePaintEvent flag. Then I saw the bit that says it doesn't work on Windows.

Answer 1

In modern compositing desktops window painting needs to be synchronized by the window manager so that the alpha blending and other effects can be applied, in order, to the correct back buffers - the result of which is then flipped onto the screen to allow tear-free window animations.

Invoking painting operations out-of-band of this process - while supported for legacy reasons on the underlying platforms - would subvert this process and cause a number of very non optimal code paths to be executed.

Basically, when you have painting to do on a window: Call the invalidate function to schedule the painting soon, and paint during the paint event.