[Qt-interest] QEventLoop and QEvents

[Frank Hemer]

On Friday 19 February 2010 20:21:07 Eric Clark wrote:
> When I say that it is a little bit of time, it is milliseconds. This is how
> it HAS to work. Without going into great detail, this particular widget is
> a GLWidget. There is an active 3D simulation going on in the widget and
> when you click on the widget, a 3D ray-trace is performed to find the 3D
> object that was clicked on. During the active simulation, there are events
> that happen that cause manipulation of the 3D objects, such as cutting
> holes in the objects, or possibly removing the object from the viewer all
> together. The simulation runs on a separate thread than the GUI and as
> such, it is VERY unsafe to allow the ray-trace to happen while the
> simulation is active. Instead, the 3D viewer reacts to mouse events when it
> repaints. During repainting of the GLWidget, the simulation is temporarily
> paused and any events that occurred between painting will also be
> processed. Believe me, I know what I am doing as far as deferring the
> events. The time between repaints is so fast that no user will ever notice
> the delay in reaction of a mouse click. Not only that, what happens when
> you click on an object is that it gets highlighted in the 3D viewer, this
> highlighting would even be ok if it did take longer than normal, but the
> reaction time now is on the order of milliseconds and no human eye can
> possibly see the delay.
>
> Now that everyone knows what is really going on. I would love for someone
> to answer my question. Is there any way to tell Qt to not delete the event?
> Or do I need to make a copy of the event?

You can catch events (mouse and key) in an QApplication-installed 
eventHandler, store a copy and  post them later.
That works quite well, however be aware of some surprising effects if for ex. 
a Window pops up right before the events get posted.
This will most likely NOT work for other system-internal events though.

Frank