QTimer ->start(0) + OpenGL + resize/move window => crash

[anthibug]

Hi,

I've got an issue with OpenGL.
I've got a QMainWindow (loaded from a .ui), that include a QGLWidget, well in fact an instance of a personnalize class that inherits from QGLWidget, ...

Actually I'm migrating an SDL+OpenGL application into a QT 4.4 + OpenGL app
It's kind of a 3D cloud points viewer.

Ok by now everything works, I see the scene, I can interact with it (keyboard, mouse), but it's not perfect.

In the first time my idea was to do like in SDL : an infinit while(true) loop.
I managed to do that with this code in constructor :

connect(&qTimerRedraw, SIGNAL(timeout()), this, SLOT(dessiner()));
qTimerRedraw.start(0); // CPU = 100%

connect(&qTimerRedraw, SIGNAL(timeout()), this, SLOT(dessiner()));
qTimerRedraw.start(0); // CPU = 100%

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As the comment explains, it's pretty obvious that one core is going to be at 100% because of the QTimer interval set to 0. And I really don't care if so, because I know how to slow down the framerate in order to reduce the CPU usage. (I could also see the FPS in live).
It's great, very fluid with key events (stay pressed, release, ...).

The problem is that : my application is sometimes crashing when I move the window or when I resize it. Precisely, the crash occurs when i release the mouse button. Why does this crash appears errraticaly ?
I tried to QDebug ResizeGL() without success.

After I realize the bug was due to the infinite signal<->slot loop, I had a second idea : pause the timer during the "work time" :

void gldrawer::paintGL()
{
    qTimerRedraw.stop(0); // wait before the end
 
    // paint job ... (heavy work)
 
    qTimerRedraw.start(0); // restart
}

void gldrawer::paintGL()
{
    qTimerRedraw.stop(0); // wait before the end

    // paint job ... (heavy work)

    qTimerRedraw.start(0); // restart
}

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This might be a good idea with a long "work time" but it doesn't resolve my issue.

My third idea was a different approch : during my research I discover that lots of example works in another way to handle user interaction. The scene is refreshed only when a user interaction leads to a repaint (keyboard or mouse event typically).
That is a very good idea because you do not need to do an infinite loop (100%CPU) so it was solving my problem in 2 ways :
-no loop => no crash when moving or resizing
-my application does not have animations, it's only when the user interact that I have to redraw

So I made modifications to my code, but now there is another problem : keys events.
-I can't use modifiers like SHIFT, ALT, ...
->I can't check the modifiers during a keyPressEvent call
->It stops the other key :
i see keyReleaseEvent calls even if i stay pressed, what the ??!
-When you constantly press a key, the reaction is like in a text application : small delay before the event is fire continously

In the two solutions, the application is fluid when the user keeps the key down, so that's cool. But in both cases, I've got glitches...
What is the best thing to do ? How can I fix my problems ?

Do I need to post some code ?

Thanks!