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How Connect Two Timed Methods in sequence

  • Hi!
    I have a simple doubt here , and i dont know if it´s possible with Qt:

    I have a simple OpelGL Window where i use a Render method to update the rendering using a timer as below:

        connect(this, SIGNAL(widthChanged (int)), this, SLOT(resizeGl()));
        connect(this, SIGNAL(heightChanged(int)), this, SLOT(resizeGl()));
        timer = new QTimer(this);
        connect(timer, SIGNAL(timeout()), this, SLOT(RenderScene()));

    My doubt is:
    It´s possible i connect another method like "UpdateScene" slot that be executed only after RenderScene finish it´s job?

    Any help will be much appreciated becouse i´m having syncronization issues between the rendering being performed in the screen and the data being updated on the aplication, since the GPU´s are rendering in threads.

    Kind Regards.

  • Hi @wwolff

    I might be missing the point of what you're asking, but as slots are just regular functions, you can always call one from the other, eg:

    void MyClass::RenderScene() {
        // do whatever RenderScene does.
        UpdateScene(); // invoke the UpdateScene slot directly.

    If you're bothered by the added coupling, you can emit your own signal as a go-between, eg:

    void MyClass::MyClas(...) {
        connect(this, SIGNAL(sceneRendered()), this, SLOT(UpdateScene()));
        // the rest of your sample code from above here...
    void MyClass::RenderScene() {
        // do whatever RenderScene does.
        emit sceneRendered();

    Since you've specifically mentioned using threads, you probably want to use the signal/slot separation, because that allows you to use Qt's queued connections (or other connection types as appropriate) if signalling from one thread, to another's slot... have a read of Signals and Slots Across Threads.


  • Thanks so much!
    This is exactly what´s i´m looking for (A way to fire up a signal to inform that my UpdateScene Method need be executed).

    I will try it!

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