Question

I am trying to write an OpenGL visualization program for some scientific data using Qt. I would like to be able to use my existing program unchanged and simply be able to call the glwidget and tell it to update the data at the end of each time step. However in order to run a Qt program it appears you have to use QApplication and then qt.run() which blocks the cpu.

Here is the pseudo code

main()

{
    ..set up stuff
    myVisualizer = new myGLWidget();

    for(int i=0;i<1000;i++)
    {
        ..do calculations
        myVisualizer.update(new data)
    }
}   

I realize that I could put all of my existing code in to a QThread and have it send a signal whenever it is done to connect to an update. It would just be easier this way. Does anybody have an idea how to solve this?

Answer 1

If you really don’t want to investigate the threaded solution, which would be nicer all around, you can use the special-case timeout with 0. Basically, when you run a timer with a timeout of 0, it runs the appropriate code after processing the events that are currently on the event queue. So, you could set up something like this:

class MyDialog : public QDialog
{
    Q_OBJECT
public:
    MyDialog()
    {
        m_step = 0;
        QTimer::singleShot( 0, this, SLOT( Process() ) );
    }

public slots:
    void Process() 
    {
        // do calculations
        m_step++;
        QTimer::singleShot( 0, this, SLOT( Redraw() ) );
        if ( m_step != 1000 )
            QTimer::singleShot( 0, this, SLOT( Process() ) );
    }

    void Redraw() { // do redrawing code here }

private:
    int m_steps;
};

And then combine it with the Qt-proper main code:

int main( int argc, char** argv )
{
    QApplication app( argc, argv );
    MyDialog dialog;
    dialog.show();
    return ( app.exec() );
}