Use QOpenGLWindow with the frameSwapped signal. This is my example with Qt 6.7 that prints delta time to the console:

main.cpp

Qt Code: 
  1. #include <QtCore/QElapsedTimer>
  2. #include <QtGui/QOpenGLFunctions>
  3. #include <QtGui/QSurfaceFormat>
  4. #include <QtOpenGL/QOpenGLWindow>
  5. #include <QtWidgets/QApplication>
  6.  
  7. class OpenGLWindow : public QOpenGLWindow, private QOpenGLFunctions
  8. {
  9. public:
  10.  
  11.     OpenGLWindow()
  12.     {
  13.         setTitle("OpenGL ES 2.0, Qt6, C++");
  14.         resize(380, 380);
  15.  
  16.         QSurfaceFormat surfaceFormat;
  17.         surfaceFormat.setSwapInterval(1);
  18.         connect(this, SIGNAL(frameSwapped()), this, SLOT(update()));
  19.         setFormat(surfaceFormat);
  20.     }
  21.  
  22. private:
  23.  
  24.     void initializeGL() override
  25.     {
  26.         initializeOpenGLFunctions();
  27.         glClearColor(0.2f, 0.2f, 0.2f, 1.f);
  28.         m_elapsedTimer.start();
  29.     }
  30.  
  31.     void resizeGL(int w, int h) override
  32.     {
  33.         glViewport(0, 0, w, h);
  34.     }
  35.  
  36.     void paintGL() override
  37.     {
  38.         float dt = m_elapsedTimer.elapsed() / 1000.f;
  39.         m_elapsedTimer.restart();
  40.         qDebug() << dt;
  41.         glClear(GL_COLOR_BUFFER_BIT);
  42.     }
  43.  
  44. private:
  45.     QElapsedTimer m_elapsedTimer;
  46. };
  47.  
  48. int main(int argc, char *argv[])
  49. {
  50.     QApplication::setAttribute(Qt::ApplicationAttribute::AA_UseDesktopOpenGL);
  51.     QApplication app(argc, argv);
  52.     OpenGLWindow w;
  53.     w.show();
  54.     return app.exec();
  55. }
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