Upgrade gluCylinder from QGLWidget to QOpenGLWidget

To upgrade the 'gluCylinder' function from 'QGLWidget' to 'QOpenGLWidget', you can use the modern OpenGL functions provided by the 'QOpenGLWidget' class. Here's an example of how you can create a cylinder using 'QOpenGLWidget':

1. Subclass 'QOpenGLWidget':

class MyOpenGLWidget : public QOpenGLWidget
{
    //...
};

2. Implement the 'initializeGL' function to set up the OpenGL context:

void MyOpenGLWidget::initializeGL()
{
    // Set the clear color and enable depth testing
    glClearColor(0.0, 0.0, 0.0, 1.0);
    glEnable(GL_DEPTH_TEST);
}

3. Implement the 'paintGL' function to render the cylinder:

void MyOpenGLWidget::paintGL()
{
    // Clear the color and depth buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Set up the camera
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0, width() / height(), 0.1, 100.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

    // Render the cylinder
    glColor3f(1.0, 1.0, 1.0);
    GLUquadric* quadric = gluNewQuadric();
    gluCylinder(quadric, 1.0, 1.0, 2.0, 32, 32);
    gluDeleteQuadric(quadric);
}

4. Finally, create an instance of your 'MyOpenGLWidget' class and set it as the central widget of your main window:

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QMainWindow mainWindow;
    MyOpenGLWidget* glWidget = new MyOpenGLWidget(&mainWindow);
    mainWindow.setCentralWidget(glWidget);
    mainWindow.show();

    return app.exec();
}

Note that the 'gluCylinder' function is part of the legacy OpenGL utility library (GLU). To use it with 'QOpenGLWidget', you need to include the 'glu.h' header and link against the GLU library.