In MyGLWindow example

• Constructor definition doesn't contain the qualified class name
  EXPECTED:

  MyGLWindow::MyGLWindow(QScreen *screen) { ... }
  

  ACTUAL:

  MyGLWindow(QScreen *screen) { ... }
  

• "QOpenGLWidget" is not a nonstatic data member or base class of class "MyGLWindow"
  ACTUAL:

  class MyGLWindow : public QWindow, protected QOpenGLFunctions
  {
      Q_OBJECT
  public:
      explicit MyGLWindow(QScreen *screen = nullptr);
  
      ...
  };
  
  MyGLWindow(QScreen *screen)
    : QWindow(screen), QOpenGLWidget(parent)
  {
      ...
  }