started qt6 migration

src/OpenMesh/Apps/ProgViewer/progviewer.cc

@@ -51,15 +51,20 @@
 #include <OpenMesh/Apps/ProgViewer/ProgViewerWidget.hh>
 #include <QString>
 #include <QApplication>
-#include <QGLWidget>
-
+#if QT_VERSION_MAJOR > 5
+#include <QOpenGLContext>
+#endif
 
 int main(int argc, char **argv)
 {
   // OpenGL check
   QApplication app(argc,argv);
 
+#if QT_VERSION_MAJOR < 6
   if ( !QGLFormat::hasOpenGL() ) {
+#else
+  if ( QOpenGLContext::openGLModuleType() != QOpenGLContext::LibGL ) {
+#endif
     std::cerr << "This system has no OpenGL support.\n";
     return -1;
   }