[Qt] Enable automatic application scaling for recent Qt versions on W…

…indows to deal with HiDPI displays

This should save users the hassle to set environment variable QT_AUTO_SCREEN_SCALE_FACTOR to achieve the same effect.

avidemux/qt4/ADM_jobs/src/ADM_jobControl.cpp

@@ -207,6 +207,9 @@ bool        jobWindow::popup(const char *errorMessage)
 bool jobRun(int ac,char **av)
 {
     initTranslator();
+#if defined(_WIN32) && QT_VERSION >= QT_VERSION_CHECK(5,11,0)
+    QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+#endif
     QApplication *app=new QApplication(ac,av,0);
     Q_INIT_RESOURCE(jobs);
     loadTranslator();

avidemux/qt4/ADM_userInterfaces/ADM_gui/Q_gui2.cpp

@@ -1647,7 +1647,11 @@ int UI_Init(int nargc, char **nargv)
     global_argc=nargc;
     global_argv=nargv;
     ADM_renderLibInit(&UI_Hooks);
-
+#if defined(_WIN32) && QT_VERSION >= QT_VERSION_CHECK(5,11,0)
+    // Despite HiDPI scaling being supported from Qt 5.6 on, important aspects
+    // like OpenGL support were fixed only in much later versions.
+    QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+#endif
     myApplication=new myQApplication (global_argc, global_argv);
     myApplication->connect(myApplication, SIGNAL(lastWindowClosed()), myApplication, SLOT(quit()));
     myApplication->connect(myApplication, SIGNAL(aboutToQuit()), myApplication, SLOT(cleanup()));