- Switch to using QGuiApplication::primaryScreen for screen size (desktopwidget is deprecated)

- connect() to the geometryChanged and orientationChanged screen calls to detect changes

src/mainwindow.cpp

@@ -15,7 +15,8 @@
 #include <QRect>
 #include <QGraphicsScene>
 #include <QGraphicsPixmapItem>
-#include <QDesktopWidget>
+#include <QApplication>
+#include <QScreen>
 #include <sstream>
 
 MainWindow::MainWindow(QWidget *parent) :
@@ -34,6 +35,16 @@ MainWindow::MainWindow(QWidget *parent) :
     label->setAlignment(Qt::AlignHCenter | Qt::AlignVCenter);
     update();
 
+    QScreen* screen = QGuiApplication::primaryScreen();
+    if (screen)
+    {
+      connect(screen, SIGNAL(geometryChanged(QRect)), this, SLOT(checkWindowSize()));
+      connect(screen, SIGNAL(orientationChanged(Qt::ScreenOrientation)), this, SLOT(checkWindowSize()));
+      screen->setOrientationUpdateMask(Qt::LandscapeOrientation |
+                                      Qt::PortraitOrientation |
+                                      Qt::InvertedLandscapeOrientation |
+                                      Qt::InvertedPortraitOrientation);
+    }
 }
 
 MainWindow::~MainWindow()
@@ -107,9 +118,11 @@ bool MainWindow::event(QEvent* event)
 void MainWindow::resizeEvent(QResizeEvent* event)
 {
   QMainWindow::resizeEvent(event);
-  // the window size in this event may not match the monitor size, so use QDesktopWidget to find the true monitor size
-  QDesktopWidget desktop;
-  QSize screenSize = desktop.screenGeometry(this).size();
+  // the window size in this event may not match the monitor size, so use QGuiApplication to find the true monitor size
+  QScreen *screen = QGuiApplication::primaryScreen();
+  if (screen != nullptr)
+  {
+    QSize screenSize = screen->geometry().size();
     bool isLandscape = screenSize.width() > screenSize.height();
     if (imageAspectMatchesMonitor)
     {
@@ -120,25 +133,32 @@ void MainWindow::resizeEvent(QResizeEvent* event)
       std::cout << "Got resize:" << this << " " << screenSize.width() << "," << screenSize.height() << " , is landscape? " << (isLandscape ? "y" : "n") << std::endl;
     }
     updateImage(true);
-  QTimer::singleShot(5, this, SLOT(checkWindowSize()));
     if(lastScreenSize != screenSize && switcher != nullptr)
     {
       lastScreenSize = screenSize;
+      if(debugMode)
+      {
+        std::cout << "Updating image due to resize" << std::endl;
+      }
       switcher->updateImage();
     }
+  }
 }
 
 void MainWindow::checkWindowSize()
 {
-  QDesktopWidget desktop;
-  QRect screenSize = desktop.screenGeometry(this);
-  if(size() != screenSize.size())
+  QScreen *screen = QGuiApplication::primaryScreen();
+  if (screen != nullptr)
+  {
+    QSize screenSize = screen->geometry().size();
+    if(size() != screenSize)
     {
       if(debugMode)
       {
         std::cout << "Resizing Window" << screenSize.width() << "," << screenSize.height() << std::endl;
       }
-    setFixedSize(screenSize.size());
+      setFixedSize(screenSize);
+    }
   }
 }