Linux: disable high dpi scaling on incorrect EDID

If the screen dimensions that are reported by EDID are
unrealistically low disable high dpi scaling.

For this purposes we consider the EDID incorrect if screen is
reported as smaller than 10 cm in width.

Closes #153

main.cpp

@@ -31,23 +31,46 @@ static void consoleMsgHandler(QtMsgType, const QMessageLogContext &, const QStri
 }
 #endif
 
+/* Workarounds for systems on which correct EDID info is not available */
+static inline void _handleDpi(int argc, char *argv[])
+{
+    QGuiApplication tmp(argc, argv);
+    QScreen *primaryScreen = QGuiApplication::primaryScreen();
+    int w = primaryScreen->geometry().width();
+    int h = primaryScreen->geometry().height();
+    int w_mm  = primaryScreen->physicalSize().width();
+    int h_mm = primaryScreen->physicalSize().height();
+
+#ifdef QT_NO_WIDGETS
+    if (h > 720)
+    {
+        qputenv("QT_SCALE_FACTOR", QByteArray::number(h / 720.0, 'f', 2));
+    }
+#else
+    qDebug() << "Displaying on:"
+             << primaryScreen->manufacturer()
+             << primaryScreen->model()
+             << QString::number(w)+"x"+QString::number(h)
+             << QString::number(w_mm)+" mm x "+QString::number(h_mm)+" mm";
+    if (w_mm < 100)
+    {
+        qDebug() << "Physical display dimensions seem unrealistically low. Disabling high DPI scaling";
+        QCoreApplication::setAttribute(Qt::AA_DisableHighDpiScaling);
+    }
+#endif
+}
+
 int main(int argc, char *argv[])
 {
     QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
 #ifdef Q_OS_WIN
     // prefer ANGLE (DirectX) over desktop OpenGL
     QCoreApplication::setAttribute(Qt::AA_UseOpenGLES);
 #endif
+#ifdef Q_OS_LINUX
+    _handleDpi(argc, argv);
+#endif
 #ifdef QT_NO_WIDGETS
-    {
-        QGuiApplication tmp(argc, argv);
-        int h = QGuiApplication::primaryScreen()->geometry().height();
-        if (h > 720)
-        {
-            qputenv("QT_SCALE_FACTOR", QByteArray::number(h / 720.0, 'f', 2));
-        }
-    }
-
     QGuiApplication app(argc, argv);
 #else
     QApplication app(argc, argv);