Improve NaviCube font matching on linux

src/Gui/MainWindow.cpp

@@ -347,6 +347,17 @@ MainWindow::MainWindow(QWidget * parent, Qt::WindowFlags f)
 
     // accept drops on the window, get handled in dropEvent, dragEnterEvent
     setAcceptDrops(true);
+
+    // setup font substitutions for NaviCube
+    // Helvetica usually gives good enough results on mac & linux
+    // in rare cases Helvetica matches a bad font on linux
+    // Nimbus Sans Narrow and Open Sans Condensed added as fallback
+    // Bahnschrift is a condensed font available on windows versions since 2017
+    // Arial added as fallback for older version
+    auto substitutions = QStringLiteral("Bahnschrift,Helvetica,Nimbus Sans Narrow,Open Sans Condensed,Arial,Sans");
+    auto family = QStringLiteral("FreeCAD NaviCube");
+    QFont::insertSubstitutions(family, substitutions.split(QLatin1Char(',')));
+
     statusBar()->showMessage(tr("Ready"), 2001);
 }