We have looked into your project. We found that if we remove the code “QApplication app(args, argv);” , the Aspose.Cells library will work fine. We conclude that since Aspose.Cells library calls GDIPlus to realize drawing functionality, and QT GUI also call GDI, so, when you call “QApplication app(args, argv);” this code may execute some initialization and settings work which have an impact to Aspose.Cells drawing functions and causes a different result compare to running in Visual Studio.
To prove our inference, we modify your project and just call a simple GDIPlus function, which returns different result before and after removing “QApplication app(args, argv);”. So, we think you should modify your code in QT side accordingly. Because, we are not familiar with QT GUI module much, so we cannot give you more professional advice. If you still do not know how to do, you can rise a topic in forum.qt.io.