I have made several programs that I use to generate these previews. One for generating the 3d boxes and another program that combines all the images together and finally one to create the gamelist.xml needed by emulationstation.
Your programs to create images are great, but gamelist.xml for megadrive was not what i need. It seems to have the same release date for all games. I prefer to use scrapper for windows (uses hash instead of rom filename to match game) on my roms folder, which creates better gamelist with more info. Then search-replace with null <description>.*?</description> in notepad++ to delete text unused in my theme (work in progress). It looks like this for now: https://www.youtube.com/watch?v=v6tVkgb-V24 So… looking forward for your next previews 🙂