Mxgui is the Miosix graphis library. It can be found here: https://github.com/fedetft/mxgui
The library needs to be downloaded and configured separately from the kernel.
For boards that already have a display, the correct driver is automatically loaded (but you can add more displays), while if you are attaching a display to a generic development board, you will need to implement the
void mxgui::registerDisplayHook(DisplayManager& dm)
callback to register a display driver.
A tutorial describes how to get started and also how to register a new display.