Adafruit has a library at https://github.com/adafruit/Adafruit_FT6206_Library and I've done some things with I2C on the Omega2 at https://github.com/gamer-cndg/omega2-wii-classic-controller using https://docs.onion.io/omega2-docs/i2c-c-library.html. Combine those and you should be able to port the library.