I am experienced programmer for POS machines, including machines that run on Linux. I have been programming for POS for 2 years, and alreday have software modules for printing. The idea is very simple, a font file is used to create a bitmap according to the text to be printed, and then the bitmap is sent to the POS printer using the system APIs.
Although, I need further details on how the data to be printed will be feeded to the POS.