Sources

This couldn't have been built without the excellent information available online on C programming in general and MSDOS programming in particular.

• DJGPP VGA access
• Fast access to absolute addresses
• Allegro forums
• Allegro 4.4.2 docs
• How do I use extern to share variables between source files in C? (Stack Overflow)

Also many thanks to Firas Assaad, Katelyn Gadd and Reko Tiira for their help.