Very nice game. A couple of links with information on programming graphics in DOS, maybe not so much EGA, but it might have you interest anyway:
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You know, the Asphyxias Tutorials was what really got me started on VGA programming back in the days. Those were my bibles! I studied all of them so much as a teen, and was what got me into demo coding. One day as a teen i actually tried calling his phone number, which was in one of the tutorials, but when he finally picked up the phone i was just too shy to say anything, and just hung up! :) I have the physical Abrash book btw! not cheap and easy to get by these days i can tell you! It was just so much cooler having the physical book i could look in, while i developed the game. That made it so much more authentic, instead of sitting with a laptop and a PDF besides my 486.