Dr. Daves Diversions | #DOScember CGA Easter Egg Hunt @DrDavesDiversions | Uploaded December 2021 | Updated October 2024, 13 minutes ago.
In this video we discuss the Color Graphics Adapter (CGA), introduced by IBM in 1981. We'll delve into the video memory segment (frame buffer) layout when in graphics mode(s) and convert from PNG to CGA frame buffer format. Let's see who can build on this information to find the hidden message, or "Easter egg", in this graphical image of the #DOScember logo:

minidraw doscembr.pic (640x200 2-color CGA raw 16KB frame buffer binary)
pastebin.com/nCWZmex9
(After uudecoding, copy this file to A:\SAVED.PIC for minidraw to LOAD it.)

UPDATE 31-DEC-2021: The first person has contacted me and provided evidence that they found the Easter egg!

00:00 intro
00:14 introlude
00:49 background
03:28 the CGA card and the Motorola CRTC IC
06:30 minidraw and the challenge of converting a PNG image for it and CGA frame buffer
13:45 correction: I misspoke by calling it the "modulus" function; I meant "modulo". (Modulus is the divisor in the modulo operation.)
14:52 debugging based on visual "glitch effects", 1st try
19:26 debugging based on visual "glitch effects", 2nd try
23:46 [un]wrapping things up

The script we share in this video is here:

PNGtoCGA640x200
pastebin.com/Hu9nVECu

MiniDraw (assembler DOS application):

minidraw.asm revision 1.10 (white on black for better CGA/TGA compatibility)
pastebin.com/t4Cpzswn

minidraw manual (retyped from 1988 original)
pastebin.com/PN53qtg5

The Easter egg was hidden in 2020, in part 2 of this project:

#DOScember x86 asm & Amiga Bridgeboard
youtube.com/playlist?list=PL2O6RH1Isy65p-cPxMx9HGlq9O_j9iVdx

Related:

CGA Graphics - Not as bad as you thought! (8-bit Guy)
youtube.com/watch?v=niKblgZupOc

Color Graphics Adapter (wikipedia)
en.wikipedia.org/wiki/Color_Graphics_Adapter

Colour Graphics Adapter: Notes (John Elliott's homepage)
seasip.info/VintagePC/cga.html

PC System Programming for developers (See Chapter 10: "Accessing and Programming the Video Cards")
by Tischer, Michael, 1953-
Publication date 1990
archive.org/details/PC_System_Programming

Chapter 10: "Accessing and Programming the Video Cards" (a better scan of this chapter from the book above)
minuszerodegrees.net/misc/PC%20System%20Programming%20-%20Chap%2010.pdf

Motorola 6845
en.wikipedia.org/wiki/Motorola_6845

IBM's CGA Hardware Explained (Nerdly Pleasures)
nerdlypleasures.blogspot.com/2016/05/ibms-cga-hardware-explained.html

IBM PC Color Composite Graphics (Nerdly Pleasures)
nerdlypleasures.blogspot.com/2013/11/ibm-pc-color-composite-graphics.html

The original #DOScember logo was created by DaveJustDave.
youtube.com/user/MrDavejustdave

Glitch Effect: Delving Into The Digital Image Distortion
blog.123rf.com/image-glitch-effect