Software-driven Graphics Modes For The Atari 8-bit Computers - SuperIRG

SuperIRG

In 1998, Bill Kendrick created a puzzle video game for the Atari (Gem Drop) which utilized a similar effect, but by using two alternating character sets (fonts) in colored text. (Each character is 4×8 pixels, each pixel being one of 4 colors.) No color palette changes occurred, and ANTIC's display list wasn't altered — only a vertical blank interrupt was used to change the character set. This allowed for approximately 13 colors on the screen. Solid color fields that were based on two actual colors (e.g., dark red created by flickering between red and black) had less artifacting because they could be drawn in a checkerboard fashion. This mode was called SuperIRG. (Normal 4×8 multi-colored text on the Atari is called IRG.)