Mega Man 3’s Graphical Glitches, the MMC3 Mapper, and a Bad Development Timeline – Behind the Code

“Is my copy of Mega Man III messed up?”

This question is a common one from those that either have not played the third game in the series or are returning to it after a number of years.

There is a graphical glitch above Shadow Man in the Stage Select screen. A segment of pixels on a single line appear to jitter left and right while the game waits for you to select a boss.

Nothing is wrong with the NES or the cartridge. The game was simply released with some extraneous code that causes the glitch to happen.

In this latest episode of Behind the Code, we’ll take a look at some of the development history behind the third game, talk a bit about the MMC3 Mapper chip and how it can generate an interrupt thanks to counting scanlines, cover some split screen scrolling techniques like those used in Mega Man 3, analyze the graphical glitches seen in the Stage Select and Pause Menu, and finally – perform a few fixes.


Liked it? Take a second to support DisplacedGamers on Patreon!