Free Masters of Doom by David Kushner Page B

redraw only the things that actually change? That way, the scrolling effect could
     be rendered more quickly. He imagined looking at a computer screen that showed a character
     running to the right underneath a big blue sky. If that character ran far enough,
     a white puffy cloud would eventually pass from off screen over his head. The computer
     created this effect in a very crude way. It would redraw every little blue pixel on
     the entire screen, starting at the top left corner and making its way over and down,
     one pixel at a time, even though the only thing that was changing in the sky was the
     white puffy cloud. The computer couldn’t intuit a shortcut to this drudgery just because
     a shortcut made sense. So Carmack did the next best thing. He tricked it into performing
     more efficiently. Carmack wrote some code that duped the computer into thinking that,
     for example, the seventh tile from the left was in fact the first tile on the screen.
     This way the computer would begin drawing right where Carmack wanted it to. Instead
     of spitting out dozens of little blue pixels on the way over to the cloud, the computer
     could
start
with the cloud itself. To make sure the player felt the effect of smooth movement,
     Carmack added one other touch, instructing the computer to draw an extra strip of
     blue tile outside the right edge of the screen and store it in its memory for when
     the player moved in that direction. Because the tiles were in memory, they could be
     quickly thrown up on the screen without having to be redrawn. Carmack called the process
     “adaptive tile refresh.”
    In lay terms, as Tom immediately understood, this meant one thing:
They could do Super Mario Brothers 3 on a PC!
Nobody, no one, nowhere had made the PC do this. And now they could do it, right
     here, right now, take their all-time favorite video game and hack it together so it
     could work on the computer. It was almost a revolutionary act of subversion, he thought,
     especially considering Nintendo’s stronghold on its own platform. There was no way
     to, say, copy a Nintendo game onto a PC as one would tape an album. But now they could
     replicate it tile for tile, blip for blip. It was the ultimate hack.
    “Let’s do it!” Tom said. “Let’s make the first level of Super Mario tonight!”
    He fired up Super Mario on the TV in the Gamer’s Edge office and started to play.
     Then he opened up the tile editor that they had running on their PCs. Like someone
     copying a famous painting, he re-created every little tile of the first level of Super
     Mario on the PC, hitting pause on the Nintendo machine to freeze the action. He included
     everything—the gold coins, the puffy white clouds; the only thing he changed was the
     character. Rather than re-create Mario, he used the stock graphics they had of Dangerous
     Dave. Meanwhile, Carmack was optimizing his side-scrolling code, implementing the
     features of the game that Tom barked out while he was pausing and playing. Dozens
     of Diet Cokes later, they finished the first level. It was 5:30 a.m. Carmack and Tom
     saved the level to a disk, set it on Romero’s desk, and went home to sleep.
    Romero came in the next morning at ten and found the floppy disk on his keyboard with
     a Post-it note that read merely, “Type DAVE2.” It was in Tom’s handwriting. Romero
     popped the disk into his PC and typed in the file location. The screen went black.
     Then it refreshed with the words
    DANGEROUS
DAVE
IN
“COPYRIGHT INFRINGEMENT”
    On one side of the words was a portrait of Dangerous Dave in his red baseball cap
     and green T-shirt. On the other was a dour looking judge with a white wig, brandishing
     a gavel. Romero hit the spacebar to see what would come next. There it was, the familiar
     milieu of Super Mario Brothers 3: pale blue sky, the puffy white clouds, the bushy
     green shrubs, the animated tiles with little question marks rolling over their sides
     and, strangely, his