The most exciting part of it is that I've figured out how to do it with no flicker. Zero. None. Pac-Man and all four ghosts on the screen at the same time, on all frames. Even when there's a bonus item on the screen too. As best I can tell there haven't been any flicker-free Atari Pac-Man ports or clones before, so this should be a pretty neat addition to the roster of 2600 games.
Here's how I'm planning to do it. Pac-Man uses the ball sprite. If you've played Duck Attack! and reached the arcade level (Level 3), you've seen a rough version of the ball-sprite-as-Pac-Man animation in action. The main limitation in using the ball sprite is that Pac-Man can only face left or right (like in the original 2600 Pac-Man port), not up or down, but I think that's a fair trade-off for avoiding the flicker.
The second limitation in using the ball sprite is that the dots and maze walls will need to be yellow too... but only on the horizontal lines where Pac-Man is. This actually works well with the Championship Edition visuals, as the walls change color near where Pac-Man is. The yellow lines would fade to a different color going up or down from Pac-Man. The 4 ghosts will also influence the color of the playfield to match the CE visuals. For example, if the screen contains (from top to bottom) Blinky, Inky, Pac-Man, Pinky and Clyde, the playfield and dots will fade from red to blue to yellow to pink to orange going from top to bottom.
Since Pac-Man is using the ball sprite, that frees the P0 and P1 sprites for the four ghosts. The ghost AI will need to be set up so that Inky and Clyde stay out of Blinky and Pinky's way as they pursue Pac-Man, which is not drastically different from what they do normally. Blinky and Pinky will have basically unconstrained movement (except when a bonus item is on the screen, in which case Pinky will make sure to avoid the horizontal area that Blinky is occupying IF it's the same horizontal area the bonus item is in. It helps that with CE there are tunnels at the top and bottom of the screen; if Blinky is "crowding" any of the ghosts toward the top or bottom of the screen, they can use the tunnels to loop around to ensure Blinky complete freedom of movement without worrying about a scanline collision.
There will be a special, separate kernel for the initial moments of the game, where Pinky, Inky and Clyde are all bouncing up and down in the monster pen. Here, Inky and Clyde will share P0, using the "two copies" NUSIZ0 setting with the color changed in between them. Once Inky starts to leave the monster pen, it will switch to the regular kernel described earlier.
One key thing the CE version has that the "old school" Pac-Man games lack is the background music. Would anyone be interested in designing the musical part of the game? I don't necessarily want the exact music that the XBox version uses; some original music with a similar feel to it would be fantastic.
(And I'm also not planning on actually calling the game "Pac-Man Championship Edition." I haven't decided what yet, but I don't want to use any names that are already trademarked. I figure it's better to err on the side of caution and just call it "Championship Edition" or "C.E." or "Cruise Elroy" or something.)
Edited by e1will, Fri Sep 18, 2009 12:36 PM.