7 replies to this topic

[e1will]

I've been giving some thought about what my second game should be once I finish my Duck Attack! homebrew, and I think I might like to tackle porting the XBox Live Arcade game Pac-Man Championship Edition to the Atari 2600.

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.)

--Will

Edited by e1will, Fri Sep 18, 2009 12:36 PM.

[Pixelboy]

Please keep in mind that I'm not very much into Atari 2600 homebrewing when I say this (as most people here know, I'm more a ColecoVision fan), but there have been quite a few Pac-Man games released on the system, both commercially and from homebrewers and hackers. On the other hand, I don't recall anyone ever doing a 2600 version of the Odyssey2's "K.C. Munchkin", and from what I understand of the technical explaination above, I'm thinking perhaps there's an opportunity here to finally have a version of K.C. on the 2600...

Just my two cents.

[youki]

If you do that, i think i 'll buy it! Even i'm really not a huge fan of the VCS . (i'm more Coleco...)

But reading what you described i'm looking foward to see the result.

[Nukey Shay]

e1will, on Fri Sep 18, 2009 12:34 PM, said:

As best I can tell there haven't been any flicker-free Atari Pac-Man ports or clones before,

Jawbreaker and Lock'N'Chase feature no flicker at all.

Quote

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.

I dunno about that...the lack of up/down sprites is part of what earned Frye's port the "honor" of being one of the worst ports ever.

[Lord Helmet]

PMCE on the 2600??

[e1will]

Nukey Shay, on Fri Sep 18, 2009 1:54 PM, said:

I dunno about that...the lack of up/down sprites is part of what earned Frye's port the "honor" of being one of the worst ports ever.

If I can figure out a way to include up/down sprites without introducing flicker, I'll do it.

[Nukey Shay]

I don't mean to sound so negative, but it seems that little detail added a perceived problem of "poor control" to Atari's game. The game doesn't have poor control, it just feels that way. Hacking the game to include upward and downward sprites made a world of difference. If the sprites were omnidirectional (as Lock'N'Chase uses), that also eliminates this perceived problem. So IMO it might be better to use something unique if 4 directions are not possible to display.

Edited by Nukey Shay, Sat Sep 19, 2009 12:38 PM.

[e1will]

Nukey Shay, on Sat Sep 19, 2009 12:36 PM, said:

I don't mean to sound so negative, but it seems that little detail added a perceived problem of "poor control" to Atari's game. The game doesn't have poor control, it just feels that way. Hacking the game to include upward and downward sprites made a world of difference. If the sprites were omnidirectional (as Lock'N'Chase uses), that also eliminates this perceived problem. So IMO it might be better to use something unique if 4 directions are not possible to display.

No, you're right to point out the downside. I was certainly among the millions of people scratching their heads over the lack of up and down sprites in the original. (Although, as I learned more about the hardware/software limitations of the system, it occurred to me that maybe it was that way because Frye had been toying with the idea of making Pac-Man a ball or missile sprite. Obviously, before he decided to add the 'eye.')

The Lock'N'Chase solution to the problem was pretty clever, although I obviously can't do that here. (Missile-ghosts would be pretty darn ugly.)

Honesty, I think it can be done, even if it takes a convoluted mess of code and 20 separate kernels to accomplish it. As a worst-case scenario, it could always be accomplished by further restricting ghost movement, although I'd obviously like to avoid that.

My only "rule" is no flicker. It's a perfectly appropriate technique to use, but with the high-quality Pac-Man versions out there that DO use the technique (i.e. yours!) there seems little point in me adding another version unless it does something that hasn't been done before. I think the gameplay differences between CE and the original are necessary but not sufficient to warrant another version, since there are already really good versions already.

--Will