How was "Lock N Chase" possible on the 2600?

[rhindlethereddragon]

In 1981, PAC MAN was released for the Atari 2600, and all of the ghosts flickered so badly they looked "transparent"

 

In the same year, Mattell released "Lock N Chase" to compete with Pac Man on the Atari 2600. In a stark contrast to Pac Man, all of the sprites in "Lock and chase" were SOLID - not even a HINT of "flicker".

 

What did Mattell do with Lock and Chase that Atari didn't do with Pac Man ?

[Thomas Jentzsch]

Play on an emulator and disable the sprites.

Watch the pattern of the vertical movement.

 

[+Random Terrain]

Check out this thread:

 

Why no flicker in Lock 'N' Chase?

[maiki]

I noticed that too. No flicker in Lock 'n' Chase at all. Excellent job how to properly design a game on a limited system. I don't have patience to read that thread but I guess it is a combination of special sprite multiplexing tricks and intelligent placing of the objects together.

[+Random Terrain]

I noticed that too. No flicker in Lock 'n' Chase at all. Excellent job how to properly design a game on a limited system. I don't have patience to read that thread but I guess it is a combination of special sprite multiplexing tricks and intelligent placing of the objects together.

 

You don't have to read the whole thread. The following 2 posts are pretty much all you need:

 

It looks like how it works is player 0 is your player. Missile 0 is the bonus thing in the middle and the thing at the top.

 

Player 1 and missile 1 both are set to look the same. Missile 1 has its width and position adjusted to assume that particular shape.

 

It looks like Player 1 and missile 1 are displayed twice per frame and are not allowed to overlap each other vertically. I'd have to play it to know for sure.

 

M-Network was known for abusing the missiles to fool people into thinking they were regular players. Super Challenge Football is a more famous example since it has an animation cycle also.

 

I was always intrigued by this. That's what the technical impetus was behind Death Derby. But it turned out tricky enough that only Thomas J. was about to make it happen without introducing tearing effects in the sprites.

 

M-Network didn't get enough credit for their 2600 work. I'm sure a disassembly would reveal some very clever kernel coding here.

 

To use something like this in batari Basic would require a custom kernel.

 

If you didn't need the missiles for projectiles, it's a good way to go.

 

Besides Lock n Chase with its vertical separation limitation, the DD kernel provides full freedom of movement for all 4 objects plus the 32x11 striped playfield bitmap and an independently colored ball that is limited to either a straight line or a dash that has to be inbetween the playfield rows.

 

I'm sure other games could be built with that.

 

If you hack the game so to make the player and missile shapes distinct (see attachment), you'll notice that the game can freely switch between using players or missiles for the enemies. I didn't look into the code to see how the 'zones' are defined, but each enemy does have full use of the screen unlike e.g. Mousetrap.

 

Here is supercat's hack:

 

lock1.bin

[maiki]

Player 1 and missile 1 both are set to look the same. Missile 1 has its width and position adjusted to assume that particular shape.

 

Interesting to see they actually used either an 8-bit object or a 1-bit object for the same graphics (?)...

 

 

If you hack the game so to make the player and missile shapes distinct (see attachment), you'll notice that the game can freely switch between using players or missiles for the enemies.

 

Why is that implemented?

Edited December 28, 2011 by maiki

[accousticguitar]

If you hack the game so to make the player and missile shapes distinct (see attachment), you'll notice that the game can freely switch between using players or missiles for the enemies.

 

Why is that implemented?

To eliminate flicker would be my guess. Genius, actually.

[maiki]

To eliminate flicker would be my guess. Genius, actually.

 

But where is the flicker when you are using player0 (player) vs player1 / missile1 (enemies)...

Edited December 29, 2011 by maiki

[Skylark68]

I know some folks don't care for M Network games, but they had some top notch programmers. Most of their games are on my favorites list.

[accousticguitar]

To eliminate flicker would be my guess. Genius, actually.

 

But where is the flicker when you are using player0 (player) vs player1 / missile1 (enemies)...

I'm not sure what you are asking.

[maiki]

To eliminate flicker would be my guess. Genius, actually.

 

But where is the flicker when you are using player0 (player) vs player1 / missile1 (enemies)...

I'm not sure what you are asking.

 

How is swapping between player1/missile1 related to reducing flicker? There is no flicker when displaying both of them on a scanline anyway.

Edited December 31, 2011 by maiki

[Thomas Jentzsch]

How is swapping between player1/missile1 related to reducing flicker?

It doesn't.

 

But if you watch the vertical order of the objects, it is always player, missile, player, missile. That makes coding the kernel easier, but requires some extra code for swapping outside the kernel.

Edited December 31, 2011 by Thomas Jentzsch

[accousticguitar]

I guess I misunderstood what was going on. If you could swap player1 with player2 that could conceivably eliminate flicker.