Black lines on left side of screen

[bradhig]

On most Atari games there were black lines on the left side of the screen. What are they are why couldn't atari get rid of them?

[DEBRO]

There was a bug in the hardware that would produce the black line when the player was repositioned horizontally on the fly. You'll see these in games like Air-Sea Battle, Missle Command, Space Invaders, etc.

 

Atari could have avoided this by doing a HMOVE (horizontal move) on each scan line as Activision did (notice the black bar on the left side of their games) or by timing the HMOVE to hit on cycle count 74.

[landsmarra]

Great technical description of "the comb."

 

I always wondered what caused it, too.

[ElectricTroy]

There was a bug in the hardware that would produce the black line when the player was repositioned horizontally on the fly. You'll see these in games like Air-Sea Battle, Missle Command, Space Invaders, etc.

 

Okay but why is there *several* lines? It looks like a UPC scan code. Your description explains why there's one bar, but why are there multiple bars?

[Room 34]

I think his point was that Activision deliberately designed their games with a black bar on the left side of the screen, to mask out the "comb" (well said) lines that were in fact still there... but invisible as they were black-on-black.

 

Did I get that right?

[DEBRO]

Okay but why is there *several* lines?  It looks like a UPC scan code.  Your description explains why there's one bar, but why are there multiple bars?

 

Whenever the player was repositioned on the fly during the display kernel the black line is drawn. I should say whenever HMOVE was done at the beginning of a scan line (or cycles 76).

 

Look at Missile Command...everytime you see a black line, the programmer called HMOVE which would move the players horizontally. Rob did this every other scan line.

 

Space Invaders and Air Sea Battle don't position the players during the kernel as often as Missile Command so that's why you don't see too many HMOVE lines.

 

Did that make since?

[DEBRO]

I think his point was that Activision deliberately designed their games with a black bar on the left side of the screen, to mask out the "comb" (well said) lines that were in fact still there... but invisible as they were black-on-black.

 

Did I get that right?

[Nukey Shay]

Puzzling why they didn't for more games...doesn't Human Cannonball use that method of "hiding" the lines? That's a pretty early title.

[ATARI TROLL]

Atari Teamed up with Matchbox and came up with a windshield wiper car-tridge series (get it) Car-tridge. Anything you want I can get...the name is Leo Getz ok ok ok....

[ATARI TROLL]

Atari Teamed up with Matchbox and came up with a windshield wiper car-tridge series (get it) Car-tridge. Anything you want I can get...the name is Leo Getz ok ok ok....

[ElectricTroy]

Look at Missile Command...everytime you see a black line, the programmer called HMOVE which would move the players horizontally. Rob did this every other scan line.

 

 

Got it. I always thought the "barcode" on the left of Missile Command looked rather cool. I'd rather deal with that slight imperfection, than the limited playfield of Galaxian.

 

So those lines are in ALL Atari games? (even if not visible)

[Thomas Jentzsch]

So those lines are in ALL Atari games?  (even if not visible)

No!

 

Early simple games like Combat (who never have to horizontally reposition one of the two player objects) and maybe(!) a few very advanced game (who know how to avoid them) do not.

[Room 34]

Just so I understand...

 

This "horizontal repositioning" is used to duplicate on-screen objects, right? Such as the incoming missiles in Missile Command, which often appear as 2 or 3 separate missiles moving in formation. (I use the term "missile" here as a description of the game concept, not referring specifically to the programmatic "missile" object.)

 

This is also how the rows of aliens are created in Space Invaders, right? Or the 2 and 3 lined-up players in Home Run?

 

So what about the multiple planes moving in formation in the jet and bi-plane variations in Combat?

[Nukey Shay]

So those lines are in ALL Atari games?  (even if not visible)

No!

 

Early simple games like Combat (who never have to horizontally reposition one of the two player objects) and maybe(!) a few very advanced game (who know how to avoid them) do not.

 

Would one of those be Alien? I can't see a line on that one

[ZylonBane]

This "horizontal repositioning" is used to duplicate on-screen objects, right?

No. 2600 players and missiles technically extend all the way from the top to the bottom of the screen. Horizontal repositioning (don't put it in quotes-- it's not a technical term, it's a literal description of what's happening) just moves the player to different horizontal positions as it goes down the screen, allowing the appearance of multiple (non-overlapping) objects using a single player. This is why so many 2600 games have horizontal strips of moving objects.

 

It also sounds like you're confusing the issue with games that use the duplication registers (which gives the three-in-a-row fighter jets in Combat, for example).

 

It is possible to horizontally reposition a sprite multiple times on the same scanline, but this is deep mojo that you shouldn't worry about just yet.

[MegaManFan]

Anybody ever figure out a solution to the lines on the lefthand side of the screen in Jr. Pac-Man?

[Room 34]

(don't put it in quotes-- it's not a technical term, it's a literal description of what's happening)

 

I put it in quotes because I was quoting someone.

 

It also sounds like you're confusing the issue with games that use the duplication registers (which gives the three-in-a-row fighter jets in Combat, for example).

 

Yes, you are right.

 

I still don't quite understand what horizontal repositioning is, then. Can you give me a specific example, from a specific game?

 

but this is deep mojo that you shouldn't worry about just yet.

 

Cute. I am pretty stupid, so be sure to dumb down your answers accordingly.

[Thomas Jentzsch]

Would one of those be Alien?  I can't see a line on that one

Alien produces those blank lines on every line (the left border is smaller than the right one). This is the trick Activision used too.

[Thomas Jentzsch]

I still don't quite understand what horizontal repositioning is, then.  Can you give me a specific example, from a specific game?

Example: All enemy objects in River Raid, the cars in Enduro, the objects in Sky Jinks, M*A*SH* etc (or Berzerk!). And all games with a Frogger layout (Freeway, Space Treat, Grand Prix). Or the ghosts in in Mr Pac Man and Jr Pac Man etc.

 

Since they don't have the same horizontal position the programmer has to reposition each new object.

[ZylonBane]

Cute. I am pretty stupid, so be sure to dumb down your answers accordingly.

I wasn't attempting to be cute. Repositioning players on the same scan line is scary stuff that's not for the faint of heart. Just accept that it can be done... sometimes... when the phase of the moon is right.

 

Other blatant examples of player reuse via on-the-fly horizontal repositioning-- Turmoil, Demons to Diamonds, A-Team, Riddle of the Sphinx, Xevious, Air-Sea Battle, Atlantis.

 

The ghosts in Ms. and Jr. Pac-Man aren't good examples of this, because those games also do sprite multiplexing, which is a whole other technique that sits on top of what we're discussing.