Adjusting horizontal position

[doctorclu]

Hello, currently trying to adjust the vertical hold/position of Atari 2600 games, say if you wanted to move the game field down a few inches.  Was curious if there is anyone that could show me how you could adjust that?

[Thomas Jentzsch]

Where?

• On TV or monitors? I doubt modern, digital devices offer any options.
• In Stella? RTFM!  
• ...?

 

BTW: Vertical or horizontal?

Edited May 26 by Thomas Jentzsch

[+splendidnut]

If you're hacking the game, one thing you could do is look for places where the game stores to the RIOT timer... TIM64T specifically.  Games usually (not always) use the RIOT timer to handle timing the VBlank / Overscan regions.  If the value stored falls between $20..$3F, it's probably the value for the VBlank/Overscan region above or below the playfield.

[doctorclu]

23 hours ago, splendidnut said:

If you're hacking the game, one thing you could do is look for places where the game stores to the RIOT timer... TIM64T specifically.  Games usually (not always) use the RIOT timer to handle timing the VBlank / Overscan regions.  If the value stored falls between $20..$3F, it's probably the value for the VBlank/Overscan region above or below the playfield.

Some good pointers and some good commands I can convert into hex and search for.  Thanks!

23 hours ago, Thomas Jentzsch said:

Where?

• On TV or monitors? I doubt modern, digital devices offer any options.
• In Stella? RTFM!  
• ...?

 

BTW: Vertical or horizontal?

 

That brought up some interesting questions to me, mostly the TV, monitor, or emulator question.  So a bit of back story, currently polishing up a demo of the VirtualVCS for the Jaguar which is primarily a 6507 emulator using the Jaguar's Tom chip.   While the player missile graphics are not working yet there were other 2600 games that used other hit detection.   My immediate fokus is Skydiver.

 

As you can see in this video the gameplay tends to ride up a few inches in Virtual VCS...

 

though in earlier runs of the game the game field looked pretty good... different types of Jags?   Different monitors?   Your question got me wondering on that.

 

But that is why I wanted to see if we could lower the playfield a few inches and see if that straightens out this game and a few other games.

 

To date Skydiver and Space Battle are my two favorite 2600 games that work (at least enough) under VirtualVCS on the Jag.

 

[JetSetIlly]

18 minutes ago, doctorclu said:

But that is why I wanted to see if we could lower the playfield a few inches and see if that straightens out this game and a few other games.

 

To date Skydiver and Space Battle are my two favorite 2600 games that work (at least enough) under VirtualVCS on the Jag.

 

That looks to me like VirtualVCS is not handling VBLANK correctly.

 

Skydiver doesn't set VBLANK until scanline 259. However, using the flag icon as a guide, it looks like VBLANK is starting at 232.

 

Because the black area is visible at the bottom of the screen, I'm guessing that VirtualVCS is correctly "sizing" the screen by using the VBLANK signal. But is incorrectly assuming VBLANK is enabled on scanline 232 when choosing what colour to output to screen.