Code for screen color changing

[CrazyChris]

I'm not a programmer, just an Atari 2600 enthusiast.

 

On the original Atari brand 2600 games, after a few minutes when

the game was over the screen would start changing random

colors. Possibly to prevent screen burn in?

 

Did Atari have their own code to do this?

 

Wouldn't it be cool if this was available to programmers

who want to make their homebrews more authentic.

 

Chris

Edited June 17, 2007 by CrazyChris

[SeaGtGruff]

I'm not a programmer, just an Atari 2600 enthusiast.

 

On the original Atari brand 2600 games, after a few minutes when

the game was over the screen would start changing random

colors. Possibly to prevent screen burn in?

 

Did Atari have their own code to do this?

 

Wouldn't it be cool if this was available to programmers

who want to make their homebrews more authentic.

 

Chris

I think Atari did have a standardized code technique for this, and I think it's been discussed on the Stella list. You don't have to use that specific method, though; you can just change the color registers every so often if no input has occurred.

 

Michael

[Nukey Shay]

True that. Many games stored a dedicated color table in RAM...which is pretty wasteful if the game you are developing has cycles to spare whenever color values are stored to the registers (or at least storing them to temp ram).

 

Just search for "attract mode" in a commented disassembly or source code. It's basically taking the original color fetched from a table, EORing that with an updated timer, then using AND to trim off bits according to the B&W switch status (AND #$FF = color, AND #$0F = B&W).