How did he do it! Yars Revenge

[Brian's Man Cave]

Hey,

 

Just thought this needs a discussion. How did Professor Ports make that colorful field zone in the middle??  

 

 

[carlsson]

Machine code, I believe. Note that each cell still has one foreground and background, just that both pattern and foreground changes every frame (?) making it look like many colors at once. Usually that kind of flickering would not be preferred but it works great here.

[+DZ-Jay]

3 hours ago, carlsson said:

Machine code, I believe. Note that each cell still has one foreground and background, just that both pattern and foreground changes every frame (?) making it look like many colors at once. Usually that kind of flickering would not be preferred but it works great here.

I believe that is correct:  it is a combination of GRAM and color cycling.

 

This is not really that hard, actually, since you can even tell that most of the background cards in the field reuse the same picture on each frame.  You could even do it in IntyBASIC with a DEFINE statement to update graphics, and an ON FRAME routine to cycle through colors.

 

Like @carlsson said, the fast cycling effect and the extensive reuse of a few pictures is typically not desireable, because it flashes too fast and makes it look messy.

 

I think in this case, this effect is only “impressive” insomuch that it looks close to how it did in the original VCS version — but if you think about it, compared to the graphical capabilities of the Intellivision vs. Atari VCS, the original game wasn’t all that impressive visually.  That force-field was just random noise, which was as much as the hardware could take at the time:  a practical and perfectly serviceable solution, but not really one of the best effects done on the VCS.

 

Do not misunderstand me.  The original was and is a great game, even I think so — and I do not like VCS games in general.  This version looks like the original, and since that appears to be its goal, it succeeded.

 

   dZ.

Edited March 22, 2023 by DZ-Jay