320B issue (AND why you should use 320D)

[Ecernosoft]

Hello!

I'm making ICT2 using 320B (The foreground sprites) and 320D with artifacting to get 12 colors for the background. Yes, I really am using 320D here.

But when I load up the game on my NTSC atari 7800, it looks wrong. His eyes are missing, and his legs and part of his arm is completley gone. What is going on?

 

I've heard of a 320B bug but what is it? I might just need to deal with it but if I can get around it, I will.

 

Here is what it should look like:

; What am I doing wrong? Sorry no pic on real hardware, is almost 10:00 where I live and it's my bed time. Meant to post this sooner.

I also wanted to point out something... 320D is very useful for artifacting purposes. With one palette having 4 variations, you can get 12 colors, with 3 per line, as long as you are willing to work with NTSC artifacting. It's what I'm going to use for ICT2. It's DMA efficient, easy, and gives you lots of color.

Edited August 31, 2022 by Ecernosoft

[Eagle]

https://sites.google.com/site/atari7800wiki/graphics-modes/320b-d-and-kangaroo-mode

[Ecernosoft]

Just now, Eagle said:

https://sites.google.com/site/atari7800wiki/graphics-modes/320b-d-and-kangaroo-mode

Yes... I heard something about in 320B if color 0 and 1 are next to eachother both dissapear or something like that

[Trebor]

39 minutes ago, Eagle said:

https://sites.google.com/site/atari7800wiki/graphics-modes/320b-d-and-kangaroo-mode

Just a heads-up, that site leverages the old software guide. 

 

Some of the information from that guide has been updated through the years.  A likely better source is 7800 8BitDev site, which hosts the most recent version of the Software Guide.  Quoting the site: Several inaccuracies have been discovered and corrected, and new sections have been added.

 

Section CTRL ($3C) specifically references Kangaroo mode.

[Ecernosoft]

17 hours ago, Trebor said:

Just a heads-up, that site leverages the old software guide. 

 

Some of the information from that guide has been updated through the years.  A likely better source is 7800 8BitDev site, which hosts the most recent version of the Software Guide.  Quoting the site: Several inaccuracies have been discovered and corrected, and new sections have been added.

 

Section CTRL ($3C) specifically references Kangaroo mode.

Yes I know- I read that many times. What I'm confused about is what is causing this horrific picture on the 7800 and how can I avoid it in the code versus using Kangaroo mode.

[Synthpopalooza]

I came across this while playing around with interlacing in 320B and 320D

 

Specifically, anything with bit 0 and bit 1 in the same bitpair doesn't display properly (both pixels are bit 1) unless you turn on Kangaroo mode.  This makes the flicker mode 320B harder to do ... with it turned on, you get roughly 10 colors per character cell at 320B resolution, and another 10 from the second palette.

 

For the 320D experiment I tried earlier, it also required turning on Kangaroo mode, for similar reasons.

[Mord]

On 8/31/2022 at 5:39 PM, Ecernosoft said:

Yes I know- I read that many times. What I'm confused about is what is causing this horrific picture on the 7800 and how can I avoid it in the code versus using Kangaroo mode.

 

 

The thing causing the horrific picture on the 7800 (And accurate emulators, not all emulators catch this) is that inside a pixel pair, Color C1 will only be visible if it's paired with a C2 or C3 pixel.  If it's paired with another C1 or the background color both will be transparent.  This limits how you can use C1 without kangaroo mode (which I believe doesn't actually have transparency?).

 

It'll come down to creative sprite creation, keeping a close eye on the glitch above.  If you can, try to use C1 sparingly and in places where it'll always be paired with C2/C3. It's one of the main reasons why if I ever get back on track with Graze Suit Alpha I'm probably going to redo it as a 160A/B mix to get away from all the 320B restrictions.

 

 

[Ecernosoft]

7 hours ago, Mord said:

 

The thing causing the horrific picture on the 7800 (And accurate emulators, not all emulators catch this) is that inside a pixel pair, Color C1 will only be visible if it's paired with a C2 or C3 pixel.  If it's paired with another C1 or the background color both will be transparent.  This limits how you can use C1 without kangaroo mode (which I believe doesn't actually have transparency?).

 

It'll come down to creative sprite creation, keeping a close eye on the glitch above.  If you can, try to use C1 sparingly and in places where it'll always be paired with C2/C3. It's one of the main reasons why if I ever get back on track with Graze Suit Alpha I'm probably going to redo it as a 160A/B mix to get away from all the 320B restrictions.

 

 

Thanks for the info! I'll rework it to see if I can get rid of the bad picture.

By the way, I might not use 320B for the final sprites. 

ICT and ICT2 are "sudo games". I'll probably never make a real ICT finished product. I'm doing this to have fun.

If anyone wants me to finish ICT, I will. If you want me to make it a complete game, I will! It's just that while I really was happy with it's progress, It's not easy to make levels for it. The way I designed the level generation makes it a pain to code.

 

You know, I might go back to 320C because of this restriction. 320C doesn't have these problems AND has more color.

 

Edit: Thanks for the info.

 

 

Edit 2: Yeah, I'm going to try 320C and see if I can do better with it. (If I do anything at all)

Edited September 3, 2022 by Ecernosoft