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Differences between Atari 2600 and Atari 7800 sprite colors?

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Hi Eric:

 

Thank you for the explanation...

 

:? I'm confused then. *Any* time I've tried to use that third color in 320B mode while using transparency it never shows up on the real thing. Is there something different you have to do (other than set the Write Mode and the DL header) in order for that third color to come out?

 

Thanks,

Bob

Is he maybe using A mode some for frog/snake. How many colors are in the frog and snake? That would give 7 more colors although any transparency in them is probably limited to 160 res.

 

--Ken

Edited by kenfused

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:? I'm confused then. *Any* time I've tried to use that third color in 320B mode while using transparency it never shows up on the real thing. Is there something different you have to do (other than set the Write Mode and the DL header) in order for that third color to come out?

 

Hi Bob,

 

I haven't tested this, but according to the spec MARIA uses the 2 LSBs to determine whether each 5 bit pixel should be written to line RAM. But since the 320 modes split each 5 bit pixel into two display pixels, transparency is a little less intuitive - particularly with 320B.

320B    WM=1,RM=1,RM0=0
    3 colors from 2 palettes + background & transparent, 2 bits / pixel
D7 D6 D3 D2
0 0 0 0    BG + BG / transparent
0 0 0 1    BG + C1 / transparent
0 1 0 0    BG + C2
0 1 0 1    BG + C3
0 0 1 0    C1 + BG / transparent
0 0 1 1    C1 + C1 / transparent
0 1 1 0    C1 + C2
0 1 1 1    C1 + C3
1 0 0 0    C2 + BG
1 0 0 1    C2 + C1
1 1 0 0    C2 + C2
1 1 0 1    C2 + C3
1 0 1 0    C3 + BG
1 0 1 1    C3 + C1
1 1 1 0    C3 + C2
1 1 1 1    C3 + C3

So with 320B you can only use C1 adjacent to C2 and C3 or it is transparent. However, it's also possible to use the background color as an additional color adjacent to C2 or C3.

 

However, the bigger problem with 320 modes is color artifacts.

Edited by EricBall
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Is he maybe using A mode some for frog/snake. How many colors are in the frog and snake? That would give 7 more colors although any transparency in them is probably limited to 160 res.

 

Transparency is always 160 res. MARIA only has two buffers of 160 x 5 bits of RAM to work with. (One buffer is updated by the display list while the other is being displayed.) The 320 modes are just a trick of the output stage.

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I've also been trying to wrap my head around how he got the 3rd color with transparency in 320B mode (so I can apply it to my Pac-Man 320 games - or other games in the future), but I just can't get it.

 

Bob,

please take a look at One on One Basketball.

 

Thank you.

 

 

http://atariage.com/forums/topic/85709-320c320d-may-actually-have-uses/?p=1280025

 

 

 

 

d7ob.png

 

 

 

 

 

 

pwyp.png

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http://atariage.com/...uses/?p=1280025

 

"The 320C mode can be used to combine a two-color 320-dot background with four-color-plus-transparent shapes using two color sets. The foreground shapes will require double DMA bandwidth; because of some annoying quirks in transparency logic, it's possible to make half of a double-pixel be the background color and have the whole double-pixel be opaque, but making the whole double-pixel the background color will make it transparent.

The 320B mode is reasonably nice when using Kangaroo mode, but works very poorly in non-Kangaroo mode."

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The use of 320b mode in froggie isn't very special.

It is realy just mode 320b using character set for 'background' (turtle, cars, logs) and single 'sprite' for frog and snake.

I used two palletes, one for 'background' gfx and one for 'sprites'.

Every 8 pixel row has a dli for changing colors.

The real limitation of mode 320b was nailed by Eckhard in the thread mentioned before here http://atariage.com/forums/topic/68549-320b-help/?p=845100

Let me give kudos for Eckhard, Dan and Eric for their groundbreaking work concerning the 7800 in general here.

Without them (and Bob 'the coding machine' DeCrescenzo of course) the 7800 would be lost into history...

Any questions?

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I made a mistake in the comment above, the DLLI is 16 pixel height not 8.

Here a small snippet of a display list entry:

 

a5: .byte <scrollram+9*scrollbuff+2,$e0,>scrollram+1,$00,$11
.byte <scrollram+9*scrollbuff+1,$e0,>scrollram+1,$1f,$c
frog10: .byte <gfxdata+54,$9c,>gfxdata+6,$40
.byte <gfxdata+$b0,$40,>gfxdata,$9f,$0c
.byte <gfxdata+$b0,$9f,>gfxdata,$90
.byte $00,$00

 

The corresponding display list list entry is .byte $cf,>a5,<a5

 

That's all for a line with cars and the frog.

The two lines after frog10 are just black borders (mode 320d).

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Hi Eric:

 

Thank you for the explanation...

 

:? I'm confused then. *Any* time I've tried to use that third color in 320B mode while using transparency it never shows up on the real thing. Is there something different you have to do (other than set the Write Mode and the DL header) in order for that third color to come out?

 

Thanks,

Bob

 

 

Hi Bob,

 

I haven't tested this, but according to the spec MARIA uses the 2 LSBs to determine whether each 5 bit pixel should be written to line RAM. But since the 320 modes split each 5 bit pixel into two display pixels, transparency is a little less intuitive - particularly with 320B.

320B    WM=1,RM=1,RM0=0
    3 colors from 2 palettes + background & transparent, 2 bits / pixel
D7 D6 D3 D2
0 0 0 0    BG + BG / transparent
0 0 0 1    BG + C1 / transparent
0 1 0 0    BG + C2
0 1 0 1    BG + C3
0 0 1 0    C1 + BG / transparent
0 0 1 1    C1 + C1 / transparent
0 1 1 0    C1 + C2
0 1 1 1    C1 + C3
1 0 0 0    C2 + BG
1 0 0 1    C2 + C1
1 1 0 0    C2 + C2
1 1 0 1    C2 + C3
1 0 1 0    C3 + BG
1 0 1 1    C3 + C1
1 1 1 0    C3 + C2
1 1 1 1    C3 + C3

So with 320B you can only use C1 adjacent to C2 and C3 or it is transparent. However, it's also possible to use the background color as an additional color adjacent to C2 or C3.

 

However, the bigger problem with 320 modes is color artifacts.

 

 

Very interesting. Thank you for the explanation, guys.

 

Therefore, since Ms. Pac-Man 320 already uses both palettes in 320B mode, I wonder if _with Kangaroo mode disabled_ it would be possible (theoretically) have the transparency and use the 320A mode for the ghosts eyes (some images below).

 

Thanks for your kind attention.

 

Marco

 

 

post-29074-0-76822100-1457922572_thumb.png

post-29074-0-87448000-1457922592_thumb.png

post-29074-0-78435000-1457922610_thumb.png

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Very interesting. Thank you for the explanation, guys.

 

Therefore, since Ms. Pac-Man 320 already uses both palettes in 320B mode, I wonder if _with Kangaroo mode disabled_ it would be possible (theoretically) have the transparency and use the 320A mode for the ghosts eyes (some images below).

 

Thanks for your kind attention.

 

Marco

WM RM1 RM0  mode details
 0  0   0   160A 4 color, 2 bits/pixel
 1  0   0   160B
 0  1   1   320A 2 color, 1 bit/pixel
 1  1   0   320B 4 color, 2 bits/pixel
 1  1   1   320C
 0  1   0   320D

You can only change the write mode on the same line, so the only option is 320B -> 320D. Easier option is to simply have more sprites with the different eye positions.

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WM RM1 RM0  mode details
 0  0   0   160A 4 color, 2 bits/pixel
 1  0   0   160B
 0  1   1   320A 2 color, 1 bit/pixel
 1  1   0   320B 4 color, 2 bits/pixel
 1  1   1   320C
 0  1   0   320D

You can only change the write mode on the same line, so the only option is 320B -> 320D. Easier option is to simply have more sprites with the different eye positions.

 

 

Thanks for the reply, Eric. Glad to hear that 320B -> 320D mode is an option for the ghosts eyes.

 

Maybe one day, Bob could take a look. :)

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