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Old 27 October 2019, 18:16   #1
Jack Burton
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OCS/ECS 16 colors sprites

Hi,

I've a question about (OCS/ECS) sprites.

OCS/ECS allows to link 2 4-colors sprites to form 1 16-colors sprite.
If we join all these 16-colors sprites together we can create a "large" 64 pixel wide sprite.

But, can we freely use all the 15 colors (from 16-31) for this 64 pixels sprite or are there some constraints (like some colors only available to some sprites) ?
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Old 27 October 2019, 18:39   #2
phx
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There are only constraints for 4-colour sprites. All attached 15-colour sprites use the same COLOR17-31 registers.
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Old 28 October 2019, 11:39   #3
Jack Burton
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Quote:
Originally Posted by phx View Post
There are only constraints for 4-colour sprites. All attached 15-colour sprites use the same COLOR17-31 registers.

Thanks for your answer. I thought that even in 16 colors mode some restrictions remained. And BTW 16 colors sprites should be perfectly useable with a 16 colors sliced screen I guess.
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Old 28 October 2019, 12:24   #4
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Yup, they are. It's (IMHO) one of the many ways in which you can see that the Amiga OCS chipset was clearly optimised for using 16 colour/4 bitplane screen modes.

16 colour sprites are also a good match for Dual Playfield modes (for both OCS/ECS and AGA). They can help add a splash of extra colour in those modes.
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Old 28 October 2019, 15:15   #5
DanScott
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If you want to see just what can be done with sprites, then Codetapper's website has some good examples of practical usage:

https://codetapper.com/amiga/sprite-tricks/
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Old 30 October 2019, 20:42   #6
Jack Burton
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Quote:
Originally Posted by roondar View Post
Yup, they are. It's (IMHO) one of the many ways in which you can see that the Amiga OCS chipset was clearly optimised for using 16 colour/4 bitplane screen modes.

16 colour sprites are also a good match for Dual Playfield modes (for both OCS/ECS and AGA). They can help add a splash of extra colour in those modes.
Yes, in fact the Amiga architecture has some interesting features, on a 16 colors screen it's possible to add 15 more colors with sprites and add even more colors with the copper ending with a quite colorful screen if done carefuly, and all of this still being in a 16 colors screen mode !

Regrettably there isn't any OCS/ECS paint program supporting a sliced mode (like Photochrome on the Atari ST), which is strange since the copper should do this pretty easily...

A personal solution consists in using the 256 colors mode (out of a 4096 palette) with Brilliance and then counting the number of colors per lines (blocks of 8 lines in fact) which can be somewhat laborious.

BTW a CLI program which can count colors per line would be an interesting option to check if the number of colors used do not exceed the limit.
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Old 30 October 2019, 20:42   #7
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Quote:
Originally Posted by DanScott View Post
If you want to see just what can be done with sprites, then Codetapper's website has some good examples of practical usage:

https://codetapper.com/amiga/sprite-tricks/

Thanks for the link !
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Old 31 October 2019, 01:55   #8
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Quote:
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If you want to see just what can be done with sprites, then Codetapper's website has some good examples of practical usage:

https://codetapper.com/amiga/sprite-tricks/
I read through a lot of that recently. And I was like "omg I've never even turned on sprite dma, I need to learn!!!"
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Old 31 October 2019, 03:15   #9
Shatterhand
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Probably best usage of hardware sprites ever on an OCS/ECS game:

[ Show youtube player ]
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Old 31 October 2019, 09:48   #10
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Yeah, first off Amiga sprites seem to be shitty, but when you research a bit about them it's nice with the all kinds of stuff you can do with them...

You need to think of them as little helpers instead of being the main actors, like they are on the C64.
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Old 31 October 2019, 09:53   #11
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Quote:
Originally Posted by Jack Burton View Post
Yes, in fact the Amiga architecture has some interesting features, on a 16 colors screen it's possible to add 15 more colors with sprites and add even more colors with the copper ending with a quite colorful screen if done carefuly, and all of this still being in a 16 colors screen mode !

Regrettably there isn't any OCS/ECS paint program supporting a sliced mode (like Photochrome on the Atari ST), which is strange since the copper should do this pretty easily...

A personal solution consists in using the 256 colors mode (out of a 4096 palette) with Brilliance and then counting the number of colors per lines (blocks of 8 lines in fact) which can be somewhat laborious.

BTW a CLI program which can count colors per line would be an interesting option to check if the number of colors used do not exceed the limit.
This so much...
I was thinking lately about how to create a proper Amiga painting program that incorporates Copper color switches.

Not an easy task, though..
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Old 01 November 2019, 09:45   #12
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Quote:
Originally Posted by Steril707 View Post
Yeah, first off Amiga sprites seem to be shitty, but when you research a bit about them it's nice with the all kinds of stuff you can do with them...

You need to think of them as little helpers instead of being the main actors, like they are on the C64.
Impressive (and really noisy)

Probably a little off topic but I am thinking: since games like this one use vertical scrolling and HAM is compatible with both vertical scrolling an sprites, perhaps it could be interesting to try programming something like that with HAM. Obvious drawback is that blitter will have a lot less cycles, that would proably mean less BOBs, smaller and less colorful... But sprites could still be used as if it were a regular 16 colours mode screen

Anyway, I wonder if the result is worth the effort. Gameplay will not be ennanced, I suppose.
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Old 01 November 2019, 10:48   #13
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Gameplay can be brilliant even for 160x100 monochrome graphics

Anyway, what you're describing is essentially a kind of 'Hyper Hybris' (which is a game that uses only sprites for all the enemies on screen). The only trouble would be the player ship/bullets. Might get tricky to do well.
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Old 01 November 2019, 16:11   #14
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Quote:
Originally Posted by Steril707 View Post
Yeah, first off Amiga sprites seem to be shitty, but when you research a bit about them it's nice with the all kinds of stuff you can do with them...

You need to think of them as little helpers instead of being the main actors, like they are on the C64.
Can I say I still think the are kinda shitty?

I know the Amiga was built to use the Blitter as its main source of graphics, but if we had 16 sprites with 16 colors "free" for using per scanline (Or maybe even just 8) it would make such a HUGE difference for gaming development.... even if they were just 16 pixels wide.

Even if you want to use the 8 sprites with 4 colors, their color distribution is kinda silly.
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Old 01 November 2019, 20:19   #15
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Gameplay can be brilliant even for 160x100 monochrome graphics
I recall a Speedy Gonzales game on Game Boy and is perhaps the most enjoyable gameplay to me

Quote:
Originally Posted by roondar View Post
Anyway, what you're describing is essentially a kind of 'Hyper Hybris' (which is a game that uses only sprites for all the enemies on screen). The only trouble would be the player ship/bullets. Might get tricky to do well.
Thank you. I completely forgot that BOBs are almost unusable with HAM. An interesting chore would be to code a routine capable of displaying BOBs on HAM screen (with fringes, of course)

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Can I say I still think the are kinda shitty?

I know the Amiga was built to use the Blitter as its main source of graphics, but if we had 16 sprites with 16 colors "free" for using per scanline (Or maybe even just 8) it would make such a HUGE difference for gaming development.... even if they were just 16 pixels wide.

Even if you want to use the 8 sprites with 4 colors, their color distribution is kinda silly.
Indeed is quite a big limit. Anyway, I wonder how the DMA could have been arranged to allocate more sprites. Perhaps the logic could be sorta the bitplane DMA: the extra 8 sprites could steal some cycles from the CPU.
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Old 01 November 2019, 20:25   #16
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Speaking of DMA. Sprites use the odd cycles. Blitter usually steals even cycles to the 68000.

Does anyone know if Blitter can get odd cycles that are not being used by other devices?

For example, a 320 x 200 lowres 8 colours screen would cause 20 display DMA slots to be unused (odd slots). Could the blitter use those free odd slots?
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Old 02 November 2019, 02:21   #17
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It will ask for every single cycle, odd and even. DMA manager will then decide who gets it based on priority level (and CPU exception rule in regard to blitter).
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Old 02 November 2019, 09:15   #18
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It will ask for every single cycle, odd and even. DMA manager will then decide who gets it based on priority level (and CPU exception rule in regard to blitter).
Good to know. I supposed it but I was not sure. Thank you.
If I recall well, CPU gets one cycle every four if blitter_nasty if not set?
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Old 02 November 2019, 16:08   #19
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If I recall well, CPU gets one cycle every four if blitter_nasty if not set?
Sort of.

If blitter is active and CPU has waited at least 4 cycles (All cycles count, it does not need to be blitter cycle), CPU is guaranteed to get next blitter cycle.
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Old 04 November 2019, 13:08   #20
Jack Burton
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Quote:
Originally Posted by Steril707 View Post
Yeah, first off Amiga sprites seem to be shitty, but when you research a bit about them it's nice with the all kinds of stuff you can do with them...

You need to think of them as little helpers instead of being the main actors, like they are on the C64.


Yes, it's something that seems often misunderstood particularly when you see comments comparing the Amiga with consoles likes Megadrive, PCE, etc. and complaining about the so-called Amiga's weaknesses in term of sprites and gaming capabilities. IMHO the Amiga has a so unusual architecture philosophy that it can't really be compared with other gaming machines.

I understand one can find Amiga's sprites shitty, but as far as I'm concerned, it's a secondary problem. You can have zillions of objects moving on screen, that won't necessarily make a good game if the gameplay is neglected. Better focus on gameplay. My main gaming machine is my MSX2+ and frankly despite having a lower resolution, less colors on screen and sometimes not even scrolling, MSX2 games are far more enjoyable, deeper and have better gameplay than many Amiga games which display a lot more : sprites/BOBs, colors, resolution, parallax, etc. etc.

(I wish I could play Amiga versions of games like Penguin Adventure, Maze of Galious, F1 Spirit, Aleste 2, Vampire Killer, (SD) Snatcher, Undead Line, Ys 1/2/3, etc. which should be technically doable on an OCS Amiga.)

So a good use of hardware sprites on the Amiga, although being rather limited, can add a lot if used properly, like you said they are valuable little helpers.


Well, it was just my 2 cents of course.
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