@saimo

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saimo wrote: @ErikBauer Quote: AFAIK Banshee cleverly used this trick to obtain transparency effect for rain and big laser beams Game ran on 8 bit screenmode (256 colors max) with 7 bit fixed palette (128 different colors). The upper 128 colors (activated by the 8th bit) were the lower 128 modified as they would look if seen in trasparency through raindrops or lasers. At this point they just had to draw raindrops and lasers as a 1 bit mask on the 8th layer of the screen to obtain the transparency effect. (I red the article long ago and can't find it back now, so sorry if I lost something during all this time and gave wrong informations, but as I see there are plenty of programmers here that can correct me) Yes, Banshee has those transparency effects. IIRC, on the first level it had 2 layers of fog, so, at least there, the graphics were on 6 bitplanes (64 colors) - but for memory and speed reasons, it's likely that the same holds true for the whole game (after all, 64 colors are a lot for a good pixeller, and Banshee's is an excellent one). I'm doing the same for SkillGrid (except that I do that on more layers).

Unless they used the "Checkboard dithering" trick to simulate different levels of fog density:

The transparency mask is filled with alternate pixels for low fog density and with all pixels for high fog density... but again I can't precisely recall how it was handled

Last edited by ErikBauer on 01-Aug-2018 at 01:03 PM.
Last edited by ErikBauer on 01-Aug-2018 at 01:02 PM.

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God created Paula so that Allister Brimble and Dave Whittaker could do music

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@ErikBauer

Quote:

Quote: Yes, Banshee has those transparency effects. IIRC, on the first level it had 2 layers of fog, so, at least there, the graphics were on 6 bitplanes (64 colors) - but for memory and speed reasons, it's likely that the same holds true for the whole game (after all, 64 colors are a lot for a good pixeller, and Banshee's is an excellent one). I'm doing the same for SkillGrid (except that I do that on more layers). Unless they used the "Checkboard dithering" trick to simulate different levels of fog density: The transparency mask is filled with alternate pixels for low fog density and with all pixels for high fog density... but again I can't precisely recall how it was handled

They did use some dithering, but not to obtain the 2 layers of fog. My memory was partially failing me: I watched a longplay, and the double fog layer was not in the city level, but in the desert one. It can be seen between 30:08 and 30:10 in this video. It's worth noting that they could have had 3 different intensity degrees, but they actually used only 2, probably for speed reasons - my guess is that they did it like this:
1. draw fog on bitplane 6 by blitting a few patterns (more or less randomly, with a frequency going from low to high to low);
2. draw fog on bitplane 7 according to the same logic.
This way, they only used the combinations 01 and 11 (unless by chance the patterns on bitplane 7 were blitted in a place where there was no pattern on bitplane 6, but that doesn't seem to happen in the video), whereas using also the combination 10 would have required blitting an additional time to clear bitplane 6.

I have just downloaded a screenshot for each level and checked the colors, and got confirmation that the graphics, effects aside, are in 64 colors.

Last edited by saimo on 01-Aug-2018 at 01:51 PM.

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RETREAM - retro dreams for Amiga, Commodore 64 and PC

@saimo

Cool! It's always nice to learn something new
Thanx for the analysis :)

_________________
God created Paula so that Allister Brimble and Dave Whittaker could do music

Check my Amiga gameplays (ITA)!

@ErikBauer

Quote:

Cool! It's always nice to learn something new Thanx for the analysis :)

You're welcome

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RETREAM - retro dreams for Amiga, Commodore 64 and PC

@saimo

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Those are additional reasons, but the main reason why buffering is necessary is that the CPU can't sync all the time to Paula, even if it just had to write a single byte each time (unless, again, the CPU does not anything else to do).

No, the CPU couldn't sync in practical circumstances. But there is the audio end interrupt for that and the delay after which a new bufffer can be loaded into the audio registers. For live streams being played it also does double buffering. IIRC it needs two IORequests to represent each buffer. I've programmed both the device and library interface years ago.

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Didn't we conclude already that your 15 bit idea doesn't work?

I thought we concluded that my 16-bt idea can't work and I concluded my 15-bit ideas was plausible?

@Hypex

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Quote: Those are additional reasons, but the main reason why buffering is necessary is that the CPU can't sync all the time to Paula, even if it just had to write a single byte each time (unless, again, the CPU does not anything else to do). No, the CPU couldn't sync in practical circumstances. But there is the audio end interrupt for that and the delay after which a new bufffer can be loaded into the audio registers.

I was talking of the no buffering case, which would require the CPU to stay synchronized constantly.

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Quote: Didn't we conclude already that your 15 bit idea doesn't work? I thought we concluded that my 16-bt idea can't work and I concluded my 15-bit ideas was plausible?

No, I had answered to your 15 bit idea (8 bits in one channel + 8 bits in another to get 9 bits resolution*, plus the 6 bits coming from the volume to get 15 bits).

*Almost, as the value +255 is not possible.

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RETREAM - retro dreams for Amiga, Commodore 64 and PC