Dedicated CHUNKY MODE on Amiga: How feasible is it?

[Juz400]

Originally Posted by Bruce Abbott

Finally there is the solution that could have been applied to any Amiga 'back in the day' - a card which produces a dedicated 320x200 chunky display whose output is combined with the Amiga's RGB video output. It could be switched in via a transparent color like a genlock does, allowing overly of sprites etc., and even take part in screen dragging. Of course the blitter can't touch it, but you don't need it because you will be doing all rendering via the CPU.

A 320x200 8-bit frame buffer only needs 64kB. 128kB would give you double buffering, and is still a piddling amount of RAM. The controller could easily be implemented in a medium scale CPLD, which would probably be much easier than trying to redesign the AGA chipset to do it. In effect you would be integrating an RTG card which only has one screen mode. Next step after that is hardware texture-mapped 3D - imagine the Amiga with PlayStation graphics!

I have wondered why no one seems to have gone this route, its seems the easiest way of doing it.
The CD32 FMV card does this, it has a 24bit Video DAC running at 40Mhz, the CD32 combines it with the Amiga display using the Genlock.
A `simple` frame buffer somewhere in the Z2/Z3 memory area could have been implemented on any amiga and would have produced almost no compatability
issues with the Amiga chipset. Presumably a bit slow on 68000 based machines but if combined with a 68030 card for full speed memory access, you could
have updated the whole display in a single frame, how would it have compared to an ISA VGA card?

[Foebane]

Originally Posted by Juz400

The CD32 FMV card does this, it has a 24bit Video DAC running at 40Mhz, the CD32 combines it with the Amiga display using the Genlock.

I remember going into my computer shop and seeing a CD32 playing Top Gun (a shower scene if I recall correctly) with the FMV, and later on Star Trek 6, and they both looked good, I thought.

[vulture]

I think the Graffiti did that too and it was inexpensive
https://bigbookofamigahardware.com/b...ct.aspx?id=498

[AmigaHope]

Originally Posted by vulture

I think the Graffiti did that too and it was inexpensive
https://bigbookofamigahardware.com/b...ct.aspx?id=498

No, the Graffiti was one of a type of external devices that read 4-bit digital RGBI output from the video port and produced a new analog RGB signal using the data.

Other devices that worked like this were Black Belt Systems' HAM-E, and Digital Creations' DCTV.

Basically you'd open a normal Amiga 4-bit hires screenmode, with a magic cookie at the beginning of the data that would tell the device that it was expected to convert the video. It would then read off the RGBI pins and munge the data into its own DAC to create an 8-bit lores display. The HAM-E took it a step further by implementing its own form of HAM8 -- even before AGA existed. The DCTV used the data to produce a luma/chroma waveform instead of RGB.

These devices were relatively cheap because they didn't need a framebuffer (and thus didn't need RAM), instead they just took existing data from the Amiga's framebuffer and used it to produce a new signal that the Amiga couldn't produce.

Graffiti was special because it had a small buffer that could interpret semi-chunky data written to bitplanes, lowering the number of operations needed to display chunky data. (You couldn't write all the chunky data to a plane, but you could alternate planes that you wrote chunky pixels to and the Graffiti would reassemble them in order in its buffer. I don't remember how big the buffer was but it was probably either an 8-pixel buffer or a line buffer)

[chb]

Originally Posted by AmigaHope

Graffiti was special because it had a small buffer that could interpret semi-chunky data written to bitplanes, lowering the number of operations needed to display chunky data. (You couldn't write all the chunky data to a plane, but you could alternate planes that you wrote chunky pixels to and the Graffiti would reassemble them in order in its buffer. I don't remember how big the buffer was but it was probably either an 8-pixel buffer or a line buffer)

AFAIK it was an 8 pixel buffer for c2p-conversion. The data sent from the Amiga was always chunky (so 1 pixel = 1 byte in memory), but depending on the screen mode the pixel order was not linear but scrambled - e.g. pixel 1 went to plane 1, pixel 2 to plane 2, then pixel 3 again to plane 1 etc.

The kind of scrambling was dependent on the screen mode; shires in one plane would give you a linear framebuffer with half of lowres resolution (160*256), two planes were needed for normal lowres, four planes for hires. If normal hires was used as the Amiga screenmode, number of planes had to be doubled accordingly (but 4 was maximum due to digital RGBI).

The Graffiti works with all chipsets, but as OCS does not support shires, you need 2 plane hires and a scrambled buffer for 160x256, while on ECS and AGA it can be linear.

BTW: The Grafitti was activated by setting the genlock audio pin; I remember one program (a demo, of course) that enabled it needlessly and thus showed only garbage when the Graffiti was connected. IIRC, you could also mix planar and Graffiti screens by toggling the genlock audio bit mid-frame. Nice clever little device, but it did not see much use unfortunately.

[Silverstreak]

I always thought there was some milage in using a shires mode, so 1280x256 in HAM6. Looks like this person beat me too it! (haha). Quite an interesting approach though.

https://amycoders.org/opt/fasttruec2p.html

[AmigaHope]

Originally Posted by chb

AFAIK it was an 8 pixel buffer for c2p-conversion. The data sent from the Amiga was always chunky (so 1 pixel = 1 byte in memory), but depending on the screen mode the pixel order was not linear but scrambled - e.g. pixel 1 went to plane 1, pixel 2 to plane 2, then pixel 3 again to plane 1 etc.

The kind of scrambling was dependent on the screen mode; shires in one plane would give you a linear framebuffer with half of lowres resolution (160*256), two planes were needed for normal lowres, four planes for hires. If normal hires was used as the Amiga screenmode, number of planes had to be doubled accordingly (but 4 was maximum due to digital RGBI).

The Graffiti works with all chipsets, but as OCS does not support shires, you need 2 plane hires and a scrambled buffer for 160x256, while on ECS and AGA it can be linear.

BTW: The Grafitti was activated by setting the genlock audio pin; I remember one program (a demo, of course) that enabled it needlessly and thus showed only garbage when the Graffiti was connected. IIRC, you could also mix planar and Graffiti screens by toggling the genlock audio bit mid-frame. Nice clever little device, but it did not see much use unfortunately.

Definitely a neat trick! The marginal speed gain on all but the most simple rendering engines also helps demonstrate that the real enemy was chip RAM speed, not c2p. =/

[eXeler0]

No one mentioned VIDEL yet? Falcon was out by 92 so Atari must have realized that Chunky mode would be good to have a couple of years before that. Not sure their design was the most elegant though..

[Toni Galvez]

Originally Posted by chb

AFAIK it was an 8 pixel buffer for c2p-conversion. The data sent from the Amiga was always chunky (so 1 pixel = 1 byte in memory), but depending on the screen mode the pixel order was not linear but scrambled - e.g. pixel 1 went to plane 1, pixel 2 to plane 2, then pixel 3 again to plane 1 etc.

The kind of scrambling was dependent on the screen mode; shires in one plane would give you a linear framebuffer with half of lowres resolution (160*256), two planes were needed for normal lowres, four planes for hires. If normal hires was used as the Amiga screenmode, number of planes had to be doubled accordingly (but 4 was maximum due to digital RGBI).

The Graffiti works with all chipsets, but as OCS does not support shires, you need 2 plane hires and a scrambled buffer for 160x256, while on ECS and AGA it can be linear.

BTW: The Grafitti was activated by setting the genlock audio pin; I remember one program (a demo, of course) that enabled it needlessly and thus showed only garbage when the Graffiti was connected. IIRC, you could also mix planar and Graffiti screens by toggling the genlock audio bit mid-frame. Nice clever little device, but it did not see much use unfortunately.

Commodore could have add a Grafitty in any Amiga 1200/4000 at that time, Doom could have been true for 030 machines with Grafitti.

[eXeler0]

Originally Posted by Toni Galvez

Commodore could have add a Grafitty in any Amiga 1200/4000 at that time, Doom could have been true for 030 machines with Grafitti.

Well the Indivision ECS has grafitti built in doesn't it?
Nemac IV is one of those rare games that support it, and yea ok, it runs on a 030. Not great but back then we would have gladly accepted it.. Probably ;-)