Why Amigas never had a chunky mode ?

[Thorham]

Per pixel, but you can access 16 pixels at a time.

Only if you have a 1 bit per pixel mode, obviously. There's also the problem that the Amiga blitter accesses memory at 16 bit boundaries, which means you need to blit 16 bits extra for positioning. A chunky blitter that accesses memory at 8 bit boundaries doesn't need the extra bits when blitting to an 8 bit screen.

Can the color registers be modified fast enough to emulate chunky mode?

Yes, but you can't do full screen 1x1 pixel mode that way.

[vxm]

Maybe if Commodore had not refused the RANGER chipset, the 256 colors would have been available.

[kamelito]

Copper Chunky has been done in demo, sure it's not real chunky but show how versatile the Amiga chipset are.
Kamelito

[smerf]

At some points in the 90s engineers at Amiga inc had planned the future with AGA, Super-AGA...

But certainly some engineers said "we will need a chunky mode": it will be simpler to program, more efficient, etc...

And then at this point some director said "it will cost too much" "bitplanes are enough for a game engine" "they can buy a graphic card" and other oddities

What is the name of this stupid man ?

Alain Thellier

Reason Amiga's never had a chunky mode is because they didn't have a bloated Operating System running them.

[grond]

You don't waste RAM, but you waste computing power and bandwidth when manipulating the display.

Did you really read what I wrote? I wrote: "Only if you have 256 colours, you don't waste precious RAM in a chunky mode."

An 8-colour chunky mode would need e.g. 640x256x1 bytes while an 8-colour planar mode takes only 640x256x3/8 bytes, i.e. in each chunky byte some of the bits would be "don't care" and thus wasted. Hence, a chunky mode would have been a waste of precious RAM unless it would have been a 256-colour chunky mode (there are 16-colour chunky modes in some PC gfx cards where each pixel takes on nibble). 256-colour modes were hardly feasible in 1985. When they eventually were, Commodore were too cheap or lazy or stupid to add them.

[SamuraiCrow]

In the age when all PCs had 4 planes max, the Amiga supported 5 or 6 counting EHB mode.  The AGA chipset was just an incremental kludge on that since the AAA chipset was taking too long.  It was important in the beginning to support odd-numbered bits-per-pixel to get 32 or 8 colors without wasting RAM.  By the time AGA came out, they just came out with a hack without even updating the blitter for fast-page mode much less chunky as well.

[psxphill]

Only if you have a 1 bit per pixel mode, obviously.

You are moving 16 bits of one plane, so after operating on all 8 planes you have moved 16 bytes which corresponds to 16 pixels. Which is the same number you move with chunky pixel mode.

There's also the problem that the Amiga blitter accesses memory at 16 bit boundaries, which means you need to blit 16 bits extra for positioning. A chunky blitter that accesses memory at 8 bit boundaries doesn't need the extra bits when blitting to an 8 bit screen.

That is the only situation where planar does require extra bandwidth. While it's nice to have everything as fast as possible, it would usually only be statistically significant on small blits whose time is mostly taken up by the blitter startup.

The tl;dr reason it was planar was that memory was so expensive when they designed the chipset and by the time memory prices dropped, it was too late to change. It was hard enough to get it out there "let's redesign everything because we can make it 1% faster" would not ever happen.

For the longer version...

https://www.youtube.com/watch?v=RXKcMFoRsN4
https://www.youtube.com/watch?v=DOo1HA66BWw
https://www.youtube.com/watch?v=dRNsKvGwKOM

AA was where chunky pixel should definitely have happened, but that project was mishandled by management (and besides it should have been started in 1989 instead of AAA).

[Thorham]

You are moving 16 bits of one plane, so after operating on all 8 planes you have moved 16 bytes which corresponds to 16 pixels. Which is the same number you move with chunky pixel mode.

16 bits of one plane only equals 16 pixels in 1 bit per pixel mode. If you have more than 1 bit per pixel, you're handling parts of pixels. Part of pixel != pixel :p

That is the only situation where planar does require extra bandwidth.

Which is a very common situation: Blitter based sprites (bobs).

While it's nice to have everything as fast as possible, it would usually only be statistically significant on small blits whose time is mostly taken up by the blitter startup.

It's absolutely NOT insignificant. When you're blitting 16 pixel wide bobs (quite common), you're wasting half the blitter time on the 16 extra bits per bob.

Anyway, assuming AGA chunky, I was wrong, because the blitter would still have to access whole 32bit words in memory to get to the individual bytes. That it would get rid of the need for extra shift bits is irrelevant. Only a faster blitter would make sense.

[trekiej]

1/5 of 16 pixels for 5 bit planes.
What is the limitation of a bit-plane system?
It seems to be a flexible system.
It looks as one could design a chip to move almost any number of bits at a time.

[psxphill]

16 bits of one plane only equals 16 pixels in 1 bit per pixel mode. If you have more than 1 bit per pixel, you're handling parts of pixels. Part of pixel != pixel :p

Every word transferred in 256 colour planar mode is 16 * 1/8's of a pixel, in chunky it's 2 * 8/8's of a pixel. The maths works out the same, the fewer the bitplanes the more planar wins in terms of speed.

It's absolutely NOT insignificant. When you're blitting 16 pixel wide bobs (quite common), you're wasting half the blitter time on the 16 extra bits per bob.

Sure, but the overall time of those small blits is then not the blitter bandwidth but the CPU time driving the blitter. The bandwidth itself becomes more important on larger bobs, when the cpu and planar overhead decreases.

Anyway, assuming AGA chunky, I was wrong, because the blitter would still have to access whole 32bit words in memory to get to the individual bytes. That it would get rid of the need for extra shift bits is irrelevant. Only a faster blitter would make sense.

Yes the blitter could be exactly the same if AA was chunky as you still need to shift by 0/8/16/24 pixels, or you would only be able to move bobs on 4 pixel boundaries.

A 32 bit blitter would have been the only practical way to make it faster and the time and money to do that would be difficult to justify, when everyone was saying AAA was the future. Although I'd have probably left the 2d blitter to work with 16 bits for compatibility and added texture mapping, which coupled with chunky pixels would have it easy to write doom clones for the amiga. The 3do was started around the same time as AA was in development, so the idea of a 3d games machine wasn't particularly exotic.

What is the limitation of a bit-plane system?
It seems to be a flexible system.
It looks as one could design a chip to move almost any number of bits at a time.

Yes you could do 32 bit true colour displays with bitplanes, however it wouldn't be worth it.

The main limitation is manipulating images with a cpu is more complex. In 256 colour chunky pixel mode you can use a single byte write to set one colour. In planar mode you need to read 8 bytes, mask the pixel out of each and or in the individual bits of the pixel and write it back. Once you get to 256 colours it makes far more sense to use chunky pixels. The blitter overhead is also a factor, but nowhere near as much as the cpu.

[trekiej]

The progression seems to be toward chunky anyway.
The C64 and eventually the C65 would benefit from the Planar System.

[kolla]

What prevents darn fast planar modes on on modern FPGA?

[Thorham]

Every word transferred in 256 colour planar mode is 16 * 1/8's of a pixel, in chunky it's 2 * 8/8's of a pixel. The maths works out the same, the fewer the bitplanes the more planar wins in terms of speed.

You said:

Per pixel, but you can access 16 pixels at a time.

And that's only correct when you have a 1 bit per pixel mode.

Sure, but the overall time of those small blits is then not the blitter bandwidth but the CPU time driving the blitter.

Is that an estimate or experience?

Yes you could do 32 bit true colour displays with bitplanes, however it wouldn't be worth it.

Just like those ridiculous 24 bit iffs :lol:

[Thorham]

What prevents darn fast planar modes on on modern FPGA?

What's the use? With fast hardware and lots of memory you just don't need planar. More annoying to program, and no advantages.

[psxphill]

And that's only correct when you have a 1 bit per pixel mode.

Ok rain man. We both know I was talking about one plane of 16 pixels.

Is that an estimate or experience?

Don't take my word for it, get an unexpanded a1200 and test it. Just compare an aligned blit to an unaligned one. That gives you the raw starting numbers, then come up with a reason for moving all of those bobs around as static bobs are rather pointless. Then come back and tell us what you found.

More importantly would fixing that particular issue have stopped the amiga from being killed by pc's and game consoles?

Delaying the launch would just have cost them more money. If AA had been started sooner then chunky 256 colour pixels & 32 bit blitter would have been easier to justify, but even then it would have ultimately made no difference.

2d blitting was no longer important. The mega drive had multiple layers of tiles and large number of sprites, the next generation was 3d.

Commodore would have needed 16 bit sound and video with texture mapping hardware, essentially hombre. Unfortunately they had wasted too much time and money on other projects and there was no time to do it, let alone do it properly and have it backward compatible. Although a half way house of 8 bit chunky pixels with non shaded texture mapping even as late as 1992 may have given them a couple of years breathing space (they could probably have done texture mapping in planar but it wouldn't be worth the complexity).

What prevents darn fast planar modes on on modern FPGA?

Nothing. While more memory bandwidth and faster cpu and blitter will improve the speed of planar, they would also improve the speed of chunky pixels. Obviously for backward compatibility the focus has been on planar. My hope is that the future holds chunky and true colour extensions to AA so all screens can be hardware drag-able. Currently the RTG extensions on FPGA appear to be targeted at separate display subsystems that are more suited to Picasso/CyberGFX etc.

[woof]

>In 256 colour chunky pixel mode you can use a single byte write to set one colour.

Of course the original question was intended for 8 bits
"Why Amigas never had a 8bits chunky mode?"

In fact I have all the time asked myself "why when they did AGA with 256 colors didnt they do it as a chunky mode ?" They (the smart engineers at Amiga) certainly realise that 4/5/6 bitplanes got sense in A1000 era but 8 bitplanes didnt have sense anymore...

Of course modifying the blitter would have been a big task   ... but even without an updated blitter an A1200 with 8bits chunky would have been a good idea for games like doom/quake that used mostly the cpu for drawing at that time

Alain Thellier