Copper color-changing restrictions?

Dan Locke · 29 January 2010, 15:39

What are the restrictions on the copper's ability to switch colors between scanlines? I know that it has to be in a gradient, but I don't know anything else.

chiark · 29 January 2010, 17:01

No restrictions. It doesn't have to be in a gradient, either. And you can switch during a scanline - quite a lot of demos use this for a copper plasma effect...

pmc · 29 January 2010, 17:02

The copper can be used to change colours line to line and also within a line.

Within a line there's a limit on colour changes - if I remember correctly the limit is a change every 8 pixels - this is due to a limit on DMA.

To change line to line, you wait for a line and change a colour, wait for the next line, change a colour, as follows:

Code:

 
$2007,$fffe,color00,$0555
$2107,$fffe,color00,$0fff

To change within a line, wait for a line and just start changing colours:

Code:

 
$2007,$fffe,color00,$0111
color00,$0222,color00,$0333

etc. etc.

Bear in mind that if you do the second example you'll have to change the colours several times before you see the change on screen, either that or change the horizontal wait position - in this case you'd change the $07 in $2007 to something larger, say $35 and then you'll see the colour changes sooner.

Any other questions, just shout.

Thorham · 29 January 2010, 17:24

The copper can be used to change the contents of any of the custom chip registers, and this includes the color registers. The copper therefore isn't limited to changing colors, but can be used to setup whole displays for example. Or control sprites, or program the blitter, or... you get the picture

The speed at which these copper moves happen is eight lowres pixels in the border area (without overscan you can set fifteen 12bit colors per scanline in the border), and eight pixels in the screen area for low color modes (16 colors or less).

As said before, there aren't any restrictions, except for speed.

Leffmann · 29 January 2010, 18:09

Actually if you have nothing more than a lowres 16 color display then you have enough time to change all 16 colors each line. You can do at most 57 move instructions per line under the best circumstances.

korruptor · 29 January 2010, 20:40

Do you mean that you can change all 16 between the end of one line and the start of another, or all 16 during the total length of the scanline?

Edit: Dur, didn't read the post above. 15 in the border.

Leffmann · 29 January 2010, 20:56

Sorry, I meant 16 color changes/move instructions between end of the line and start of the next yes, and I just noticed you can do 17 in fact.

Thorham · 29 January 2010, 20:58

Quote:

Originally Posted by Leffmann

Actually if you have nothing more than a lowres 16 color display then you have enough time to change all 16 colors each line. You can do at most 57 move instructions per line under the best circumstances.

I thought it was 15 moves in the border+320/8 moves during the rest of the scanline=55 moves per scanline? Well, it should be at least 55, any more is a nice bonus.

Edit: You checked, and it's 17 moves during the border?

StingRay · 29 January 2010, 21:16

Quote:

Originally Posted by Thorham

I thought it was 15 moves in the border+320/8 moves during the rest of the scanline=55 moves per scanline? Well, it should be at least 55, any more is a nice bonus.

57 is correct. On AGA machines you can do this in 8 BPL even if you use the correct fetchmode.

Leffmann · 29 January 2010, 21:39

Yep. The blue color changes are the 17th and the 57th respectively here:

Thorham · 29 January 2010, 22:50

WinUae is nice and all, but has anyone checked this with actual hardware?

Leffmann · 29 January 2010, 23:00

I haven't got my Amiga here so I can't test, but I trust WinUAE A500 CE mode to be accurate. I've attached the exe here, do you get the same result?

korruptor · 29 January 2010, 23:02

Quote:

Originally Posted by Leffmann

Sorry, I meant 16 color changes/move instructions between end of the line and start of the next yes, and I just noticed you can do 17 in fact.

Ah, brilliant, didn't realise you could do so many. Is that due to lack of bitplane fetching?

Leffmann · 29 January 2010, 23:23

Yeah, if you add more bitplanes or disk, sprite or audio DMA then they will start stealing too many cycles from the copper. But let's hear from someone with a real Amiga hooked up first

Thorham · 30 January 2010, 00:15

Quote:

Originally Posted by Leffmann

I haven't got my Amiga here so I can't test, but I trust WinUAE A500 CE mode to be accurate. I've attached the exe here, do you get the same result?

Sorry, but I can't test it right now, because my A1200 is dead again

Asm1 has offered me a nice deal on an A1200 motherboard, but he still has to check it, and it has to be shipped from the United Kingdom to the Netherlands, so that will take a while.

Off topic: I really wish some company would just buy all the cool old chip sets from Nes to Aga and make the ultimate retro machine. With all those emulators out there, there's probably a big market for a simple box that allows running software from old console and computer platforms.

Photon · 30 January 2010, 00:16

Quote:

Originally Posted by Thorham

WinUae is nice and all, but has anyone checked this with actual hardware?

OCS 512k:
Yes, I have. Don't have time to dig up my "little experiments", I'm gonna let Leffman supply the hard data in the meantime...

From memory,

Basically the copper, just like the CPU, can move a word in 4px clocks. Since the copper needs 2 words to change a color (registernumber, value), it can go no faster than 8px per color change.

As you add bitplanes (why ruin the beautiful chunky pixel display... with stuff covering it??) bitplane DMA will steal cycles from the CPU (but not the copper) until you have 5 or 6 bitplanes on, then copper can change color every 12px and 16px resp, while the CPU is in trouble (and will concede priority to the copper ofc).

So the CPU will be twice as fast in the hblanking, if you want to change palettes each scanline, so 32 colors are certainly possible with only a little overscan, you can increase overscan a smidgeon if you turn off sprite,disk,audio dma.

So. Put simply, both copper and bitplane dma will compete with the CPU's ability to do palette changes, so don't use them "in overlapping raster time". On AGA it should be the same, only the pixelclock is twice as fast.

Rebel-CD32 · 30 January 2010, 01:06

Sorry this isn't going to help answer any technical questions, but if you'd like to play around with the Copper's ability to change colours all over the screen, give CopColEd a try. It lets you make gradients as well as full screen images with the Copper.

http://aminet.net/package/dev/moni/CopColEdV12

I quickly made this with it http://i50.tinypic.com/29w94ck.jpg

pmc · 30 January 2010, 14:55

@ Photon - I'm sure I read somewhere that the copper gradient you used in Blitter Sweet used a trick that allows selection from a larger than 4096 colour palette. Is that correct? If so, care to give us an insight into how that's done?

hitchhikr · 30 January 2010, 21:34

Quote:

@ Photon - I'm sure I read somewhere that the copper gradient you used in Blitter Sweet used a trick that allows selection from a larger than 4096 colour palette. Is that correct? If so, care to give us an insight into how that's done?

Probably switched colors (like displaying $111 in first frame and $222 in second one would give something like flickering $1.51.51.5, etc).

pmc · 30 January 2010, 21:38

Ah OK, that makes sense - thanks hitchhikr.

So maybe have two identical copper lists (obviously except for the colour changes...) and flip them sequentially?

Wouldn't that lead to some kind of flicker though? A bit like what happens when colours are interlaced on the C64 in some graphics modes?

29 January 2010, 15:39	#1
Dan Locke Registered User Join Date: Oct 2009 Location: USA Posts: 111	Copper color-changing restrictions? What are the restrictions on the copper's ability to switch colors between scanlines? I know that it has to be in a gradient, but I don't know anything else.

29 January 2010, 17:02	#3
pmc gone Join Date: Apr 2007 Location: completely gone Posts: 1,596	The copper can be used to change colours line to line and also within a line. Within a line there's a limit on colour changes - if I remember correctly the limit is a change every 8 pixels - this is due to a limit on DMA. To change line to line, you wait for a line and change a colour, wait for the next line, change a colour, as follows: Code: $2007,$fffe,color00,$0555 $2107,$fffe,color00,$0fff To change within a line, wait for a line and just start changing colours: Code: $2007,$fffe,color00,$0111 color00,$0222,color00,$0333 etc. etc. Bear in mind that if you do the second example you'll have to change the colours several times before you see the change on screen, either that or change the horizontal wait position - in this case you'd change the $07 in $2007 to something larger, say $35 and then you'll see the colour changes sooner. Any other questions, just shout. Last edited by pmc; 29 January 2010 at 20:20. Reason: Typos...

29 January 2010, 21:39	#10
Leffmann Join Date: Jul 2008 Location: Sweden Posts: 2,269	Yep. The blue color changes are the 17th and the 57th respectively here: Attached Thumbnails

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29 January 2010, 17:01	#2
chiark Needs a life Join Date: Jan 2008 Location: England Posts: 1,707	No restrictions. It doesn't have to be in a gradient, either. And you can switch during a scanline - quite a lot of demos use this for a copper plasma effect...

29 January 2010, 17:24	#4
Thorham Computer Nerd Join Date: Sep 2007 Location: Rotterdam/Netherlands Age: 48 Posts: 3,833	The copper can be used to change the contents of any of the custom chip registers, and this includes the color registers. The copper therefore isn't limited to changing colors, but can be used to setup whole displays for example. Or control sprites, or program the blitter, or... you get the picture The speed at which these copper moves happen is eight lowres pixels in the border area (without overscan you can set fifteen 12bit colors per scanline in the border), and eight pixels in the screen area for low color modes (16 colors or less). As said before, there aren't any restrictions, except for speed.

29 January 2010, 18:09	#5
Leffmann Join Date: Jul 2008 Location: Sweden Posts: 2,269	Actually if you have nothing more than a lowres 16 color display then you have enough time to change all 16 colors each line. You can do at most 57 move instructions per line under the best circumstances.

29 January 2010, 20:40	#6
korruptor TDI Join Date: Feb 2007 Location: Blitter Town Posts: 124	Do you mean that you can change all 16 between the end of one line and the start of another, or all 16 during the total length of the scanline? Edit: Dur, didn't read the post above. 15 in the border.

29 January 2010, 20:56	#7
Leffmann Join Date: Jul 2008 Location: Sweden Posts: 2,269	Sorry, I meant 16 color changes/move instructions between end of the line and start of the next yes, and I just noticed you can do 17 in fact.

29 January 2010, 22:50	#11
Thorham Computer Nerd Join Date: Sep 2007 Location: Rotterdam/Netherlands Age: 48 Posts: 3,833	WinUae is nice and all, but has anyone checked this with actual hardware?

29 January 2010, 23:23	#14
Leffmann Join Date: Jul 2008 Location: Sweden Posts: 2,269	Yeah, if you add more bitplanes or disk, sprite or audio DMA then they will start stealing too many cycles from the copper. But let's hear from someone with a real Amiga hooked up first

30 January 2010, 01:06	#17
Rebel-CD32 Amiga will never die! Join Date: Nov 2004 Location: Tasmania, Australia Age: 43 Posts: 532	Sorry this isn't going to help answer any technical questions, but if you'd like to play around with the Copper's ability to change colours all over the screen, give CopColEd a try. It lets you make gradients as well as full screen images with the Copper. http://aminet.net/package/dev/moni/CopColEdV12 I quickly made this with it http://i50.tinypic.com/29w94ck.jpg

30 January 2010, 14:55	#18
pmc gone Join Date: Apr 2007 Location: completely gone Posts: 1,596	@ Photon - I'm sure I read somewhere that the copper gradient you used in Blitter Sweet used a trick that allows selection from a larger than 4096 colour palette. Is that correct? If so, care to give us an insight into how that's done?

30 January 2010, 21:38	#20
pmc gone Join Date: Apr 2007 Location: completely gone Posts: 1,596	Ah OK, that makes sense - thanks hitchhikr. So maybe have two identical copper lists (obviously except for the colour changes...) and flip them sequentially? Wouldn't that lead to some kind of flicker though? A bit like what happens when colours are interlaced on the C64 in some graphics modes?

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