Conference hydra::amiga_v1

>    It appears they are doing this with the ST version of custom copper
>    lists (critical timing of raster interrupts).  That eats up a bit
>    of the 68000, but then that kind of thing doesn't have the limitations
>    of HAM mode.  Maybe it's time to start doing that kind of thing
>    for the Amiga (at least picture viewers).


If this could be done entirely with the Blitter on the Amiga it would be worth
it.  Otherwise it would so seriously labotomize the Amiga OS you couldn't use
all the nice features we take for granted, not to mention how useless such a
picture format would be since you cant use any Amiga tools on such a picture..

From seeing with Butcher, Digi-view, et all.  The Amiga's graphics mode
with proper dithering could do a respectable enough job without these 
inner muckings..

Robb

(warning - ST fun made here...)

> move.l  #0x8260,RegQ_Rez ; pointer to resolution register
> move.l  #0x8240,qCol0   ; pointer to color register 0
> move.l  #0x8242,qCol1   ; pointer to color register 1
>
> clr.w   0x8240              ; make screen background black


Hmmm, Is that how it's done on an Atari - All those *absolute* references!

    re: .1
    
    The Amiga's copper lists are constantly being played with by the
    OS.  That's how it can do things like pull down screens.  There
    is support for merging a custom copper list in with the OS's lists.
    The Copper should be fast enough to do the palette changes without anybody
    having to resort to 68000 or Blitter mucking about.
    
    The standard Amiga tools had to be taught about HAM, overscan, 
    extra-halfbrite, etc.  The trick is to get a standard format or
    way of doing things.  First you need to have have a reason for
    doing it, like HAM for digitizing pictures.  Spectrum 512 is
    being used for that in the ST world (the one with all the hardcoded
    addresses :-)  ).
    
    Besides, the Apple IIGS supports 256 colors in 320x200 and
    64 colors in 640x200 out of a palette of 4096.  Why must the Amiga
    have max 32 or 4096?  Isn't there room for something in between?
    
    -Dave
    

    There is, using extra halfbright mode.
    
    Express Paint 2.0 uses this to acheive 64 colors.  Only problem
    is, I have a very old Amiga, that doesn't have this feature.
    
    Randy
    

    I'm a bit confused about the Apple's color capabilities.  I think
    the paint programs I've seen for it use 16 colors in 320 x 200 or
    640 x 200 (no 400 line mode; wimps).
    
    However, the Apple press releases claimed that up to 16 colors
    per scanline were allowed.  Is this a software trick that current
    paint programs aren't exploiting?
    
    I agree with Dave; until we either get a 640 x 400 HAM mode (probably
    requires new hardware) a trick is needed to display more colors
    in hi-res.  Even if we could get 256 colors, we could (with overscan)
    produce even higher quality pictures without the restrictions of
    HAM.
    
    Ed.
    

Re: .5

The Apple IIGS does use palette register swapping to increase the number
of colors on the screen by changing the color palette between scan lines.
(It's basically using the trick being discussed.)  Thus it does have the
limitations of the small number of colors available per scan line.  Also,
I believe that the GS cannot completely swap palettes between scan lines.
The scan line for the new palette contains 8 new colors and 8 old colors.

Can someone answer a question for me?  Are the ST paint programs displaying
these 512 color pictures synchronizing reloading the color registers with
the beginning of a new scan line, or are they changing the color registers
as the scan line being drawn.  In the first case, the ST is limited to
displaying 16 (low res) colors per scanline.  In the second case, all
512 colors are available per scan line, but the problem is more complex.
(I suspect that these ST programs are doing this harder case.)

By the way, the Amiga's copper can only load 8 color registers per scan
line reliably (in time for the line to be drawn completely using the
new register values).  All 32 color registers can reliably loaded in
three scan lines time.  If you notice, when you pull down an Intuition
screen, there are three scan lines above the lower screen that are
always drawn in color 0.  These three blank lines are padding inserted
by Intuition to allow it to swap the color palettes between drawing the
different screens.

So, I believe that the Amiga can show an 512 color ST file, but it will
be reduced to displaying it the same way the ST does.  The display program
takes over the entire computer and uses very critically timed 68000
instructions to manipulate the color registers in real time.  At least
a properly written implementation will be able to restore the system
when it exits.

Ugh.  Might be interesting as a novelty, but I don't think it will catch
on.

I take it 

Re: .5


>    I agree with Dave; until we either get a 640 x 400 HAM mode (probably
>    requires new hardware) a trick is needed to display more colors
>    in hi-res.


Don't hold your breath for high res HAM.  It would require 150% of the
total memory bandwidth during video access time.

Maybe on the Amiga 3000?

    I'm pretty sure the ST (Spectrum-512) does the color changes in mid scan
    line.  I saw somebody's attempt at reverse engineering this code,
    and it was a bunch of critically timed MOVs which were executed
    at the beginning of each scan line.
    
    I believe the timing is such that there are some restrictions on
    the arrangement of the colors on a line, but I don't remember.
    
    Steph

    Spectrum is using 3 color palettes, for a total of 48 colors per
    scan line.  Since there is no position info for those color changes,
    I assume that means they divided the scan line into thirds, with
    a separate 16 color palette per section.
    
    I haven't heard of any IIGS programs that do 256 colors, but I haven't
    been reading IIGS magazines.  Just was standing in the local computer
    store reading a book about IIGS graphics.  Apples basically put
    the data structures for the raster interrupts for 256 colors into 
    the OS.  The catch is how much memory lots of colors requires.
    
    One of the fish disks had a demo program, 2 pages in length, that
    played with the copper list.  The header said that during his testing
    he found that he could change the color register every word.
    Note, there is difference between having to update the copper list
    with the screen is being dragged up/down and simply displaying
    a static picture.  Maybe the copper can handle more than 8 for
    that.
    
    Any comments on mixing 320 and 640 scan lines? (80 column text &
    32 colors on the same screen)  Is there a need for that?  I assume
    a custom short screen could do it, but why a screen if you don't
    want to drag it.
    
    -dave
    

Re: .9

>    One of the fish disks had a demo program, 2 pages in length, that
>    played with the copper list.  The header said that during his testing
>    he found that he could change the color register every word.
>    Note, there is difference between having to update the copper list
>    with the screen is being dragged up/down and simply displaying
>    a static picture.  Maybe the copper can handle more than 8 for
>    that.

You may be right about the ability to load more than 8 color registers
per line.  My source of the information was RJ, and I remember that
mumbled something like, the padding scan lines between screen changes
on the display started out at one line, then became two lines, and then
three lines as Intuition slowed down during development.

    Some more details on ST programs that are doing raster interrupts
    to get more colors.  
    
    -dave
    
    =====================================================================
    Newsgroups: comp.sys.atari.st
    Path: decwrl!decvax!mcnc!gatech!udel!rochester!cornell
    !uw-beaver!tektronix!tekig5!wayneck
Subject: Quantum
Posted: 4 Apr 88 22:08:28 GMT
Organization: Tektronix Inc., Beaverton, Or.
 
I just bought Quantum this weekend.  It is a paint program that allows the
user to paint in upto 4096 colors.  I guess the program is okay, it seems to
work but I'm not over impressed by it.  I may just be tainted by Spectrum
which really impressed me. I paid arount $40 for it.
    
   Anyway you get the following:
 
       1. four display modes 
          32 colors - medium res. 4 colors changed 8 times over the picture 
         128 colors - low res. 16 colors changed 8 times over the picture
         512 colors - kind of like Spectrum, gives 32 to 40 colors a scan line
        4096 colors - adds flicking inbetween shades to the 512 mode
 
       2. Lots of drawing tools with a fairly easy to use interface. (easier
          than Spectrum, but not a flexible and fewer tools than Spectrum I
          think). 
 
       3. A set of animation tools that allow one to make flip book style 
          animation.  (I haven't use these)
 
Seems like a lot of bang for the buck?  Well here is what I don't like:
 
       1. Key work copy protection, key word is better than most kinds but I
          think all copy protection is a big pain in the butt for a honest 
          user.
 
       2. Spectrum gives me 48 colors per scan line, I need even more, but
          32 is often too low.  Even thought the manual says "There are some
          limitations to the number of different colors that can occur in a
          small area of screen - but depending on the sort of images are 
          being drawn anywhere from 32-40 colors are available on EACH SCREEN
          LINE - hardly a limitation, really!"  That kind of statment dosen't
          sit well with me, what do they know about what I need.  Spectrum
          gives you upto 15 new colors before the scan line and gives you a
          new color every 10 pixels.  This program only seems to give you a
          new set of 10 colors every 80 pixels.  Not quite the same.  Still
          it is a lot better than nothing.
 
       3. In the 512 and 4096 modes you can only select one color at a time
          to work with.  There is no color selection table and you can't 
          look at the picture while selecting the color.  There are tools for
          setting the color but it real hard for me to compare with only one
          color to work with.  I just don't have a good color memory.
 
       4. You can't draw with the 512 or 4096 colors displayed.  You have
          to draw on a 16 color version instead.  Sometimes colors just go
          away while drawing.  Kind of like using ms to make a nice document.
 
       5. Won't flood fill in 512 and 4096 color modes.  Just rings a bell at
          me.  
 
       6. A warning in the manual stating that you can't use Quantum pictures  
          in your own programs if you want to sell them.  They are putting
          together a Software House Site Licence and Source Code Kit that you
          can buy so that then your program can use Quantum pictures.  I think
          they are nuts!  If I make a picture I can't use it!  Why should I
          pay than anything so that I can use MY pictures. 
 
Anyway I'm not a artist so while I think Spectrum is better, this program 
might be better after some updates and basic changes in attitude.
 
                                      Wayne Knapp

    If the ST pallett only supports 512 colors, how can Quantumpaint
    provide 4096?  Unless they're refering to placing two colors next
    to each other, and the eye blends them into a new color.  DigiView
    ads claim over 100,000 'apparent' colors on screen.
    
    Sounds a little fishy to me.
    

    I think they switch colors on alternate frames--so there are two
    pallette entries per pixel.
    
    Steph
    

    Ah, maybe they try to create an interlaced display; that would explain
    the flickering I've heard of.
    

Re: .13, .14

Their 4096 color mode is a sham.  They really display "Drink Coke!" every
other frame.

			:-)

Re: .4

	By the way, you can have a new chip dropped in so that
	your Amiga will display extra-half-bright mode colors.
	I had it done to my dinasaur about a year ago, I forget
	the cost (under $100)