Path: utzoo!mnetor!uunet!cbmvax!steveb
From: steveb@cbmvax.UUCP (Steve Beats)
Newsgroups: comp.sys.amiga
Subject: Re: rp.Mask and fast graphics
Message-ID: <2984@cbmvax.UUCP>
Date: 21 Dec 87 16:34:10 GMT
References: <1593@ssc-vax.UUCP> <22238@ucbvax.BERKELEY.EDU>
Reply-To: steveb@cbmvax.UUCP (Steve Beats)
Organization: Commodore Technology, West Chester, PA
Lines: 37
Keywords: rp_Mask

In article <22238@ucbvax.BERKELEY.EDU> bryce@hoser.berkeley.edu (Bryce Nesbitt) writes:
>I'd like to see a bitplane minimizer that uses the copper to switch
>some pallete colors so the picture is not affected at all by the dropped
>planes.

I played around with this for a while way back there when we got our first
Amigas.  The first hack I did managed to get all 4096 colors onto a 0, yes
zero, bit-plane display.  You will find that the copper only has a set amount
of discrete positions where the display color can be changed. Using the
following copper instructions:-

	CWAIT row,column
	CMOVE color,color0
	CMOVE color,color0
	CMOVE color,color0
	...

allows you to change color0 once every 4 pixels in lores mode.  This bandwidth
is halved in hi-res mode (actually it stays the same but the pixel bandwidth
doubles) so you can only change the colors every 8 pixels.

I did find a useful place for this though.  You know those annoying fringes in
HAM mode, this technique works really well for getting rid of them.  Basically
you have to scan the line you are interested in and use the CPU to find out
which pixels are furthest from the desired color and replace them with a real
color from the pallette (1-15).  Do this recursively for 14 colors and re-do
the HAM calculations after each pass.  Once you've done this, construct a
copper list that WAITs for the end of the line above and then loads the pallette
with the 14 colors you just calculated.  Repeat for all lines of the display.
The resultant images are really good (I used some demo images from digiview).

Sidenote:  The only real way to store this in an IFF compatible format is to
save the image as 12 bitplane data and re-calculate the copper list each time
the picture is displayed.  Wouldn't it be nice if there was an IFF form to
save the copper list directly (Carolyn). :-)

	Steve Beats