Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!rutgers!usc!pollux.usc.edu!addison
From: addison@pollux.usc.edu (Richard Addison)
Newsgroups: comp.sys.amiga.tech
Subject: Re: The Future of HAM
Summary: While we're at it...
Keywords: Overlay bit
Message-ID: <19144@usc.edu>
Date: 12 Aug 89 20:49:05 GMT
References: <1579@psueea.UUCP>
Sender: news@usc.edu
Reply-To: addison@pollux.usc.edu (Richard Addison)
Organization: University of Southern California, Los Angeles, CA
Lines: 43

In article <1579@psueea.UUCP> bartonr@jove.cs.pdx.edu (Robert Barton) writes:
>
> jmdavis@cbnewsd.ATT.COM (j.michael.davis) writes:
>>  At 8 bits per pixel, a HAM mode will be able to DISPLAY 256K COLORS AT ONCE,
>> with a base register table of 64 colors.  (I know there are 256K pixels on a
>> 512x512 screen, but you get the idea.)
>
>  With 8 bits per pixel you would also need 18-bit color registers.  This won't
>work with the current 16 bit register size.  A 7-plane mode would work if you
>had 5-bit video DAC's.  In other words:
>
>planes     registers     bits/reg     colors
>  n         2^(n-2)       (n-2)*3   2^((n-2)*3)
>  6           16            12          4096
>  7           32            15         32768
>  8           64            18        262144

While we're at it, use 7 planes for HAM so that we have 5 bits per color
component plus one bit for overlay for a total of 16 bits per color register.

And, since it would be nice to have a real alpha channel, how about another
HAM mode with 7 planes, and 4 bits per color component with the following
encoding for the top 3 bits to determine to use of the lower 4 bits:

Mode   Meaning
----   -------
0 0 0  Use color register n
0 0 1  Set Red component to n
0 1 0  Set Green component to n
0 1 1  Set Blue component to n
1 0 0  Set Alpha channel to n
1 0 1  Set Hue to n
1 1 0  Set Saturation to n
1 1 1  Set Value to n

Note that this, too, uses 16 bits per color register (4 red, 4 green, 4 blue,
and 4 alpha).  Of course, these 4 alpha bits could be available in other
video modes.

Imagine the nice antialiased genlocking we could do with this!

Richard Addison
"Klein bottles for sale.  Inquire within."