Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga
Subject: Re: EXTRA_HALFBRITE (was V1.3 OS?)
Message-ID: <47593@sun.uucp>
Date: 30 Mar 88 19:28:23 GMT
References: <7425@agate.BERKELEY.EDU> <471@hub.ucsb.edu> <44456@sun.uucp> <204@toylnd.UUCP>
Sender: news@sun.uucp
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 30


My original statement :
 So no, it is not feasible to design in support for non-ehb machines. You
 assume they have it. 
 
David Albrecht's reply in <204@toylnd.UUCP> : 
> Disagree.

Followed by a very good case for providing a non-EHB fallback position,
with which I can find no fault and revise my statement above to :

  "If you do use EHB, then design in an alternative for machines that
   don't have it."

On a related note, what most people have failed to mention, is that Extra
Half-Brite mode is essentially worthless as it is implemented. Basically,
the way it works is a 6 bit pixel takes the contents of the color register
addressed by the lower 5 bits, and shifts all of the R,G,B values right by
one bit and uses the resulting color. So if you had white (15,15,15) in
color register 0, then a pixel value of 32 would give you grey (7,7,7)
in the output. Note that both (15,15,15) and (14,14,14) in color registers
give you the same output. About the only thing it does well is give you
a fast shadow effect. Using a 32 color image you can cast 'shadows' by  
putting a mask in the sixth bitplane. Anyone else come up with a use for
it? Note that you can also cast pretty decent shadows by writing a checker-
board pattern of black into the background. 

--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.