Path: utzoo!utgpu!water!watmath!clyde!att!alberta!myrias!cg
From: cg@myrias.UUCP (Chris Gray)
Newsgroups: comp.sys.amiga
Subject: Re: Ideas for New Custom Chips (a SERIOUS one!)
Summary: modified HAM allows on-the-fly area fills
Keywords: Chips HAM animation
Message-ID: <613@myrias.UUCP>
Date: 7 Jul 88 17:09:04 GMT
References: <3128@polya.Stanford.EDU> <14146@shemp.CS.UCLA.EDU>
Organization: Myrias Research Corporation
Lines: 42

Here's a suggestion for a very simple new mode in the custom chips. Let me
just summarize the current HAM mode: (hopefully correctly!)

    - each pixel has 6 bits
    - only works in lo-res (320 bits horiz) mode, due to bus bandwidth
    - the low-order 4 bits are interpreted according to the high order 2
      bits as follows:

	hi-2-bits	    lo-4-bits
	   00		select one of lower 16 colour table registers
	   01		replace R component of colour of previous pixel
	   10		   "    G    "
	   11		   "    B    "

I've most likely got the hi-2-bits values mixed up, but you get the idea.
What I would like to see is a HAM mode that would work with 2, 3, 4, and 5
bit deep displays as follows: (example for 5 bits/pixel)

        5-bits
	 00000	    - use same colour as previous pixel
	 xxxxx	    - select one of lower 32 colour table registers
			(the 0th entry is not accessible, but is still used
			 as the border colour)

The same pattern holds for other depths - all bits zero means use the same
colour as the horizontally previous pixel.

What could you do with this? Well, consider how quickly you can animate a
line drawing. Change the lines to 5 bits deep (slows it down some), and draw
them in the colour that is desired for the polygon to their right. Voila! We
have an image in full colour! The detail and animation speed is limited only
by how fast the bit planes can be filled to all 0's (use the blitter's clear
mode) and small lines can be drawn on it.

The blitter's area fill mode can be used to fake this (going right-to-left
instead of left-to-right, and only drawing a line in a plane if that bit in
the colour number changes across that polygon border). I'm planning on
trying it out. Has anyone done this? How fast can I make it go?
(I want to use it to do the 3-D maze-walk mode in my Explore system.)
-- 
Chris Gray		Myrias Research, Edmonton	+1 403 428 1616
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