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 {uunet!mnetor,ubc-vision,watmath,vax135}!alberta!myrias!cg