Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga Subject: Re: Duped!! Message-ID: <15199@cbmvax.commodore.com> Date: 17 Oct 90 01:32:57 GMT References: <90284.232257JKT100@psuvm.psu.edu> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 38 In article lupe@alanya.Germany.Sun.COM (Lupe Christoph - Sun Germany Consulting - Munich) writes: >To add my two Pfennigs to this: >The good thing is that seemingly most VGA boards do not use the plane >organisation the earlier boards had and the Amiga still has. I.e. the >pixels are not split into single bits with all bit in the same position >of all pixels lumped together, but a chunky organisation, i.e. all bits >of a pixel stored in a single byte. All IBM boards to date, along with Apple, Atari ST, and many other systems use packed pixels rather than bitplanes. Both have their advantages and disadvantages. In general, packed pixels, at least one you have large enough (8 to 32 bit) pixels, is better for on-screen image processing, since you can easily read a pixel value. Bitplane architectures, which, until the Amiga, were mainly found on workstations, have the advantage of being able to draw many graphic objects faster in a CAD or similar environment, since it's not necessary to draw into every plane. They also have the advantage of being more general -- the same routine that scrolls a 4 bitplane display can easily scroll an 8, 24, or 5 bitplane display. Packed pixel displays only make sense in numbers that fit into a machine byte or word easily. Also, bitplane displays are more easily parallelized -- the National Semiconductor RGP85xx chip family, for instance, permits you to build a display with a blitter per bitplane. In such a system, the display speed for many operations is independent of the display depth. >Have you ever seen plane flicker ? That's when the Amiga moves big chunks >of pixels. It has to move them bit plane by bit plane. Sometimes this becomes >visible. And any packed pixel display controller has to scroll pixel by pixel, which can also become annoyingly visible. >| lchristoph@Sun.COM (Internet) | Disclaimer: | -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy Standing on the shoulders of giants leaves me cold -REM