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: Denise/Paula/Agnus/Gary/Portia Summary: Peter/Paul/Mary Keywords: Puff the majik dragon Message-ID: <19145@usc.edu> Date: 12 Aug 89 21:12:50 GMT References: <1388@bnr-fos.UUCP> <1671@cs-spool.calgary.UUCP> Sender: news@usc.edu Reply-To: addison@pollux.usc.edu (Richard Addison) Organization: University of Southern California, Los Angeles, CA Lines: 72 In article <1671@cs-spool.calgary.UUCP> deraadt@enme3.UUCP (Theo Deraadt) writes: >I thought about what would be involved in using a TI 340x0 in an Amiga >system before. The format of the video memory leads me to say it's not >practical. The Amiga is bitplane oriented, as all the graphics.library >structures indicate, while the TI chipsets are pixelpacked. Furthermore, those bitplanes can be scattered around quite a bit unlike the bitplanes of something like the Inconsequential Bit Mover's EGA where the planes are at fairly fixed locations. >Thus, on the Amiga a pixel is formed by grabbing bits from a bunch of >different bitplanes, with the number of bitplanes being completely >variable [up to a maximum that is always too small :-)]. The Custom chips >do one dma cycle for each bitplane then get 16 pixels out of it >[16 is memory bit width]. A 32bit bitplane solution would be able to >display twice as much 16bit bitplane solution. Greater pipelining or >extensive fifo usage could make it even better. Of course, VRAMs would be nice as well since they have the fifos built in. >On the 340x0, it's a little different. If you have one bit/pixel it works >the same. If you have two bits/pixel, then two consecutive bits in memory >generate a pixel. If you have 16 colors, you have 4 consecutive bits >to a pixel. Because the shifting gets icky, you don't get non power-of-two >bits/pixel. Shifting 3 bits at a time out of a 16bit word gets messy >when you get to the end of the word :-) It is easier to build video >shifting circuitry for pixel packing. The bitplane method gives the Amiga much more flexibility in memory consumption. Building video shifting circuitry for bitplane method is not so ugly because of the consistency between working with various numbers of bits per pixel. Video shifting a pixel packed architecture with variable bits per pixel is, on the other hand, rather ugly since it has to unpack in different ways. >There is a National graphics chip set [not sure about availability] that >has a super blitter/display chip for each bitplane, the entire architecture >is 32bit, and has a full graphics processor. I looked at a 10 or so page >pamphlet on it, and it certainly was impressive. THIS THING HAD EVERYTHING, >but it probably takes up a ton of board space.. the main processor had >50ns cycles for some stuff... Could you summarize the pamphlet? >I certainly would much rather stay with a bitplaned approach. Everytime >I think of displaying text on a nonbitplaned multi bit/pixel screen it >scares the heck out of me. Of course these systems do text for you, >but I still think bitplaning is better. Everytime I think about image processing with a bitplane approach I get discouraged. In that case, I'd prefer 8 bits per color component available in one byte. (Yes, and an 8 bit alpha channel, too! How about 12 bits per channel so I can handle overflow? And enough memory for, say, 32 million pixels?) Furthermore, it's a bit easier to do anti-aliased fonts. Of course, you'd want some sort of convolver on it. >I suspect the difficulty in switching to a pixel packed chip such as >the 340x0 using just a new graphics.library is probably prohibitive. >Too much bitplaned data in structures would have to be repeatedly >converted to and from pixel packed format. >>Theo de Raadt (403) 289-5894 Calgary, Alberta, Canada Would the National chip be better suited? Also remember that the graphics library has no restrictions on the relative positions of the various bitplanes. Richard Addison "Time flies like the wind. Fruit flies like bananas."