Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!ames!think!husc6!bbn!rochester!pt.cs.cmu.edu!andrew.cmu.edu!mp1u+ From: mp1u+@andrew.cmu.edu (Michael Portuesi) Newsgroups: comp.sys.amiga Subject: Re: graphics chips ideas Message-ID:Date: 22 Aug 88 05:51:29 GMT References: <0Wz-V=Au8k-083IFce@andrew.cmu.edu>, <5490@gryphon.CTS.COM> Organization: Carnegie Mellon Lines: 46 In-Reply-To: <5490@gryphon.CTS.COM> > *Excerpts from ext.nn.comp.sys.amiga: 12-Aug-88 Re: graphics chips ideas J.* > *Dow@gryphon.CTS.COM (1722)* > In article <0Wz-V=Au8k-083IFce@andrew.cmu.edu> bader+@andrew.cmu.edu (Miles > Bader) writes: > >Currently, as I understand it, in instances where you want a > >background to show through (like with sprites, or in dual-playfield > >mode), a particular color register indicates "see-through." > > > >I think a neat way to do it would to be eliminate the special > >behavior of that register, and add another 4 bits to ALL the color > >registers (for a total of 16 bits each), which would be "opaqueness": > >a value of 0 would mean "completely transparent," and a value of 15 > >would mean completely opaque. The color of a pixel would be > >(fg*op)+(bg*(15-op)) for each of red, blue and green, where op is the > >opaqueness, fg is the intensity of this layer, and bg is the > >intensity of the underlying layer. > > > Um, Miles, wanna tell me what the Amiga is going to use for bus bandwidth to > do > all this? Hires 4 bitplanes currently burns ALL the CHIP ram bandwidth durning > the active portions of the frame. The enhancements Miles was suggesting have nothing at all to do with increasing the number of bitplanes and hence bus DMA. What he did suggest was adding a few bits of extra attribute to each color register to describe the "opaqueness" of that color on the screen. The amount of bus bandwidth necessary to fetch these extra bits is nominal. The only thing not nominal is the chip space necessary for an extra four bits on every color register plus the additional logic necessary to compute pixel colors based on opaqueness as the raster is being generated. Besides having the only computer system whose interface would support transparent and translucent windows, you could do some *amazing *video effects by having various levels of transparency implemented in hardware. Since the Amiga's future is going to lie in desktop video production, it doesn't seem such a bad idea. You can simulate this right now in software using HAM mode, but it takes lots of CPU cycles to lay down an image properly. --M Michael Portuesi / Information Technology Center / Carnegie Mellon University ARPA/UUCP: mp1u+@andrew.cmu.edu BITNET: rainwalker@drycas "if you ain't ill it'll fix your car"