Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.hardware Subject: Re: (Video) Hardware Idiots ? Message-ID: <22304@cbmvax.commodore.com> Date: 10 Jun 91 18:05:43 GMT References: <22006@cbmvax.commodore.com> <1991May30.095308.25743@rulway.LeidenUniv.nl> <1991Jun3.202114.4029@newserve.cc.binghamton.edu> <1991Jun3.225024.13052@marlin.jcu.edu.au> <1991Jun4.210724.1246@newserve.cc.binghamton.edu> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 101 In article mmm@reaper.Chi.IL.US (Michael Marvin Morrison) writes: >In article <1991Jun4.210724.1246@newserve.cc.binghamton.edu> consp03@bingsuns.cc.binghamton.edu (Kriston J. Rehberg) writes: >>In article <1991Jun3.225024.13052@marlin.jcu.edu.au>, >>cpmwc@marlin.jcu.edu.au (Matthew W Crowd) writes: >>|>This built in video hardware is what i feel has left the amiga behind >>|>in the graphics department. With a PC/Clone, you have to make a choice >>|>as to what standard you want and most people go for the best/latest one >>|>which prompts developers to pump out better/faster/prettier more >>|>functional boards. Great thing about standards, there are so many of them. >>That is true, but you leave out that this option does exist for the >>Amiga. You can completely replace the display hardware just like the >>IBMs can. That's what the video slot is for. >Unfortunately I must disagree. It appears that what is available at the video >slot is essentially the 'raw' output of the CUSTOM CHIPS. (and the signals >from the parallel port). Therefore you are locked into the custom chips for >your AmigaDos output. Actually, you are both confused. The video slot is something there is no equivalent of on Mac or IBM systems. It's a standard way to allow Genlocks, scan converters, and other video device access to all kinds of signals from the Amiga's on-board video chips. It has nothing whatsoever to do with what kind of video display devices you can add to the Amiga, or in general how you add a new display device to the Amiga. There are a few clever devices out there that modify the Amiga's native display output to change it around somewhat. HAM-E and Hedley Hires are in this category. They simplify some of today's software details, but other than that, have no need to use the Amiga's native graphics except that it lets them mix their screens with native screens on the same display. Most other devices plug into the Amiga expansion bus, just like PClone graphics devices do. The fact that you have a graphics display on the motherboard has nothing whatsoever to do with what you can add in the expansion bus. Any arbitrary display device can live in the expansion bus, the A2410 TIGA display board is a good example. Just like the IBM PC, there's no graphics support for it, or any other arbitrary device, in the Amiga OS. In fact, the only reason that we're having this discussion is that the Amiga OS comes with a set of graphics primitives that currently work on one display architecture, the built-in Amiga chips. On the PC, there are no standard graphics functions. So every program builds it's own, and if you're lucky, your graphics board and program go together. If not, you might drop back to one of the primitive modes. That works on a PC, but consider that you're only running one program at a time. In any multitaking OS, you need an OS level graphics manager. The Amiga has two now, Graphics/Intuition, which only work with the Amiga chip set, and GfxBase's X port, which is retargetable. If someone wanted to build a reasonably quick hack to support alternate graphics boards using the Amiga graphics primitives, they could. Basically, what you would do here is allocate a Chip RAM buffer which is the width, heigth, and depth of your display buffer. All your rendering functions, blits, etc. will work, because the Amiga OS provided Graphics, Inuition, Workbench, etc. as of 2.0 pretty much know how to run on arbitrarily sized displays. The extra bit is that, every so often, your graphics device driver gets a message to update itself. It wakes up, grabs the display out of Chip RAM, and converts it to the proper format for the graphics board being managed, then that board is updated. Quick and dirty, but not really fast. Strangely enough, this is just how Microsoft Windows works; all rendering is done in RAM using an internal display format, which each graphics board is responsible for rendering in it's own hardware-defined format. Everyone really wants things to work the way they do on the Macintosh, or thereabouts. In this senario, each graphics library function can be a call to the graphics device driver. While this makes a graphics device driver much more complex to write, it also means it's possible for graphics to be accelerated. If you have a TI34010 or 34020 out on your graphics board, it'll intrepret the "draw circle" or "fill area" line faster than the blitter would. It'll also do this initially in its own internal format, which is also a big speedup. In any case, the only question is software. Hardware has nothing to do with it, really. >IMHO, a better design of the Video Port would have put the Chip bus signals on >this port, with a takeover ability such as the processor slot has. Using this >design one could create a video board that emulated the blitter/copper using >a TI graphics chip, or whatever chipset you wanted. First of all, there's no way an alien device could live on the chip bus. Secondly, if you really have the thing emulating all Amiga chip functions functions, there no need for it. Most everything could run on this magic new wonder board without change. That's pretty much the way it's done on the PClone machines. Since there's only a hardware graphics standard, many of the TIGA and other alternate architecture display boards emulate VGA registers in hardware. That's absolutely the wrong way to do it, on either the Amiga or the PClones. It's also pretty easy to do on the PClones with something as simple as VGA, but you're in for a nightmare on any other system. >Overlaying chip ram is no longer possible either with the Gary chip. Meaning >that I guess this was possible in the 1000. The OVR* line was never reliable at overlaying any of Chip space, on any Amiga. Regardless, there wouldn't be any need for this, anyway, you sound confused. -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "This is my mistake. Let me make it good." -R.E.M.