From: bm@cs.columbia.edu (Blair MacIntyre) Subject: Re: TECH: Input needed on VR setup, OS, software, graphics cards. Date: 15 Mar 1996 09:38:13 -0500 Message-ID: Organization: Columbia University From: bm@cs.columbia.edu (Blair MacIntyre) >>>>> On Wed, 13 Mar 1996 20:19:55 GMT, js@wolfenet.com (Jay >>>>> W. Summet) said: Jay> I am planing on setting up a small homebrew VR system this Jay> summer, and I'm interested in hearing people's suggestions. Jay> I plan on spending: 2000-3000 dollars (US) Buying some combination of: Jay> One or Two bare bone Pentium computers. Jay> One or Two hardware 3d graphics accelorators. Jay> Currently, I have been looking at Omnicorp's 3dDeamon that uses Jay> the 3dlabs 300sx chip. This card already has built in support for Jay> frame sequential stereoscopic NSTC output, and would work great Jay> with my Vio I-Glasses. First, and most importantly, this should be cleared up. The vIO Iglasses support 3 kinds of stereo: - Frame sequential. The left eye is sent to the glasses, followed by the right, in alternating frames. 120Hz refresh is therefore needed to refresh each eye at 60Hmz. This is what many high-end machines put out, such as Sun's Creator3D or the various IRIS or HP machines. - 2 variations of scanline stereo. The odd scanlines represent one eye, the even another. The Iglasses can send the odd lines to the left or right eye (thus 2 modes). You need hardware support to do the first, since the frames have to be sent out precisely alternating N times/second. The Omnicomp 3DemonVR supports it. However, you can do the latter kind of stereo with any display. You simply render the two eyes interlaced. The Iglasses CD has demos that use this mode. The advantage here is that you don't need hardware support. Renderware, for example, supports this. I assume Direct3D will support it, too, when it is released. In fact, lots of things support this. Jay> However, it costs around 1800$ last time I checked. Yes, it does. Jay> The Creative Labs 3D Blaster uses another version of the 3dLabs Jay> 300sx chip (this one does not support OpenGL as far as I can Jay> tell) and only costs around 300-400$. According to conversations I had with someone from 3DLabs on the comp.graphics.api.opengl newsgroup, the PCI version (if it's based on the PERMEDIA) will support OpenGL. However, the 3D Blaster may instead be based on Rendition's Verite chipset. Regardless, on Windows 95 (and perhaps NT), any board that supports Direct3D will support OpenGL because OpenGL will go through Direct3D (unless a specific driver is available, I suppose). Finally, it's not at all clear that you want to use OpenGL. For VR apps, especially with the low resolution HMDs like the I-glasses, you are probably better off with things like Renderware (or Direct3D). They are designed for this sort of thing. Jay> It looks like I might be better off buying TWO pentium bare bone Jay> computers (500$ or less each) networking them, and puting a 3D Blaster Jay> in each of them, and then buying the VGA to NSTC converters along with Jay> a Frame Sequential multiplexer to interface to my Vio I-Glasses. I would wait until I needed to buy the card to decide. They are coming fast and furious these days, and it's not clear how the new ones will perform. Jay> I would like to know if anybody has any comments on this, Jay> specifically: Jay> 1. I suspect that the 3d Deamon is a much better card, but do I Jay> really need all the nice features it offers? No, I don't think so. The big thing you get from the more expensive cards is support for higher resolutions. For driving stereo hmd's at 640x480, cheaper cards will do. I would figure out what your options are for graphics software and then see what cards support it. Jay> 2. According to the specs, TWO 3d Blasters SHOULD give me a much Jay> better polygon count than ONE 3d Blaster, and would cost about the Jay> same, along with a second computer to spread the geomotry calculations Jay> out a bit. Jay> 3. (2) VGA-NSTC converters and a frame sequential multiplexors should Jay> not cost more than 300-400 dollars, RIGHT? I seriously doubt that. I suspect frame sequential multiplexors to be reasonably expensive. I wouldn't waste my time with that solution. Furthermore, I would consider software solutions, like Renderware. You may be better off getting one dual-processor pentium than two single processor ones, and writing your code using lots of threads to spread it out, and effectively devoting one processor to graphics. Jay> 4. Will networking the two computers make the software a LOT harder to Jay> write? (I am also considering using a third computer (486) as the main Jay> controller, and just using the Pentium's for graphcis rendering.) Writing a networked VR system is non-trivial (ask me, I've been working on one for a year now). Unless you have a REALLY REALLY compelling reason, I wouldn't consider that route. You will also introduce lag because the tracker data from the vIO (which is pretty slow to start with) will now have to go over the network. And, you'll have to try and synchronize the frame updates. Just say no. Jay> Now, for some software questions: Jay> 1. I would sort of like to use Linux for my system, because: Jay> a) It's free. Jay> b) It has some good freeware C compilers that would work well. Jay> c) It's fully 32bit, multitasking, stable, and has full network Jay> support built in. Linux is ok, except you will severly limit yourself to what you can use for graphics. In fact, for this summer, you will have a choise of one (1, yes 1) graphics card that support accelerated 3D under X (see the Metrolink homepage at www.metrolink.com). Jay> Would Win95/NT/IBM Warp or some other OS be better? Yes. Every 3D card that is coming out will support Windows95 1st and WindowsNT second. I don't know about Warp, but I haven't seen much in the way of support. Jay> 2. I don't really WANT to write all of the code for my system, I would Jay> be more than happy just making the high-level user interface, main Jay> control loop type of stuff. What type of low level object/graphics Jay> libraries exist, and would they have built in support for either the Jay> 3d Deamon (Open GL) or the 3d Blaster? (As well as support for Jay> distributed processing with twin computers?) By this summer, I may release a simple version of my system which will do most of what you want. But I wouldn't count on it, and it doesn't really meet some of your needs: - it's written in modula-3 and obliq, not C - it requires a lot of disk space (~100-200M) On the bright side, it's fully networked, support OpenGL and Renderware on Linux, NT and Windows 95, and allows you to do VR type apps using an extremely cool interpretted, distributed language (Obliq). -- Blair MacIntyre (bm@cs.columbia.edu), Graduate Student (Graphics and UI Lab) smail: Dept. of Computer Science, 450 Computer Science Building, 500 W 120 St. Columbia University, New York, NY 10027