From: Tim Watson Subject: Yet more on Muds - I think Date: Fri, 09 Aug 1991 23:32:45 GMT Message-ID: <1991Aug09.233245.27384@demon.co.uk> Organization: Gated to News by demon.co.uk fortony@herodotus.cs.uiuc.edu (Felix Sebastian Ortony) writes:- >There's no way to convey the sense of age and brittleness of a piece >of ceramic with a computer -- and to those who say "but there will be!", >I must say I have my doubts. I'm sure computers will not be able to emulate >every adjective I can think of -- not ever. I don't entirely disagree but here are a few thoughts on the subject of how you represent objects in VR. At the moment, as I understand it, objects are either dead weights or special cased. Dead Weights:- Objects with mass and other attributes such as rigidity, fragility and strength. This can determine whether and how such objects fall, deform, smash into a million Phong shaded triangles, or damage what they hit. Special Cased Objects:- Objects with just one function. They can't be used for anything else even if in real life you can use them for all sorts of other things. In other words if you have a table, it will behave like a table only in ways that help you solve a specific problem. (e.g. You may be able to put things on it but you will only be able to take advantage the fact that it has a flat horizontal surface - Useful for playing table football or lovemaking - if that fact will help you solve a specific problem.) The thing is that if you want reality objects will have to behave and be able to be treated in real ways. An Example - TOWELS (I apologise for quoting from Douglas Adams) You can:- Wrap one around you for warmth on the cold moons of Jaglan Beta, Sunbathe on it on the marble beaches of Santraginus Five, Huddle beneath it for protection from the Arcturan Megaganats, Use it to sail a mini-raft down the slow heavy river Moth, Wet it for use in hand to hand combat, Wrap it round your head to avoid the gaze of the Ravenous Bugblatter Beast of Traal And even dry yourself off with it if it still seems clean enough. There are, of course, a large number of objects that could do exactly the same things (e.g. Flannels, sheets, blankets, duvets, anaraks etc.). In fact these objects are all related by virtue of being 'FAIRLY THIN AND FLOPPY'. There are other objects which could be described as fairly thin and floppy but whose physical attributes make them unsuitable to be used exactly like a towel. (e.g. Tissue-paper, normal paper, plastic bags, aluminium foil, ties etc.) My idea here is that objects of similar types even with differing physical attributes should be grouped into generic types so that a 'blind' computer program can 'guess' what it can do potentially with an object of that type. A final example to show the 'ideology' behind my kind of object:- You are driving along in a VR land, in your Ford Cosworth with your VR girlfriend (the name of whom escapes me). Suddenly the fan belt on your car breaks and you stop in the middle of nowhere. Fortunately your girlfriend is wearing her best silk stockings, so you take one knot it to form a loop and use it to replace the fan belt. The point here is that the computer should not know that one of the potential uses of stockings, when knotted, is as replacement fan belts, this would be the normal approach, in an adventure say. Instead the computer should look at a normal fan belt and decide that what its looking for is a fairly strong flexible hoop which by chance is something that you can make by knotting stockings.(Stockings work as a kind of ROPE in this context). You should also be able to use anything thing else that you can make form a strong flexible hoop. This will be essential since if I know your VR girlfriend she will have harangued you for five minutes and stormed off by this time. TIM WATSON