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[Xvrml-agents] Re: interpolators
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From: Miriam E. <mi...@we...> - 2005-08-18 23:36:40
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Hi folks, I have to go out shortly, so I'll keep this as quick as I can. Interpolators are neat, but they are one of the hardest things in VRML to understand, also they are NOT general purpose. There are some situations where the scene author knows the startpoint, endpoint, and duration of an action, but in *most* situations only two of these will be known, and sometimes not even that. In such situations the poor author has to go through all manner of contortions to make the awfully over-specialised Interpolator nodes work for them. In many, perhaps most, situations the author will have just a startpoint and a force (and sometimes only a force). I'd suggest leaving Interpolators in for backward compatibility, but spend the time working on coupling any VR display system to a physics simulator like ODE. Let the display just display, and let the physics take care of movements. Interpolators have descended from cartooning, but cartoons and VR are quite different things. You can make VR work like cartoons, and for that Interpolators could be useful I guess, but I think most authors would prefer to be able to throw a ball and have it arc up and down to bounce around without explicitly animating it and without needing to know ahead of time where it will bounce to. It is much more sensible to set one force (the wind) against a tree blowing in the breeze rather than having to animate every darned leaf and branch with Interpolators. I have come to the conclusion that building up general purpose animation libraries (walk, run, jump, etc.) that can be easily adjusted to different characters (a dwarf walks differently from a giant, and a pirate with a wooden leg walks differently from either) is next to impossible using Interpolators. In order to develop such general purpose animation libraries we need to use physics simulators. They exist and are free and open source. We should be using them. Otherwise it is like saying the graphics accelerators in video cards exist, but we'll use the main CPU because that is how it used to be done. Simplify and extend. :) Best wishes, - Miriam David Huffman wrote: >>so >>the first question which came up was >>what exactly is in the "key" element? >> >> numbers from 0.0 to 1.0 [representing % of the way through an >>animation]? >> numbers representing absolute (Unix) time? >> numbers representing absolute (since the simulation started) time? >> numbers representing relative (since it was triggered) time? >> something else? >> >>Dave Huffman had some good thoughts about this issue >>which he expressed during the Team meeting this week... >> >>Dave: you want to chime in on this discussion please? > > > the key element is exactly what it looks like, and i think it should stay the way as it was in the original vrml specs. an unbounded set of numbers that are always increasing. realize that a position interpolator has nothing to do with time. it is only a calculator converting a float value to a new position. it shouldnt be a percentage because it may not necessarily just go from start to end. If it is based on time, then it would go from beginning to end like you are expecting. If it was based on something else, like another objects position, it may not go from start to end so simply. > > i believe strongly of keeping the key a float, as it has no connections to time directly. most people connect a time sensor to position interpolators, but it is not always that way, so we must keep it generic. also note that interpolators are not triggered, the sensors such as the time sensor is triggered. > > i believe we have two discussions here, one for the type of keys in interpolators, which i believe should remain generic, and a discussion on how time should be represented in time sensors. a position interpolator has nothing to do with time unless a time sensor is connected as input, and at that point it is only converting an input to output. interpolators can not be time dependent. > > dave -- ---------=---------=---------=---------=---------=---------=------ A life! Cool! Where can I download one of those from? ---------=---------=---------=---------=---------=---------=------ http://werple.net.au/~miriam My live Journal page http://www.livejournal.com/users/miriam_e/ |
