[vos-d] time transforms

[Peter Amstutz]

I just wanted to clear up one misconception I noticed in a few replies 
to my mail.  The key ideas here are:

a) time is relative to the viewer

b) there are many clocks and

c) a clock can be defined in terms of another clock, via a linear 
transform -- this is what I mean by a "time transform".  A clock can 
also specify a modulus base (for looping).


So, for example, an animation loop is specified from time 0 .. 10.  The 
world time is 29, and we started the animation at time 15.

The "world" clock is 29.

The "animation" clock tells us what animation frame to display.  To go 
from the "world" time domain to the "animation" time domain, we need to 
apply a time transform.  This is a linear equation in the form 
 t1 = ((t0 + n) % m) * s

t0 is the world time
s in the time scalar
n is the time offset
m is the time modulus

So in this example, we apply

((29 + (-15)) % 10) * 1
  = (14 % 10) * 1
  = 4

So at "world" time 29 we show animation frame 4.

What's interesting is if you have one animation embedded in another, you 
can define the time base for the second animation in terms of the first 
one.

A couple other points:

 - If a clock is a vobject, then the connections between clocks can be 
parent-child links.  This also means a single clock can drive many 
time-based vobjects.

 - The current assumption is that the root of a virtual space is hosted 
on a single site, so that would also hold the clock for that particular 
space.

[   Peter Amstutz  ][ tetron at interreality.org ][ peter.amstutz at gdit.com ]
[Lead Programmer][Interreality Project][Virtual Reality for the Internet]
[ VOS: Next Generation Internet Communication][ http://interreality.org ]
[ http://interreality.org/~tetron ][ pgpkey:  pgpkeys.mit.edu  18C21DF7 ]

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