Bruno Cabasson wrote:
> andrel <a_l### [at] hotmailcom> wrote:
>> Bruno Cabasson wrote:
>>> Concerning the animation problem, I see things as follows:
>>>
>>> Solution 1:
>>> -----------
>>> The nth frame I(n) of an animation is a function of time only. Its
>>> description depends on the sole time parameter. Then you can conceptually
>>> write:
>>>
>>> I(n) = F(tn), with F being the function that describes the scene at time tn.
>>>
>>> This is POV's point of view, through the 'clock' variable and reparsing the
>>> whole scene (except radiosity and photon maps if so specified).
>>>
>>> This solution requires only the description of the F(t) function.
>>>
>>> Solution 2:
>>> -----------
>>> The nth frame I(n) is made by delta wrt first frame. Its description relies
>>> on the description of first frame at t0 and a delta function that depends
>>> on the time parameter. Then you can conceptually write:
>>>
>>> I(n) = I(0) + D(tn), with D being the function that describes the variation
>>> of the scene between tn and t0.
>>>
>>> This solution requires the decription of I(0) and the D(t) function.
>>>
>>> Solution 3:
>>> -----------
>>> The nth frame I(n) is made by delta wrt previous frame. Its description
>>> relies on that of the previous frame I(n-1) and a delta function that
>>> depends on the two instants tn and tn-1. Then you can conceptually write:
>>>
>>> I(n) = G(I(n-1)) = I(n) + d(tn, tn-1), with d being the function that
>>> describes the variation of the scene between tn and tn-1.
>>>
>>> This solution requires the description of I(0) and d(t1, t2) function.
>>>
>>>
>>> Each of these solution is a different approach with pros and cons and
>>> implies related features and syntax.
>>>
>>> Concerning POV4, which of these is preferable?
>>>
>> none or all
> 
> What do you mean exactly? I don't get your point ...

simply that if at frame n you want to position and transform an object 
you will be allowed to access the state in frame n-1, so you can 
transform incremental (3). You can also reset the transformation 
variables and start from there (1) or first revert to a known situation 
either because POV4 gets a mechanism to make a snapshot or because 
somebody will write a function (formerly a #macro) to do so.

So all will be possible and none will be preferable. It depends on the 
application which one is more natural and if you use a GUI you won't 
even know.

> 
> POV has currently solution 1. 
no, it reparses the scene for every frame.

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