Hi Chris!

When I talk about time in an animation, I always mean the clock, not the
frames. Since many POV-Ray users are used to, and prefer using the clock as
the time reference, it is important that the particle system can be 100%
synchronized with the clock. It is also important that the results are
exactly the same, no matter how many frames you use, for example so a test
render and a final render will produce the exactly same result in the end.

You talk about 3 methods of animating the particle system. Method 0 is frame
independent (synchronized with the clock), but slow. Method 1 is quick, but
not synchronized with the clock.

What I would like to discuss here is the last method. This is the most
interesting, I think. (I also noted that you "forgot" to state any
disadvantages for method 2.)

What I'm trying to say is, that although the amount of time that passes is
frame independent, the results are not necessarily frame independent too,
like they should be.

Your particle system calculated the movements etc. of the particles in a
number of cycles, steps, or whatever you want to call it. For method 1 and
2, and maybe 0 too (I don't know), the number of cycles are dependent on the
number of frames. Do we agree so far?

For each cycle some calculations are done, and the particles are moved a
little. If we for a final render triple up the number of frames, there will
be 3 times as many cycles, but we compensate for that by moving the
particles 3 times less per cycle. Do we agree so far?

Your particle system includes collision detection, right? While I do not
know the details of your particle system, I know that usually collision
detection can be imprecise when the particles move by big amounts per cycle.
The particles can "fall through" objects or "miss" each other if they move
too far at a time. However, if the particles move a tiny distance per cycle
only, this will not happen. It is probably safe to say that the preciseness
of the particle behavior are generally dependent on how great distances the
particles move per frame. Do we agree so far?

So the preciseness of the particle behavior is dependent on the number of
cycles, and the number of cycles is dependent on the number of frames. So in
fact, the particle behavior is a little frame dependent, even when we use
clock_delta to compensate for the movements. Do we agree so far?

OK, I don't think I can continue any further before I get some more
information. So I'll ask some more questions...

You say that when using method 1 you can animate moving emitters/etc in
simulation time. Can you also move the emitters/etc when you use method 0,
or are there some restrictions with method 0?

Hmm, guess that's it for now. Oh, and the "Do you agree so far?" is a kind
of debugging, so I can detect exactly where we disagree! ;-)

Greetings,

Rune
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