Warp <war### [at] tagpovrayorg> wrote:

>
>   If you are getting a regular pattern inside one single frame, it's
> certainly *not* because you did a "seed(frame_number)" at the beginning
> of your scene.
>
>   "seed(frame_number)" is not any more likely to produce regular
> patterns than "seed(0)" (or any other value for that matter) is.
>

I *think* you're correct in that, if there are *multiple* calls of rand() within
a single frame--using a single seed(frame_number)--then a pattern isn't
discernible. (I never actually did any definitive experiments to determine
that, though.) But of course it sounds logical.

However, if only ONE rand() value is called per frame, then a pattern is
definitely there as the animation progresses. So, extrapolating that to
multiple rand() calls per frame, there may (or may not) be patterns in *every*
rand() call--*from frame to frame.* Personally, I just don't know.

But as regards pulling just a single rand() per frame, I have to agree with
GregJohn.  Let me quote myself(!) from the above-mentioned newsgroup
post--about the core problem that prompted the post:

"...I *thought* that by simply throwing some multiplier value 'M'
at seed(M*clock) or seed(M*frame_number)--just one time in my POV scene, to use
for the entire animation--would give me 'obvious' random numbers from frame to
frame. Unfortunately, not so. There are, to my great surprise, clear
*almost*-repeating rand() patterns, no matter what seed values I use. And it
shows up quite quickly in animation--usually over 5 to 10 frames...."

"...It's especially obvious when using
strict integer multiples for M--3,6,9,12, for example. Actually, any multiple
of any integer. So simply using clock or frame_number to change the seed value
from frame to frame presents a problem, as they both count up linearly."

In other words, as frame_number progresses linearly, then seed(frame_number)
will start showing patterns quite quickly *from frame to frame.* Again, only IF
one rand() value is called per frame (or so it seems.)

In reality, these patterns are not *exact* duplicates, of course. Depending on
how (and for what) a single rand() value is used in a scene, any resulting
pattern may not even be visually apparent.

KW

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