Warp wrote:
> Kenneth <kdw### [at] earthlinknet> wrote:
>> "Kenneth" <kdw### [at] earthlinknet> wrote:
>>> "Chris B" <nom### [at] nomailcom> wrote:
>>>> #declare P = seed(1);
>>>> #local I = 0;
>>>> #while (I<frame_number)
>>>> #local ThrowAway = rand(P);
>>>> #declare I = I + 1; // added by Kenneth  ;-)
>>>> #end
>>> That's quite interesting, and it makes great sense--it pulls a nice random value
>>> for each frame. I'll try it!
> 
>> Yes indeed, it works as advertised. Wonderful! Who cares if it wastes some rand
>> values; that's what computers are FOR! :-P
> 
>   Actually it doesn't waste any values. In fact, the end result is very
> similar to the #write/#read solution, but without having to use the temporary
> file.
> 
>   Or it is, if you only want one random value per frame. If you want several
> random values per frame, then you have to "read away" all the random values
> from the RNG stream that have been used in previous frames.
> 
>   If the number of random numbers generated per frame varies from frame
> to frame, then it can become difficult to achieve the desired effect
> without #write/#read.
> 
	One way to work around this issue is to use two random streams: the
first is seeded by a constant and read in the while loop with one
iteration per frame, and the second is seeded from the first:
#declare P = seed(1);
#local I = 0;
#while (I<frame_number)
   #local ThrowAway = rand(P);
   #declare I = I + 1;
#end
#declare P = seed (P)

		Jerome
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