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info@yasharozov.com
info@yasharozov.com
Participating Frequently
May 17, 2017
Question

seedRandom - How to get different values every time I preview

  • May 17, 2017
  • 2 replies
  • 7018 views

Hi,
So iv'e used Dan Ebberts script to randomly position a layer across time.
My problem is that every time I preview the comp - my layer traverses the exact same path.
The random numbers generated the first time are regenerated every time I preview the comp. I would like to have a different value for each position every time I preview the comp.

Here is Dan's script:

segMin = .7; //minimum segment duration
segMax = 1.7; //maximum segment duration
minVal = [0.1*thisComp.width, 0.1*thisComp.height];
maxVal = [0.9*thisComp.width, 0.9*thisComp.height];

end = 0;
j = 0;
while ( time >= end){
  j += 1;
  seedRandom(j,true);
  start = end;
  end += random(segMin,segMax);
}
endVal =  random(minVal,maxVal);
seedRandom(j-1,true);
dummy=random(); //this is a throw-away value
startVal =  random(minVal,maxVal);
ease(time,start,end,startVal,endVal)

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2 replies

info@yasharozov.com
info@yasharozov.comAuthor
Participating Frequently
May 18, 2017

Thank You. There is a new problem - The seed seems to be seeding anew every frame so the layer is jumping around rather than the smooth motion I had before...Any thoughts?

Horshack
Horshack
Legend
May 18, 2017

Sorry, I was thinking this was a script rather than expression. My brain is on the fritz this morning

Because it's an expression it has no state outside of each frame it's evaluated for during a playback/render. Which means to get consistent random behavior (smooth motion for your purposes), the expression has to be designed to produce the same random numbers for each invocation, which is how Dan correctly wrote the script. What you're asking is that you want the entire set of random numbers to reset between different renders/playbacks but unfortunately there is no automatic way to do this because the expression has no way to distinguish between being told to draw one frame vs another for a given render/playback vs drawing a frame for a different render/playback.

Although there is no automatic way you can manually cause the expression to use a different set of random numbers by putting a slider control on your layer, adding the control's value to the seedRandom() calculation, and then changing the slider's value manually whenever you want to cause a new random motion path (ie, between renders). Here are the steps:

  1. Add an expression control slider to your layer. (Go to Effects & Presets, type "slider" in search box, then drag "Slider Control" in the search results to your layer
  2. Change the calls to seedRandom() to include the value of the slider control (see code below)
  3. For each new render/preview, manually change the value of the slider to change the random path of your animation

segMin = .3; //minimum segment duration
segMax = .7; //maximum segment duration
minVal = [0.1*thisComp.width, 0.1*thisComp.height];
maxVal = [0.9*thisComp.width, 0.9*thisComp.height];
end = 0;
j = 0;
while ( time >= end){
  j += 1;
  seedRandom(j+effect("Slider Control")("Slider"),true);
  start = end;
  end += random(segMin,segMax);
}
endVal =  random(minVal,maxVal);
seedRandom(j-1+effect("Slider Control")("Slider"),true);
dummy=random(); //this is a throw-away value
startVal =  random(minVal,maxVal);
ease(time,start,end,startVal,endVal)
info@yasharozov.com
info@yasharozov.comAuthor
Participating Frequently
May 18, 2017

Thanks again. I get the logic I think. There is still a problem. Iv'e dragged the slider control effect to the layer and the script doesn't seem to call it. The layer remains stationary and I get an error the likes of "position of layer 1 in comp 'a', effect named 'Slider Control' is missing or does not exist".
I then added a keyframe on the slider control effect and it's script looks like this:
effect("Slider Control")(1) which I guess is the initial value. Still not working...

Horshack
Horshack
Legend
May 18, 2017

You can get a different random value for each preview/render by changing the random seed to use a value that's variant with clock time.

For example:

segMin = .7; //minimum segment duration
segMax = 1.7; //maximum segment duration
minVal = [0.1*thisComp.width, 0.1*thisComp.height];
maxVal = [0.9*thisComp.width, 0.9*thisComp.height];
end = 0;
j = 0;
randSeedBase = Date.now()
while ( time >= end){
  j += 1;
  seedRandom(j+randSeedBase,true);
  start = end;
  end += random(segMin,segMax);
}
endVal =  random(minVal,maxVal);
seedRandom(j-1+randSeedBase,true);
dummy=random(); //this is a throw-away value
startVal =  random(minVal,maxVal);
ease(time,start,end,startVal,endVal)
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