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Marc Rühl
Marc RühlCommunity Member
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Looping images really randomlyI

Feb 8, 2010 5:39 PM

I need a constantly changing background for an animation. I use different drawings of the same background and loop them randomly, to avoid this looping look. Unfortunalety when I use random there are always two frames who show the same image. I try to solve this with valueAtTime but I always get an error-message with this expression.

 

temp0 = random();


temp1 = temp0.valueAtTime(time  - .1);


if (temp0 == temp1)

{ temp2 = temp0 + .1; }


else

{temp2 = temp0}


[temp2]

  • Dan Ebberts
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    Dan Ebberts,
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    Feb 9, 2010 10:09 AM
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    To avoid generating the same number twice in a row, you need to keep track of what's happened in the past. How many different images do you have? This expression assumes 10, but just edit the first line to match your number. This is one of those expressions that has to recalculate what's happened on each previous frame, so it might bog down if your comp is fairly long.

     

    nFrames = 10;
    seedRandom(index,true);
    n = Math.floor(random(nFrames));

    f = timeToFrames();

    for (i = 0; i < f; i++){
      n += 1 +Math.floor(random(nFrames-1));
      n %= nFrames;
    }

    framesToTime(n)

     

     

     

    Dan

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  • Marc Rühl
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    Marc Rühl,
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    Feb 9, 2010 10:42 AM
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    Sorry. my english isn't that good. I guess I articulated it not right.

    I have a comp, with, let's say a length of 10 frames. Every frame shows another picture. Now I want to loop it, but then you see that it repeats.

    To avoid that, I activate time remapping and used random() to show another picture of the comp on every frame, randomly. Unfortunalety often there is the same picture on two frames one after another. I thought it would be a solution to check which number random() picked the frame before and if it's the same frame add 0.1, but my expression always gets an error-message.

    As I said, my english isn't that good, I hope you can understand what I want to achieve, but thank you for your help.

     

    Marc

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  • Dan Ebberts
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    Dan Ebberts,
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    Feb 9, 2010 10:52 AM
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    Your English is fine. Maybe it's me that's not articulating very well. :-)

     

    The expression I posted is a time remapping expression that should do what you want. Did you try it?

     

     

    Dan

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  • Marc Rühl
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    Marc Rühl,
    Community Member
    Feb 9, 2010 11:06 AM
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    Ya, I tried it, but there were several sequent frames which showed the same picture, therefore and cause I didn't understand the expression I guessed I didn't make clear what I want to achieve.

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  • Dan Ebberts
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    Dan Ebberts,
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    Feb 9, 2010 11:22 AM
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    Hmmm.... I don't know why it's not working for you. I just tried it and I don't get any repeated frames as far out as I checked (200+ frames or so).

     

    Dan

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  • Marc Rühl
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    Marc Rühl,
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    Feb 9, 2010 11:34 AM
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    I tested it in a 10-second-comp, with a 10-image-loop-comp. And just at the end of the 10-sec-comp the images repeat, but then they repeat very often.

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  • Dan Ebberts
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    Dan Ebberts,
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    Feb 9, 2010 11:51 AM
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    I just tried it on a 20 second comp (at 29.97 and 25 fps) and I don't get any repeated frames. I guess I'd need to see your project file to figure out why it doesn't work for you.

     

     

    Dan

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  • Marc Rühl
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    Marc Rühl,
    Community Member
    Feb 9, 2010 12:45 PM
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    I changed the fps of the comp from 12 to 25. I don't know why, but now it works. Is there something what could affect this in the expression?

    Anyway, thank you a lot for your help. Now I try to figure out what the expression actually does . But can you tell me why my expression doesn't work?

     

    Again, thank you a lot.

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  • Dan Ebberts
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    Dan Ebberts,
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    Feb 9, 2010 1:12 PM
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    Your original expression doesn't work mainly because an expression can't use valueAtTime() to get a value that it calculated previously. The only way an expression can retrieve a previous result for the property to which it is applied is to recalculate it. You can't even apply valueAtTime() to anything other than a property, which is why you got the error message when you tried to apply it to a variable.

     

    Dan

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  • Marc Rühl
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    Marc Rühl,
    Community Member
    Feb 9, 2010 1:39 PM
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    ah ok. Thank you.

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