Trigger Expression at Certain Value and Loop/Cycle

[Matthew Leonard]

Forgot to add one more thing. I’ve been looking over the internet trying to figure out how probability functions, but I cannot figure out how it works or how to make it affect a certain property. If I wanted the probability of it flickering at 100% opacity happening 1/100 times, how would that work? If anyone can, would you mind explaining it? Thank you.

[Dan Ebberts]

In general, to have a probability of 1/100 you could do this:

if (random(100) < 1){
// do stuff
}

or,

if (random() < .01){
// do stuff
}

For your other question, I’m thinking you may have gone down the wrong path. What’s the effect you’re trying to create?

Dan

[Matthew Leonard]

Many thanks for clarifying that. The main effect really is to have a value(opacity in this case) to go from 0 to 100, then to 0 again(gradually, as if I keyframed 3 keyframes over a span of 10 seconds using ease keyframes). When it hits 100, it would flicker between my two set values, and this will happen ONLY when the value is at 100(or between any other values). It will always hit 100 at the same place(starts at 5 seconds, so every 10 seconds since the next 100% keyframe would be on the 15th second), so I’m hoping it’s not too complicated to create just using expressions. It would go from 0 to 100 over a span of 5 seconds, then back to 0 at 10 seconds. The flicker duration would be about 1 or 2 seconds, then it would ease out continuing to 0.

I want to do the above, but with expressions that will loop it. Kind of in a pingpong type manner. I tried doing it with my code and the flickers only triggered at the 100% keyframe, but it only triggered when there was a keyframe there. When those 3 keyframes looped for a second time(using loopOut) and it hit 100% without a second set of those keyframes, it didn’t flicker according to my values set.

[Dan Ebberts]

I’d start with something like this:


minVal = 80;
maxVal = 100;
minFlickerDur = 1;
maxFlickerDur = 2;

t = (time - inPoint)%10;
n = Math.floor((time - inPoint)/10)
if (t < 5){
ease(t,0,5,0,100);
}else{
seedRandom(n,true);
flickerDur = random(minFlickerDur,maxFlickerDur);
if (t < 5+flickerDur){
seedRandom(index,false);
random(minVal,maxVal);
}else{
ease(t,5,10,100,0);
}
}


Dan

[Matthew Leonard]

Thanks Dan, that works fantastically. I understand most of it, but would you mind explaining these for me if you have the time?

“n = Math.floor((time – inPoint)/10)” What exactly is this code doing? I understand that Math.floor kind of rounds in a sense, but what would it be “rounding”?

What part/s would I change if I wanted to change the amount of time(it’s at 10 seconds now, so maybe 5,15, or 30 seconds).

How would I include probability in that code? I’m not sure if you can encase an if statement around a bunch of if/else statements.

Creator of many visual effects since 2010.

[Dan Ebberts]

The expression breaks time-since-the-layer’s-in-point into 10-second segments. The calculation for n determines which segment this is (the first one is 0, the second is 1, etc.). The calculation for t determines how far we are (in seconds) into the current segment. This is what drives the DIY looping.

If you wanted to change the cycle time, you’d change all the 10’s to something else (I think it occurs in 3 places), or better yet, make it a variable (I probably should have done that).

How would you want the probability to work?

Dan

[Matthew Leonard]

Alright, got it. The probability would be something simple like: there’s a 1/100 chance of it flickering, else it doesn’t flicker at all. So each time it hits 100, the probability would run.

Creator of many visual effects since 2010.

[Dan Ebberts]

Here’s a revised version that should only flicker half the time (probability = .5):


minVal = 80;
maxVal = 100;
minFlickerDur = 1;
maxFlickerDur = 2;
cycleTime = 10;
probability = .5;

t = (time - inPoint)%cycleTime;
n = Math.floor((time - inPoint)/cycleTime)
if (t < cycleTime/2){
ease(t,0,cycleTime/2,0,100);
}else{
seedRandom(n,true);
flickerDur = random(minFlickerDur,maxFlickerDur);
if (t < 5+flickerDur && probability < random()){
seedRandom(index,false);
random(minVal,maxVal);
}else{
ease(t,cycleTime/2,cycleTime,100,0);
}
}


Dan

[Dan Ebberts]

Oops–that one doesn’t completely use the new cycleTime variable. This should work better:


minVal = 80;
maxVal = 100;
minFlickerDur = 1;
maxFlickerDur = 2;
cycleTime = 9;
probability = .5;

t = (time - inPoint)%cycleTime;
n = Math.floor((time - inPoint)/cycleTime)
if (t < cycleTime/2){
ease(t,0,cycleTime/2,0,100);
}else{
seedRandom(n,true);
flickerDur = random(minFlickerDur,maxFlickerDur);
if (t < cycleTime/2+flickerDur && probability < random()){
seedRandom(index,false);
random(minVal,maxVal);
}else{
ease(t,cycleTime/2,cycleTime,100,0);
}
}


Dan

[Matthew Leonard]

Dan, you truly are the man. Thanks a ton.

Creator of many visual effects since 2010.