Store the time at which a variable reaches a value

[Dan Ebberts]

Exprssions can’t “store” anything. All they can do is set the value of the property hosting the expression. To do what you want to do, your expression will have to look at the property’s value starting at time = 0, frame by frame, until it finds the first frame where the value reaches your target value.

Dan

[Xavier Gomez]

Ok, i’ll put it differently.

The main layer’s position is given by transform.position + Delta-pos(the exact form of the expression Delta-pos is irrelevant here). But,
(1) i want it to be zero until something happens in some other layer
(a quantity, say k, reaches a threshhold value, say k_threshhold);
(2) after that i only know the expression of Delta-pos in local time (time-T) for time>T, where T is the time at which the threshhold was reached. But,… i dont know T ! and i dont know how to tell AE what is the value of T.

[Dan Ebberts]

Like I said, you’ll need to do a frame-by-frame search for the threshold crossing. It will be something like this (not tested):


k_threshold = 10;
P = (whatever property you're monitoring);
trig = false;
for (f = 0; f <= timeToFrames(); f++){
T = framesToTime(f);
if (P.valueAtTime(T) > k_threshold){
trig = true;
break;
}
if (trig){
(do something with T)
}else{
0
}


Dan

[Xavier Gomez]

Thank you, working !

I am still wondering about optimization: this time T either doesnt exist (the threshold is never reached), either is unique (since it is the FIRST time the threshold is reached). So ideally it should be computed only once for the whole composition, and not at each frame.

[Dan Ebberts]

Expressions can’t store any data for use at later frames. So at each frame, it has to again search for a threshold crossing.

Dan