-
Make a Layer Grow at each Marker
I’d like to make a layer grow at each marker. Thanks to other posts in this forum, I’ve come as far as the attached expression. However, the layer resets to the default scale at each marker instead of building on the current scale. I thought that grabbing the scale using valueAtTime() and plugging in the time of the marker would provide the solution, but it’s not happening. Any ideas?
var growSpeed = 10;
var growPeriod = 0.1;if (marker.numKeys > 0){
n = marker.nearestKey(time).index;
if (marker.key(n).time > time) {
n--;
}if (n > 0) {
t1 = marker.key(n).time;
t2 = t1 + growPeriod;
startScale = scale.valueAtTime(t1)[0];
temp = linear(time, t1, t2, startScale, (startScale + growSpeed));
[temp,temp];
} else {
// do nothing
value;
}
} -
3 Replies
-
An expression has no way to access results from its own calculations at previous frames. There are various ways to work around this limitation. In your case, I think you just need to change the line that defines startScale to this:
startScale = value[0] + (n-1)*growSpeed;
That will accumulate the result of previous markers. I haven’t tested it, but it should be close.
Dan
-
Thank you! That did indeed solve the issue. And I understand better what is going on. I was hoping that valueAtTime would sample the expression-result value at the marker time, but based on your example, it will always sample the keyframed value, which in this case is just the value. So instead we take the current value and add to it the known grow amount from all the previous markers. Great!
Theoretical addendum: if we were growing by a random amount instead of a fixed amount, would there still be a way to track this?
-
In that case, you’d have to use a loop to recreate the random values for each previous maker and add them up.
Dan
Reply to this Discussion! Login or Sign Up