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Trigger keyframed effect with checkbox controller
So, I have a drop shadow effect that animates in and out and I need it to do that several times in a sequence. The composition has many layers, so I’ve linked most of the animated elements to a control layer. My goal was to trigger the animation using a control checkbox.
I tried several things that didn’t work. Then I found this expression but it only partially works and I can’t figure out what’s wrong:
p = thisComp.layer("Controls").effect("Top Shadow")("Checkbox");
if (p.value){
gotit = false;
t = time;
while (t >= 0){
if (! p.valueAtTime(t)){
gotit = true;
break;
}
t -= thisComp.frameDuration;
}
if (gotit) time-t else 0;
}else
0
When I turn the checkbox on, the opacity does begin to fade in. However, instead of fading from 0 to 16% over 20 frames, the opacity slowly rises to 100% over the duration of the entire sequence.
Can anyone help me with this?
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4 Replies
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This might get you started. It will trigger the animation wherever there’s a keyframe on the checkbox:
p = thisComp.layer("Controls").effect("Top Shadow")("Checkbox");
n = 0;
if (p.numKeys > 0){
n = p.nearestKey(time).index;
if (p.key(n).time > time) n--;
}
n > 0 ? time - p.key(n).time : 0;
Dan
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When I apply that expression to the drop shadow effect’s opacity, and set a keyframe for the checkbox, it does trigger the opacity to start to fade in, but I have the same problem: instead of fading in from 0% to 100% over 20 frames, it just slowly rises to 100% over the course of about 3,000 frames. What elements of my composition could be interfering with this expression?
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If your layer already has an opacity animation starting at time 0, change the last line of the expression to this:
t = n > 0 ? time – p.key(n).time : 0;
valueAtTime(t)If it doesn’t, try this:
t = n > 0 ? time – p.key(n).time : 0;
linear(t,0,framesToTime(20),0,100)Dan
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Thanks, Dan! That does cue the keyframe animation when the checkbox is activated.
If I wanted to keyframe the checkbox so that when it’s turned off, the keyframes will reverse, is there a simple line of expression to do this? I tried a few variations of examples I found but they seemed to be more complex and either did nothing or just turned the effect off instantly.
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