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Expression is only "updating" via manual cues, not automatically

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Robert Headrick
Expression is only "updating" via manual cues, not automatically
on Feb 4, 2014 at 11:20:19 pm

Hope the title's not too confusing. I'm not even sure how to phrase my issue to google it, so I'm just going to post.

I have Comp 1, inside of which is PreComp 1, inside of which is PreComp 2. PreComp 2 has Time Remapping turned on, and its value has an expression that references an Expression Controls slider on a null object in Comp 1. (I'm trying to rig a walk cycle animation for the first time, PreComp 2 holds various hand positions, PreComp 1 has a different walk cycle position on each frame, Comp 1 has a Null Object that I'm trying to set up to control everything in the various precomps).

I know the expression is working because when I type in a new value for the slider control, the hand position updates accordingly. However, if I try to keyframe the slider control (for example, to close the hand into a fist as the walk cycle begins), it doesn't continue updating as the keyframes change. Essentially, the expression only seems to be "listening" when I manually key in a new value, it doesn't pay attention to "automatic" changes triggered by keyframes or by other expressions. I'd like it to trigger automatically.

Hopefully that makes sense. Thanks in advance!


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Dan Ebberts
Re: Expression is only "updating" via manual cues, not automatically
on Feb 5, 2014 at 1:20:00 am

It's probably because one or both of your precomps don't start at time zero in the parent comp. If that's the case, you need to adjust your expressions to compensate for the startTime offset. You have to reference the precomp as a layer in the outer comp. It usually looks something like this for a single level of nesting:

C = comp("main comp");
ctrl = C.layer("controls").effect("Point Control")("Point");
L = C.layer(thisComp.name);
ctrl.valueAtTime(time+L.startTime)



Dan



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Robert Headrick
Re: Expression is only "updating" via manual cues, not automatically
on Feb 5, 2014 at 2:40:23 am

I knew if anybody could tell me what was going on, it would be Dan Ebberts. :-) Thank you! I don't have the project in front of me any more tonight but I'll try this out first thing in the morning. Looks like it'll do the trick.


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Robert Headrick
Re: Expression is only "updating" via manual cues, not automatically
on Feb 5, 2014 at 2:47:18 pm

I tried this out a few minutes ago and wasn't successful. I'm probably just misunderstanding something in the organization.

Below are three screenshots. Screenshot 1 shows my main comp and the Time Remap expression that is driving the walk cycle animation. Screenshot 2 shows my Walk Cycle PreComp and the original expression that I was using to drive the hand positions. Screenshot 3 shows my attempt at implementing your expression to offset the start time value.

Both implementations, the original and the altered, produce the same results (i.e. I can manually change the hand position but I can't keyframe it to change over time).

Screenshot 1:


Screenshot 2:


Screenshot 3:


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