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Trying to parent the Light Source Location to my Null, but it's not working.

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Kristopher Wile
Trying to parent the Light Source Location to my Null, but it's not working.
on May 8, 2012 at 9:20:36 am

So basically, I'm adding artificial lights on top of a set of candles, but the camera is moving. So I tracked the camera movement (really the movement of the fireplace on which the candles are sitting) using Mocha and applied the track to a null object. The lights are created using the LF Glow effect from Knoll Light Factory. However, when I try to parent the adjustment layer on which the lights have been placed to the Null, the light sources don't move with the layer, which now moves with my null.

To solve this, I tried using an expression to parent the light source locations directly to the null's position. That way, they'd move the same distance that the null moves, syncing them with the camera's motion. However, this doesn't seem to be working either. All it does it move the light source location (essentially, my candle light) to the location of my null, which is not where I want it to be.

I'm a bit confused. When I normally parent a layer which is offset to the layer to which it's parented, the offset remains the same, regardless of where the parent layer moves. However, the expression seems to eliminate the offset, which I need so that my lights stay on top of the candles.

Anyone know where I'm going wrong with this? Anyone have an expression that would do the trick?

I've tried both:

thisComp.layer("Null Object VFX 51").transform.position

and

thisComp.layer("Null Object VFX 51").position


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Dan Ebberts
Re: Trying to parent the Light Source Location to my Null, but it's not working.
on May 8, 2012 at 7:34:22 pm

I'm just guessing, and I have not tested this, but maybe you need to offset the lights (assuming they're positioned correctly at the beginning of the comp) by the amount that the null has moved. Something like this:

myNull = thisComp.layer("Null Object VFX 51");
value + myNull.transform.position - myNull.transform.position.valueAtTime(0)


Dan



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Kristopher Wile
Re: Trying to parent the Light Source Location to my Null, but it's not working.
on May 8, 2012 at 7:51:53 pm

Thanks for the help! I inputted what you suggested, but no go. I'm really confused, because in theory, that should work. For some reason, these lights remain in place, regardless of what changes in position are happening to the null, or even to the layer on which they've been applied. I'm really confused about this.


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Dan Ebberts
Re: Trying to parent the Light Source Location to my Null, but it's not working.
on May 8, 2012 at 9:20:00 pm

Making the glow layer an adjustment layer seems to cause the original symptom (light source doesn't move with layer) but the expression I gave you for the light source works for me in that case. I don't know why it's not working for you.

Dan



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Kristopher Wile
Re: Trying to parent the Light Source Location to my Null, but it's not working.
on May 8, 2012 at 9:21:22 pm

I'll give it another shot and see if I can't figure out why it's not behaving as expected. I can provide a screen shot if that would help.


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Kristopher Wile
Re: Trying to parent the Light Source Location to my Null, but it's not working.
on May 8, 2012 at 9:41:44 pm

I managed to get it to work by copying the light effects from the adjustment layer and applying them to a new black solid instead. Then I parented the solid to the null and used the Screen blending mode. That worked out great!


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