Parent lens flare centre

[amitzinman]

Hi,
I have a null with some tracking information. I would like to move the lens flare center according to it.
What expression could I use to to parent a property rather than the entire layer?

Amit

[Paul Tuersley]

You should be able to just add an expression to the Lens Flare Center property and drag the expression pickwhip to the null's Position property. Which will give you an expression like:

Code: Select all

thisComp.layer("Null 1").transform.position

[amitzinman]

yes, I did that but it doesn't parent it. Its just follows the null's position which is way far off.

[Paul Tuersley]

There's no built in way to do something exactly like parenting with expressions, but you can put in an offset. Something like:

Code: Select all

thisComp.layer("Null 1").transform.position + [-100, 50];

[amitzinman]

also, not helping if the tracking data has rotation values.

[Paul Tuersley]

I don't really see how rotation comes into it. There's almost certainly a way to do it but maybe you could describe better exactly what's going on, or even better, post a reduced project.

[amitzinman]

Dan Eberts posted this expression as a reply to this query, but in another forum...

L = thisComp.layer("Null 1");
p = L.transform.position;
r = L.transform.rotation;
d = valueAtTime(0) - p.valueAtTime(0);
angle = degreesToRadians(r - r.valueAtTime(0));
s = Math.sin(angle);
c = Math.cos(angle);
x = d[0]*c - d[1]*s;
y = d[0]*s + d[1]*c;

p + [x,y]