Link position of layer / effect to center of rotating object

[Dan Ebberts]

Start with this and see if it gets you close:

L=thisComp.layer(“lamp”);
L.toComp([L.width,L.height]/2)

Dan

[Patrick Grossien]

Dan, you’re the man! It looks spot on (no pun intended 😉 ).
Thank you so much.

Just that I understand how this works:
When I grab the info from the layer, it always refers to it’s actual position on the comp?
Because I would’ve guess that width and height are static values.

[Dan Ebberts]

>…I would’ve guess that width and height are static values.

They are, but [width,height]/2 represents the center of the layer in the layer’s own coordinate space (relative to the layer’s upper left corner). toComp() converts that value to comp coordinates.

Dan

[Patrick Grossien]

Ah ok, that clarifies it! Thank you a ton!

[Harold Durnez]

Dammit, I’m still a little lost here..
Where do these expressions get applied to..?

I believe I’m trying to achieve something similar.
I’m trying to link a (Joystick N Sliders) Control to a shape which has only rotation expression. i.e. a Ball with anchor point way up, pendulum swinging left & right.
I’d like my Null to trace the position of the swinging path created by the Rotation expression of Ball layer.

Thanks guys, hope you can help!
H

Harold JM Durnez
harold@fullhd.co.za
http://www.fullhd.co.za
facebook.com/fullhd.co.za
behance.net/HaroldDurnez
vimeo.com/harolddurnez

[Steve Bentley]

The expressions always go on the attribute you want to alter. So selecting the rotation parameter of the layer and then under the Animation menu selecting “add expression” will place the default expression on that attribute – the default just refers to what the layer is already doing. You can then select the line of code and erase it and type your own or pickwhip to have AE generate the code for you.

But you might have a simpler time of it. What about just making the null a child of the pendulum and moving the null to the end? The null will be moved by the rotation on the pendulum you animate, but the null will move out where the arc is transcribed.