3D layer invisible if facing away from camera -- doesn't like parenting

[N***@adobeforums.com]

I'm using this simple opacity expression from Adobe Live Docs.

if (toCompVec([0, 0, 1])[2] > 0 ) value else 0

However, if I have two layers (a front and back) and I parent one to the other, this expression breaks down because the child rotation never changes. Same thing if I parent them both to a null and rotate the null.

How can I make it work correctly with a parent layer or null?

[D***@adobeforums.com]

The expression doesn't depend on the rotation value, just the layer's orientation in comp space. Did you perhaps flip one of the layers 180 degrees on one axis?

Dan

[N***@adobeforums.com]

Ah, good catch, Dan. I had the orientation of the "back" of the card set to Y180°. It's working now. How would that original expression be written to take orientation into account?

[D***@adobeforums.com]

You could reverse the behavior of the expression like this for the layer that starts out rotated 180 degrees:

if (toCompVec([0, 0, 1])[2] < 0 ) value else 0

Dan