In my scenario I have two different sets of artwork, one for a lit room and one where the light is off.
So two different images for each element in my scene. I wanted a checkbox expression control to flip between
100% and 0% opacity on all these different layers and control the “light” going on and off.
Connecting the opacity property didn’t cause trouble, I find that the checkbox returns
either “1” or “0” which makes sense.
The “Checkbox” has been renamed “Lightswitch” and is on a .layer in thisComp called “Null 2”
at the end multiplies the 1 from the checkbox to return 100% opacity or 0% depending on
the state of the switch. Here’s the tricky bit, how to get the 0 from the checkbox interpreted
as 100% opacity and the 1 as 0% opacity to apply to the layers for the alternate state.
For this I consulted an Oxford graduate and he solved it thusly:
so in my comp for the alternate state layers the code looks like this:
So there is now a single controller on Null 2 to switch between my day time and night time layers
with a keyframeable checkbox. Magic.