I want to use a mask to animate a path that I drew with the After Effects pen tool. Shouldn't I be able to draw another path on top of the first, and somehow animate its mask to reveal the layer beneath? I've attached a picture below that shows the stroked path that I want to be revealed, as if someone is drawing it around the circular magnet. How can I do this? Thanks for the help.
If it's the stroke/writeon you're trying to create, maybe the TRIM PATHS option in your shape layer will get you there.
Here's one way of doing it
Copy the Path property (not Path1) of your Shape Layer
Expose the Mask Path property
Alt-click the Shape Layer's Path property (for expressions) and pickwick to the Mask Path property.
This allows your to alter the shape of the mask and the stroke will adjust simultaneously
Add a Generate>Stroke effect to the Shape Layer
Set the Brush Size to be greater (just) than the width of your shape stroke
Change the Paint Style to Reveal Original Image
Keyframe the Start and/orEnd property to taste.