I want to make an eyelid animation to slide up and down, but all of it to remain transparent. I don't know how to make an eyeball with its line to dissapear at the same line with eyelid as it goes up and down, remaining the transparency.
Take the upper eyelid layer(I believe it's a solid, masked and stroked), duplicate it, and remove the stroke. Place it above the pupil and change the pupils track matte(press F4 to switch to track mattes) to "alpha inverted.
If I was doing this, i would precomp both the eyeball and pupil, and have the precomps track matte be set to alpha inverted. Less masking work for you then.
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.
if i was doing this, i would likely create it as black outlines with white fills, and then either drop that comp into a new comp and add something like channel combiner, setting lightness to alpha only and checking the invert option, then adding the invert effect to make it black again. Or, add an adjustment layer to the top of the eye comp and add the same effects.
that way you are working with opaque layers that can cover other layers when needed, but still get the transparency in the end.