I want to make a letter made up of diagonal stripes that are moving downward (Imagine a barber shop pole).
I have the diagonal stripes on a layer which I have added a mask to. The mask ("Mask 1") is the shape of the letter "K."
How do I animate that layer of stripes while my mask remains in the same spot?
The easiest way would be to add your mask to a solid above your moving shapes, animate that layer(either the mask path or just the layer position), then set your shape layers track matte to "alpha matte"
Johnny Cuevas, Editor
"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.
What you could do is use the grid effect. (under generate) set tge geight to ..well whatever you need, and width to 2000 so vertical lines are outside the view. Rotate the layer as you see fit and use the centre point to animate.. Then either use preserve transparancy or the text as a track matte, depending on what your comp looks like.