Thank you. I set up this pen to illustrate what I've been struggling with. At one point, I tried using a CSS clip-path, using a polygon for the mask. I could get it to animate, but only on Chrome and it wasn't working at all the way I wanted it.
Reading the docs on TweenLite.to(), I'm unsure whether GSAP also requires the target polygon data to have the same number of points, as was required by the (now deprecated) CSS implementation. For safety, I did so anyway.
Using GSAP, the mask is animating, but not yet the way I need it to. Reading the docs, I'm unsure on how to proceed :/. Just to make sure, what I need is for the clip-path polygon to appear from top to bottom, following its center path (if that makes sense).