Update isVisible

[SalvoDiFede]

Using box.getBoundingClientRect() for better compatibility, please check and test before commit to main branch :-)

[attilaolah]

This looks very cool, but apparently the tests don't like it. I'll dig into that and see why.

Maybe we can also kill that funky offsetTop method then.

[jlmakes]

I tried implementing element.getBoundingClientRect() into ScrollReveal v3.0.0, and I can confirm it's likely not suitable for our scrolling animation libraries—the visibility factors in CSS transformations, whereas element offset does not.

This is most noticeable with large translations… where in some cases, the element will either be visible/invisible at the same time (based on the time at which is checked during animation), or never be visible at all.

A simple example can be seen here ScrollReveal Issue #193

Hope this helps! 🙇