angular directive for scroll-based actions. An element with the
directive can be associated with any number of scroll positions. At each scroll
position you can trigger any number of actions. An action can call any function
on the scope, add or remove a class to the element, and/or broadcast an event
from the element's scope . You can also easily define your own actions if the
built-in actions aren't enough.
spark-scroll-animate directive includes all of the features
spark-scroll plus the ability to animate CSS properties in sync
with the browser scroll position.