For AnimationWorklet, we require some form of ScrollTimeline interface to be available so that scroll-based animations can be created[0].

As of the date of bug creation, there is a ScrollTimeline API specified in a WICG[1], which is replicated below, but it is not yet stable. However for the first implementation of AnimationWorklet we are happy to implement and use a simpler draft version, and update as the spec solidifies.

Current spec for ScrollTimeline:

enum ScrollDirection {
  "auto",
  "block",
  "inline",
  "horizontal",
  "vertical"
};

enum ScrollTimelineAutoKeyword { "auto" };

dictionary ScrollTimelineOptions {
  Element scrollSource;
  ScrollDirection orientation = "auto";
  DOMString startScrollOffset = "auto";
  DOMString endScrollOffset = "auto";
  (double or ScrollTimelineAutoKeyword) timeRange = "auto";
  FillMode fill = "none";
};

[Constructor(optional ScrollTimelineOptions options)]
interface ScrollTimeline : AnimationTimeline {
  readonly attribute Element scrollSource;
  readonly attribute ScrollDirection orientation;
  readonly attribute DOMString startScrollOffset;
  readonly attribute DOMString endScrollOffset;
  readonly attribute (double or ScrollTimelineAutoKeyword) timeRange;
  readonly attribute FillMode fill;
};



Our first step should be to identify what simplified API we actually *need* for AnimationWorklet.


[0]: https://github.com/WICG/animation-worklet/blob/gh-pages/WIP.md

[1]: https://wicg.github.io/scroll-animations/#scrolltimeline-interface