[scroll-animations] ScrollTimeline.currentTime precision can easily surpass the recommended microseconds precision

[majido]

In Web Animation spec, time values (e.g., duration, current time) etc, are specified in milliseconds. Additionally the specification recommends implementations to be able to support precision up to microseconds.

The web animation spec, work fine for regular wall-clock time based animations where
microseconds precision is plenty. This however, can quickly become problematic with ScrollTimeline.

The computation of ScrollTimeline current time depends on timeRange (in milliseconds) and scroll range. Specifically

current time = scroll offset / scroll range × effective time range

This means that with event a medium sized scroll range (e.g., 1000px) and a small timeRange (e.g., 1ms) it is possible to produce time values smaller than one microseconds. Which means having distinct scroll offsets that map to the same time values. This results in undesirable jitters for any animations that wants animation wants to position object relative to scroll offset as represented by ScrollTimeline.currentTime.

[majido]

I think we need at least some sort of warning in spec so that users will be mindful of the impact of their timeRange on the precision of produces time values.

[flackr]

ScrollTimelines no longer convert scroll to milliseconds, so this is no longer a concern developers need to worry about.