Bug 245658 – Provide dedicated functions for computation of from and to values for composite animations

• Status: NEW
• Component: Animations

[Antoine Quint]

Sam Weinig made a good point in https://github.com/WebKit/WebKit/pull/4674#issuecomment-1257318558:

> As a side note, so not needed for this PR, unless there is some great reason I don't quite understand to
> keep it the way it is, I think we should consider modeling these different compositing operations in a way
> that is easier to understand.
> I think the obvious way to do this would be to stop using the blend() functions for computing the used
> from/to for additive/accumulative animations, and instead add a new entry point. Obviously this would
> add a bit of extra boilerplate, but I think the clarity would be good in the end.

I also agree with this, especially since we call blend() with progress = 1 at all times.

[Radar WebKit Bug Importer]

<rdar://problem/100706662>