Lottie 4.0 more custom value providers for Core Animation engine

[opfeffer]

Hi there- loved reading the announcement about the 4.0 release and the introduced performance improvements using CoreAnimation. I immediately went and updated our dependency from 3.4.3 to see the improvements in our app.

Unfortunately, I noticed that 4.0 still only supports the value provider for colors but no other types (see ValueProviderStore.swift).

I saw this comment in the 3.4 announcement discussion indicating that other custom value provider types were possibly coming in future releases. Is that still the plan?

Congrats again to shipping a new major version of the library. Very excited to see its still being actively maintained! 👏

[calda]

Ideally this would be implemented eventually! I haven't prioritized it because I'm not really familiar with the use cases for this, other than customizing colors. Could you share information about your use case?

[opfeffer]

One trivial example is our use of FloatValueProviders for *.Opacity transform layers to dynamically hide and show certain elements of animation. This article might be a good overview of other use cases such as scale transforms..

[calda]

That opacity use case makes a ton of sense! Could you file an issue for this? I'll find a chance to add support for opacity here.

For now I probably plan on adding support for individual use cases as folks request them. That keeps things a bit more manageable, and will let us remove support for features that don't have much/any usage.

[opfeffer]

Done: #1837