How to get a layer's position?

[ir-fuel]

I've been looking around everywhere and it seems not to be documented in the official Lottie docs, and through Google I find plenty of out of date info.

The issue is the following: I have a Lottie animation that's supposed to cover a big part of my screen, containing a shape layer named "Shape Layer 11". I want to use that layer's (relative) position to position it on a certain point on my screen. I checked with the Lottie Editor and can see the values I want, I can even see them in Xcode when introspecting the animation object.

If I know the original bounding box of the animation, and the position in that box of the layer, I know how to exactly position the layer so it's on the right position on screen using relative positioning.

The information I found talked about using a LottieAnimationView and using:

            let positionKeypath = AnimationKeypath(keypath: "Shape Layer 11.Transform.Position")
            let currentValue = view.getValue(for: positionKeypath, atFrame: .zero)

But I just discovered this is no longer supported in the new rendering engine.

How do we introspect a Lottie animation file? There is no info about this in the documentation.

These are the values I want to access:

[calda]

Have you tried this same code but using the main thread rendering engine instead?

[ir-fuel]

Yes, and that works. I would like to know what the way of doing this is when using the other rendering engine now.

What I do right now is load the animation in a view that uses the main thread engine, extract the data I need, throw everything away and then use the animation in the optimized rendering engine, but that seems a bit ridiculous?

[calda]

I would suggest just always using the main thread rendering engine for that use case.

The Core Animation rendering engine doesn't currently support reading / inspecting the current state of the animation via key paths. This may conceivably be possible by reading the current state of the layers' presentation layer, but the keypath system in the CA engine is not architected to enable that.

Potentially, it could make sense to have the Core Animation rendering engine tag each layer with its keypath somehow, which you could then retrieve and introspect.

[ir-fuel]

For me it's not about getting real-time feedback. It's about getting the state at "frame 0" so I can correctly position a big animation on the screen. It's something that needs to start from a given point (a button) but the animation goes over the entire screen. I just need to position it before it starts.

[calda]

The layers all have "real" frames of .zero. The size and position are provided by CAAnimations, which are only reflected in the presentation layers. So, to access the frame, it would have to be read off of the presentation layer.

[ir-fuel]

Another issue is the complete lack of documentation when it comes to introspecting animations. I found info on how to modify values using valueproviders, but how to read/introspect a Lottie animation file isn't documented anywhere.