difference in rendering between .coreAnimation and .mainThread

[mobiletoly]

Hi
When I use

LottieConfiguration.shared.renderingEngine = .mainThread

configuration - then animation seems to be fine. But when switch to newer .coreAnimation then animation is off. Recordings and lottie JSON files are attached.

Which Version of Lottie are you using?

Lottie 4.2.0

Expected Behavior

For .coreAnimation not to mess up the animation (video is attached)

rendering-mainThread.mov

Actual Behavior

Video is attached

rendering-coreAnimation.mov

Animation JSON

data.json.zip

[calda]

Are you testing with renderingEngine: .coreAnimation or renderingEngine: .automatic?

It's expected that renderingEngine: .coreAnimation will sometimes be incorrect. You should prefer using renderingEngine: .automatic, which falls back to the Main Thread rendering engine if it detects the Core Animation rendering engine doesn't support the animation.

[mobiletoly]

yes, I forgot to mention that tested with .automatic as well - same wrong result.

[qingqingqingli]

Just wanna add to this. I'm also experiencing this issue. coreAnimation mode does not render the animation smoothly.

[calda]

This appears to be an issue with how Core Animation itself is interpolating the transform keyframes. If we force this animation to use the expensive "manual interpolation" codepath then the legs are positioned correctly. This introduces other issues, and I'm also not sure how to detect this case dynamically (e.g. we wouldn't want to just "always" use the expensive codepath, because that would hurt performance for all other animations).

For now, using the main thread rendering engine is a good workaround.