Render Lottie to UIImage with .coreAnimation

[artsimonyan23]

Render Lottie to the UIImage is not working correctly when I use the ".coreAnimation" rendering engine.

let view: LottieAnimationView = LottieAnimationView(name: "Any Lottie")
let renderer = UIGraphicsImageRenderer(bounds: view.bounds)
let image = renderer.image { rendererContext in
view.layer.render(in: rendererContext.cgContext)
}

When the rendering engine is .mainThread, the image is correct. On case .coreAnimation all Lottie components' x and y coordinates are (0, 0).

[calda]

This is a known problem with the Core Animation rendering engine.

The CA engine animates by playing CAAnimations. These animations don't actually affect the appearance of the animation view's layer -- they only affect the appearance of the view's layer.presentation(). Because of this, the view appears blank when rendered using view.layer.render(in:).

There are two possible workarounds:

1. Render the image using view.layer.presentation()?.render(in:) instead. The presentation layer is only available if the view is currently being rendered on-screen in a UIWindow. This is probably not a problem in most application use cases, but can be tricky in headless use cases like snapshot testing (we've made this work though, here's an example).
2. Use the Main Thread rendering engine instead, in cases where you expect to render the view into an image.

I believe this is a fundamental limitation from using CAAnimations. If anyone is aware of an implementation workaround that makes this work automatically, I'd love to hear it.