Quote Originally Posted by Nattsurf View Post
Great just wonder how they able to make this kind of functions
If you're asking about Spine -- that's because Spine has a mostly-documented "interchange" format for animations, using JSON. We read it, convert to X3D graph (our scene graph), and we're happy

In any case, the engine is open-source, https://github.com/castle-engine/castle-engine/ . So you can see how we're doing everything