Disney's Practical Guide to Path Tracing

Interestingly, one calculates what the camera sees.

Yep, and in 2D and 3D games the world moves, not the camera.

this is how ray tracing work since the beginning of computer graphics, path tracing is a type of ray tracing, and quite old one,it’s nothing new, or invented by disney.

I don’t think they said that. Though I hear Hyperion is awesome. It definitely looks awesome as Big Hero 6 was one of the most beautiful looking movies I’ve ever seen in-terms of lighting. I think the way it does ray sorting may be novel (I think I read that somewhere) but it’s still a path tracer.

Yep, the new thing about Hyperion is the ray sorting and batching which helps cache coherence a lot.
Details in here: https://disney-animation.s3.amazonaws.com/uploads/production/publication_asset/70/asset/Sorted_Deferred_Shading_For_Production_Path_Tracing.pdf