Generally render engines can do subframe mixing themselves, but the
purpose of subframe mixing in the simulation output node is to support
higher quality motion blur with bakes when there are topology-changing
operations after the simulation output node. Linear mixing can fill the
gaps while maintaining lower memory usage.
All point/instance domain attributes are mixed, but mixing is only
supported when the domain size is unchanged or when an `id` attribute
gives a mapping between elements. Theoretically it may be possible, but
nested instance geometry is not mixed in this commit due to the
difficulty of finding matching geometries across arbitrary instance
hierarchy changes. Attributes that are completely unchanged are ignored
using implicit sharing for better performance.
Pull Request: https://projects.blender.org/blender/blender/pulls/107599
e6e6fb3a62