Motion Paths not working on children objects.
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Description

System Information
Windows 10, i7 4770, Asus GTX 1060.

Blender Version
Broken: 2.78.5 hash 72c9141
Worked: I believe in 2.78 did work.

Short description of error
When an object is parented you cant get motion paths from it. It just wont calculate them.

Exact steps for others to reproduce the error
open a new file,
create 2 objects,
parent one to the other,
animate the parent,
go on the properties panel of the child > go motion paths, set your settings, and voilá no motion paths.

demo file:

Details

Type
Bug
Joshua Leung (aligorith) triaged this task as Normal priority.Jul 17 2017, 5:05 PM

Is this only for the new depsgraph? Testing with the old depsgraph seems fine here.

IIRC, Sergey made a fix in the 2.8 branch that removed the "fast" calculation method there, as the lack of depsgraph sorting meant that it wouldn't work anymore. However, I can't remember right now whether that fix got ported back to master.