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Linking empties with rigid body constraints into new scene will result in losing constraint settings
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Description

System Information
Win7 x64

Blender Version
Broken: 2.74 and below

Short description of error
Linking empties with rigid body constraints attached to them into a newly fresh scene will result in losing those constraint settings, as opposed to linking rigid body objects which works.

Exact steps for others to reproduce the error

  • Add rigid body to default cube (only required to create "RigidBodyWorld")
  • Add empty to scene
  • Add rigid body constraint to empty
  • Add new scene
  • Link empty from original scene to new scene

The empty in the new scene will now lack the constraint settings. In contrast if you link the cube as well, its rigid body settings will be kept. Looks like inconsistent behaviour.

BTW, would be nice if rigid body tools' "copy from active" would work also on constraint objects.

Details

Type
Bug

Event Timeline

Kai Kostack (kaikostack) raised the priority of this task from to Needs Triage by Developer.
Kai Kostack (kaikostack) updated the task description. (Show Details)
Kai Kostack (kaikostack) set Type to Bug.

Not sure, but looks like I would expect it. It doesn't make much sense to have a constraint to an object that isn't there at all. @Sergej Reich (sergof), what would you say?

Julian Eisel (Severin) lowered the priority of this task from Needs Triage by Developer to Normal.Mar 23 2015, 5:24 PM

Let me correct the report then as follows.

Instead of:

  • Link empty from original scene to new scene

Do:

  • Add a second cube to original scene
  • Assign cubes to constraint
  • Link empty + cubes from original scene to new scene

I hope now it makes more sense to you.

I see that the constaints are getting cleared, but that would be considered as a todo. I'd still like to hear Sergej's voice on that though.

I have to correct the report again. Apparently when linking to the new scene both rigid body and constraint settings will be linked as well. But if you now unlink both from the original scene the settings in the second scene are gone too. I guess they should be copied then?

Linking with rigid bodies is tricky, afair we decided that you counldn't link individual rigid body objects but could link entire scenes containing rigid bodies.
The problem is that the rigid body world belongs to the scene which causes all sorts of trouble for linking.
If you need individual objects you have to bake. Otherwise keep all objects that belong to one simulation in one scene.
Not sure if the unlinking in this case is a bug though, I don't really have this stuff in my head anymore and can't tell what is good behaviour for linked objects in blender.

The unlinking issue can be harmful to your work. Think of one who would like to move a complex simulation rig into a different scene for logistic reasons, everything looks perfect for the user as everything appears to work. Now he deletes the simulation in the original scene and saves his work, unknowingly that he just destroyed his simulation which he considered to be safe in the other scene.

@Kai Kostack (kaikostack), we're not suggesting this isn't useful, but this is indeed quite complicated w.r.t. linking.

I would move this to TODO, however realistically I don't think this is going to be supported, so documenting as a known-limitation instead.

rBM774, https://www.blender.org/manual/data_system/linked_libraries.html#known-limitations