Rigid Body Constraint on passive object causes dependency cycle #78952

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RedMser · 2020-07-15T17:16:43+02:00

RedMser commented

2020-07-15 17:16:43 +02:00

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 446.14

Blender Version
Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-07-08 20:30, hash: 31bc76ea4e
Worked: 2.79b

Short description of error
Adding a Rigid Body Constraint to a (passive) Rigid Body Object causes a dependency cycle.

I don't know if this is a big "problem" (any performance issues, breaking more complex physics setups when doing this), but considering how this setup is recommended as an alternative to using an empty object in the manual, it seems worth looking into.

Exact steps for others to reproduce the error
Load this file in Blender 2.90:
bug_depsgraph_rigidbodyconstaints.blend
For easier comparison of both methods, two pairs of objects exists. FirstC/SecondC cause the deps cycle (with FirstC having the constraint), while First/Second uses a separate empty for the constraint which works fine.

The same setup does not have any deps cycles in Blender 2.79b (did not try 2.80/81/82), see this file:
bug_depsgraph279_rigidbodyconstraints.blend

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 446.14 **Blender Version** Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-07-08 20:30, hash: `31bc76ea4e` Worked: 2.79b **Short description of error** Adding a Rigid Body Constraint to a (passive) Rigid Body Object causes a dependency cycle. I don't know if this is a big "problem" (any performance issues, breaking more complex physics setups when doing this), but considering how this setup is [recommended as an alternative to using an empty object in the manual](https://docs.blender.org/manual/en/latest/physics/rigid_body/constraints/introduction.html#physics-menu), it seems worth looking into. **Exact steps for others to reproduce the error** Load this file in Blender 2.90: [bug_depsgraph_rigidbodyconstaints.blend](https://archive.blender.org/developer/F8697171/bug_depsgraph_rigidbodyconstaints.blend) For easier comparison of both methods, two pairs of objects exists. FirstC/SecondC cause the deps cycle (with FirstC having the constraint), while First/Second uses a separate empty for the constraint which works fine. The same setup does not have any deps cycles in Blender 2.79b (did not try 2.80/81/82), see this file: [bug_depsgraph279_rigidbodyconstraints.blend](https://archive.blender.org/developer/F8697180/bug_depsgraph279_rigidbodyconstraints.blend)

RedMser commented

2020-07-15 17:16:43 +02:00

Added subscriber: @RedMser

Richard Antalik commented

2020-07-16 00:36:47 +02:00

Added subscriber: @iss

Richard Antalik commented

2020-07-16 00:36:47 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Richard Antalik commented

2020-07-16 00:36:47 +02:00

I don't know if this is a big "problem" (any performance issues, breaking more complex physics setups when doing this), but considering how this setup is recommended as an alternative to using an empty object in the manual, it seems worth looking into.

Can you cite where this is suggested? I don't really see it there.

Comparison with 2.79 behavior isn't really valid, because it used old dependency graph.

>I don't know if this is a big "problem" (any performance issues, breaking more complex physics setups when doing this), but considering how this setup is recommended as an alternative to using an empty object in the manual, it seems worth looking into. Can you cite where this is suggested? I don't really see it there. Comparison with 2.79 behavior isn't really valid, because it used old dependency graph.

RedMser commented

2020-07-16 00:44:25 +02:00

Can you cite where this is suggested? I don't really see it there.

See the section "Physics Menu":

"Also you can create Rigid Body Constraint on one of the two constrained objects with Rigid Body Constraint button of the Physics tab in the Properties editor. [...] This way, there are no empty object created for the constraint. The role of the empty object is put on this object. The constrained object can be then set as Passive type for better driving the constrain."

Comparison with 2.79 behavior isn't really valid, because it used old dependency graph.

Fair point. I just wanted to ensure the report wouldn't get invalidated because it didn't include any information about the "Worked" Blender version.

> Can you cite where this is suggested? I don't really see it there. See the section "Physics Menu": "Also you can create Rigid Body Constraint on one of the two constrained objects with Rigid Body Constraint button of the Physics tab in the Properties editor. [...] This way, there are no empty object created for the constraint. The role of the empty object is put on this object. The constrained object can be then set as Passive type for better driving the constrain." > Comparison with 2.79 behavior isn't really valid, because it used old dependency graph. Fair point. I just wanted to ensure the report wouldn't get invalidated because it didn't include any information about the "Worked" Blender version.

Richard Antalik commented

2020-07-16 01:59:29 +02:00

Added subscriber: @Sergey

Richard Antalik commented

2020-07-16 01:59:29 +02:00

In #78952#979860, @RedMser wrote:

Can you cite where this is suggested? I don't really see it there.

See the section "Physics Menu":

"Also you can create Rigid Body Constraint on one of the two constrained objects with Rigid Body Constraint button of the Physics tab in the Properties editor. [...] This way, there are no empty object created for the constraint. The role of the empty object is put on this object. The constrained object can be then set as Passive type for better driving the constrain."

Perhaps I am reading this wrong(too literaly), but you haven't created constraint on "one of two constrained objects", but on unconstrained object.

I don't know much about limitations here, but when I tried to follow manual literaly, there seems to be no dependency cycle. In following file I created constraint on object Cube.
#78952.blend

But perhaps this is another bug and info in manual is outdated as well. @Sergey do you know how this should work? I can imagine this working either way really.

> In #78952#979860, @RedMser wrote: >> Can you cite where this is suggested? I don't really see it there. > > See the section "Physics Menu": > > "Also you can create Rigid Body Constraint on one of the two constrained objects with Rigid Body Constraint button of the Physics tab in the Properties editor. [...] This way, there are no empty object created for the constraint. The role of the empty object is put on this object. The constrained object can be then set as Passive type for better driving the constrain." Perhaps I am reading this wrong(too literaly), but you haven't created constraint on "one of two constrained objects", but on unconstrained object. I don't know much about limitations here, but when I tried to follow manual literaly, there seems to be no dependency cycle. In following file I created constraint on object Cube. [#78952.blend](https://archive.blender.org/developer/F8698167/T78952.blend) But perhaps this is another bug and info in manual is outdated as well. @Sergey do you know how this should work? I can imagine this working either way really.

Richard Antalik commented

2020-07-16 02:06:59 +02:00

Changed status from 'Needs User Info' to: 'Needs Triage'

Richard Antalik commented

2020-07-16 02:22:33 +02:00

Well actually I reopened my file and there is dependecy cycle as well, so I guess ignore last comment. This means that information in manual is incorrect then.

Richard Antalik commented

2020-07-22 06:56:43 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Richard Antalik commented

2020-07-22 06:56:43 +02:00

I have worked on another report where constraint was placed on empty which also produces dependency cycle. I think this is very likely bug so I will confirm this

RedMser commented

2020-07-30 19:36:02 +02:00

The problem has been fixed by 8dc2fbd7b6. I don't have any dependency cycles in the original blend file anymore and the constraints work as expected.

The problem has been fixed by 8dc2fbd7b6. I don't have any dependency cycles in the original blend file anymore and the constraints work as expected.

Richard Antalik commented

2020-07-30 19:40:44 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Richard Antalik closed this issue

2020-07-30 19:40:44 +02:00

Richard Antalik self-assigned this 2020-07-30 19:40:44 +02:00

Richard Antalik commented

2020-07-30 19:40:44 +02:00

Thanks for info. good to hear things are working

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Rigid Body Constraint on passive object causes dependency cycle #78952