Copy Rotation object constraint not working in local space #91117

New Issue

Demeter Dzadik · 2021-09-01T18:34:52+02:00

Demeter Dzadik commented

2021-09-01 18:34:52 +02:00

System Information
Operating system: Linux-5.8.0-7642-generic-x86_64-with-glibc2.32 64 Bits
Graphics card: GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.56

Blender Version
Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-08-31 17:17, hash: 838b6ec48a
Worked: Not sure actually.

Short description of error
While trying to theorize about how rigging nodes would work, I realized I either have no idea how constraints work, or there is a bug where "Local Space" doesn't work for object constraints. I'm still a bit unsure.

Exact steps for others to reproduce the error

cubes.blend
Cube A has a local Copy Rotation constraint targetting Cube B, yet it's not copying the rotation at all.
Disable the Copy Rotation and enable the Copy Location constraint. It copies the location, but when rotating Cube A, it seems that the copied location is applied after the rotation, which seems at the very least inconsistent with how bones do it.

Perhaps this was always like this... but I can't wrap my head around how any of this makes sense!

**System Information** Operating system: Linux-5.8.0-7642-generic-x86_64-with-glibc2.32 64 Bits Graphics card: GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.56 **Blender Version** Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-08-31 17:17, hash: `838b6ec48a` Worked: Not sure actually. **Short description of error** While trying to theorize about how rigging nodes would work, I realized I either have no idea how constraints work, or there is a bug where "Local Space" doesn't work for object constraints. I'm still a bit unsure. **Exact steps for others to reproduce the error** - [cubes.blend](https://archive.blender.org/developer/F10360915/cubes.blend) - Cube A has a local Copy Rotation constraint targetting Cube B, yet it's not copying the rotation at all. - Disable the Copy Rotation and enable the Copy Location constraint. It copies the location, but when rotating Cube A, it seems that the copied location is applied after the rotation, which seems at the very least inconsistent with how bones do it. Perhaps this was always like this... but I can't wrap my head around how any of this makes sense!

Demeter Dzadik commented

2021-09-01 18:34:52 +02:00

Added subscriber: @Mets

Philipp Oeser commented

2021-09-02 10:14:13 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2021-09-02 10:14:13 +02:00

Works if the cubes have parents:
cubes parented.blend

I think it is related to 7728bfd4c4 / f881162f81 (but still trying to figure out what is happening)

Works if the cubes have parents: [cubes parented.blend](https://archive.blender.org/developer/F10362619/cubes_parented.blend) I think it is related to 7728bfd4c4 / f881162f81 (but still trying to figure out what is happening)

Philipp Oeser commented

2021-09-02 10:28:38 +02:00

Yep, have a build where this was not reverted (da6929488a) and there it works (without parents).

Now what does the manual say [not very helpful since it doesnt really tell us what the behavior is ;)]:

For objects without a parent Local Space has a special meaning, different from the
normal behavior of local space for bones or objects that have a parent. This behavior is
kept for backward compatibility, but may be removed in the future and shouldn't be used.

This is from the release notes https://wiki.blender.org/wiki/Reference/Release_Notes/2.82/Rigging#Constraints

Previously Local Space of parentless objects was interpreted as "World Space but then with the object's own rotation also applied"

From 599c8a2c8e

... special case we are doing here re 'Local'
space of parent-less objects. In that case, local space should be the same as
world one, but instead we apply the object rotation to it...

Eh, I think that means that own rotation pretty much cancels itsef out (if it is already applied to the local space?)

Yep, have a build where this was not reverted (da6929488a) and there it works (without parents). Now what does the manual say [not very helpful since it doesnt really tell us what the behavior is ;)]: ``` For objects without a parent Local Space has a special meaning, different from the normal behavior of local space for bones or objects that have a parent. This behavior is kept for backward compatibility, but may be removed in the future and shouldn't be used. ``` This is from the release notes https://wiki.blender.org/wiki/Reference/Release_Notes/2.82/Rigging#Constraints ``` Previously Local Space of parentless objects was interpreted as "World Space but then with the object's own rotation also applied" ``` From 599c8a2c8e ``` ... special case we are doing here re 'Local' space of parent-less objects. In that case, local space should be the same as world one, but instead we apply the object rotation to it... ``` Eh, I think that means that own rotation pretty much cancels itsef out (if it is already applied to the local space?)

Philipp Oeser commented

2021-09-02 10:33:34 +02:00

@Mets : if this explains it for you, I think we have to close, since

...but may be removed in the future and shouldn't be used

@Mets : if this explains it for you, I think we have to close, since > ...but may be removed in the future and shouldn't be used

Demeter Dzadik commented

2021-09-02 14:33:49 +02:00

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

Demeter Dzadik closed this issue

2021-09-02 14:33:49 +02:00

Demeter Dzadik commented

2021-09-02 14:33:49 +02:00

Thanks a lot for hunting this down! Yeah I suppose it can be closed, I will add this to my notes and try to nudge some devs to clean this up sometime. It sounds like the currently existing "Local Space" option should become a legacy option, and a new option added that works consistently with how bones do.

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Copy Rotation object constraint not working in local space #91117