Object Group Reorder #40741

New Issue

Philip Holzmann · 2014-06-21T12:19:12+02:00

Philip Holzmann commented

2014-06-21 12:19:12 +02:00

System Information
Windows 7 64bit, 16 GB RAM, AMD 8 Cores 3.11 GHz, AMD Radeon HD 6450

Blender Version
Broken: (2.70a f93bc76)

Short description of error
In a hair particle system which renders a group, the objects are sometimes reordered after saving and reloading.

Exact steps for others to reproduce the error
test.blend
In the attached file in camera view, the big 'L' should be on the left side of the big 'R'. That's the way the file was saved.
But after reloading the file, they are sometimes swapped.

To correct the order, remove both little letters from the group, and then first add the little 'R' to the group and then the little 'L'. But after saving, the order is wrong again.

**System Information** Windows 7 64bit, 16 GB RAM, AMD 8 Cores 3.11 GHz, AMD Radeon HD 6450 **Blender Version** Broken: (2.70a f93bc76) **Short description of error** In a hair particle system which renders a group, the objects are sometimes reordered after saving and reloading. **Exact steps for others to reproduce the error** [test.blend](https://archive.blender.org/developer/F95124/test.blend) In the attached file in camera view, the big 'L' should be on the left side of the big 'R'. That's the way the file was saved. But after reloading the file, they are sometimes swapped. To correct the order, remove both little letters from the group, and then first add the little 'R' to the group and then the little 'L'. But after saving, the order is wrong again.

Philip Holzmann commented

2014-06-21 12:19:12 +02:00

Changed status to: 'Open'

Philip Holzmann commented

2014-06-21 12:19:12 +02:00

Added subscriber: @Foaly

Lukas Tönne was assigned by Sergey Sharybin

2014-06-27 10:54:26 +02:00

Sergey Sharybin commented

2014-06-27 10:54:26 +02:00

Added subscribers: @LukasTonne, @Sergey

Sergey Sharybin commented

2014-06-27 10:54:26 +02:00

@LukasTonne, is it something you're familiar with?

Lukas Tönne commented

2014-06-27 12:06:32 +02:00

Changed status from 'Open' to: 'Archived'

Lukas Tönne closed this issue

2014-06-27 12:06:32 +02:00

Lukas Tönne commented

2014-06-27 12:06:32 +02:00

This is a known limitation of the particle code: It uses objects from the group randomly, but in order to make that repeatable it must expect the group to have some fixed ordering in the first place. This is not well defined, rather than lists groups are conceptually sets, without a defined order (only our use of ListBase structs doesn't enforce the distinction). The dependency graph or other code may reshuffle groups.

A workaround for the problem is to enable the Use Count option, which defines its own ordering instead of relying on the group. This is the only feasible implementation of such group object selection anyway, the random group element picking just doesn't allow repeatable results.

This is a known limitation of the particle code: It uses objects from the group randomly, but in order to make that repeatable it must expect the group to have some fixed ordering in the first place. This is not well defined, rather than *lists* groups are conceptually *sets*, without a defined order (only our use of `ListBase` structs doesn't enforce the distinction). The dependency graph or other code may reshuffle groups. A workaround for the problem is to enable the **Use Count** option, which defines its own ordering instead of relying on the group. This is the only feasible implementation of such group object selection anyway, the random group element picking just doesn't allow repeatable results.

Philip Holzmann commented

2014-06-27 12:45:59 +02:00

Thank you!
The use count option works. Now I don't have to recreate the groups every time I open my scene.

Thank you! The use count option works. Now I don't have to recreate the groups every time I open my scene.

Philip Holzmann commented

2014-06-27 12:46:16 +02:00

Removed subscriber: @Foaly

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Object Group Reorder #40741