Compound Physics - Origin does not shift. #40340

New Issue

Jacob Merrill · 2014-05-24T18:14:03+02:00

Jacob Merrill commented

2014-05-24 18:14:03 +02:00

Compound_center_of_gravity_bug.blend

CompoundParentingPhysicsBug.blend

System Information
Any

Blender Version
2.7a

Short description of error
Origin does not shift on compound parent, and if a compound physics bounded item is parented to another compound, it leaves an invisible copy of the physics item of the child.

Exact steps for others to reproduce the error
press play

in example two the instructions are included in a text.

[Compound_center_of_gravity_bug.blend](https://archive.blender.org/developer/F90606/Compound_center_of_gravity_bug.blend) [CompoundParentingPhysicsBug.blend](https://archive.blender.org/developer/F90607/CompoundParentingPhysicsBug.blend) **System Information** Any **Blender Version** 2.7a **Short description of error** Origin does not shift on compound parent, and if a compound physics bounded item is parented to another compound, it leaves an invisible copy of the physics item of the child. **Exact steps for others to reproduce the error** press play in example two the instructions are included in a text.

Jacob Merrill commented

2014-05-24 18:14:03 +02:00

Changed status to: 'Open'

Jacob Merrill commented

2014-05-24 18:14:03 +02:00

Added subscriber: @JacobMerrill-1

Raf Colson commented

2014-05-24 18:32:51 +02:00

Added subscriber: @raco

Raf Colson commented

2014-05-24 18:32:51 +02:00

In example two probably also another issue presents itself. In the Physics Properties both Cubes have 'Compound' checked. One is parented to the other, with 'Compound' checked in the Parent Actuator. This causes only the visible mesh to be updated. This is a different issue than the center of gravity bug. Just for your information.

Bastien Montagne changed title from ~~Compound Physics - Origin does not shift, and if a compound physics bounded item is parented to another compound, it leaves an invisible copy of the physics item of the child.~~ to Compound Physics - Origin does not shift.

2014-05-24 21:15:04 +02:00

Mitchell Stokes commented

2014-06-05 03:08:19 +02:00

Added subscriber: @Moguri

Mitchell Stokes commented

2014-06-05 03:08:19 +02:00

In Bullet, the shape's transform matrix is it's "center." When adding objects to a compound shape, we don't adjust the parent's transform matrix. We could probably do this, but it requires digging through our physics code and possibly breaking games. A work around is to just create a small, invisible cube that you want to be your "center of gravity" and make it the root of the compound object. Any further objects added to the compound shape will be added relative to the root.

Inês Almeida commented

2014-06-27 23:10:12 +02:00

Added subscriber: @brita

Mitchell Stokes commented

2014-07-01 06:20:46 +02:00

Changed status from 'Open' to: 'Archived'

Mitchell Stokes closed this issue

2014-07-01 06:20:46 +02:00

Mitchell Stokes self-assigned this 2014-07-01 06:20:46 +02:00

Mitchell Stokes commented

2014-07-01 06:20:46 +02:00

Closing this as "Won't Fix". The supplied work-around I think is acceptable, and trying to "fix" this bug could just result in more physics bugs (and possibly breaking existing games).

Jacob Merrill commented

2014-07-01 21:27:27 +02:00

What about adding a command

joinCompoundObjects([list objects]) that does the for-mentioned

Get center of mass

Get Mass

Add compound object "Root"

Parent top of Hierarchy chain to root?

(or something smarter)

using a python function or class?

What about adding a command joinCompoundObjects([list objects]) that does the for-mentioned Get center of mass Get Mass Add compound object "Root" Parent top of Hierarchy chain to root? (or something smarter) using a python function or class?

Raf Colson commented

2014-07-02 02:17:50 +02:00

I agree it would get too messy, but I don't think this work-around is perfect enough, let alone fitted to add as a function to the API. I don't think you can't even call it a work-around, because the result is far from perfect. There's still the collision mesh of the added 'parent' object to consider. Even if this would be cube as small as a grain, its vertexes would still interfere with collision. Here's a blend to illustrate this: Compound_centroid_work-around_flaw.blend

A solution for this maybe would be to add compatibility with Material Physics for Compound objects. Currently if the Compound parent would have a material with Physics disabled, this would cause all added geometry to have no Physics enabled as well. So if Compound parenting would also take into consideration the Materials of the children, then we could have a complete work-around.

I agree it would get too messy, but I don't think this work-around is perfect enough, let alone fitted to add as a function to the API. I don't think you can't even call it a work-around, because the result is far from perfect. There's still the collision mesh of the added 'parent' object to consider. Even if this would be cube as small as a grain, its vertexes would still interfere with collision. Here's a blend to illustrate this: [Compound_centroid_work-around_flaw.blend](https://archive.blender.org/developer/F96254/Compound_centroid_work-around_flaw.blend) A solution for this maybe would be to add compatibility with Material Physics for Compound objects. Currently if the Compound parent would have a material with Physics disabled, this would cause all added geometry to have no Physics enabled as well. So if Compound parenting would also take into consideration the Materials of the children, then we could have a complete work-around.

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Compound Physics - Origin does not shift. #40340