Issue with rigid body and modifiers dependent on transform #58044

New Issue

Mal Duffin · 2018-11-25T10:52:10+01:00

Mal Duffin commented

2018-11-25 10:52:10 +01:00

System Information
Windows 10, GTX1070

Blender Version
Broken: Blender 2.83
Working: Blender 2.79 ( <- Updated info )

Short description of error
When adding hair to a rigid body, the hair position doesn't update.

Exact steps for others to reproduce the error

In the Physics tab select rigid body
In the Particles tab create new Hair
Select Hair Dynamics
Play the animation.
The ball will fall, but the hair doesn't follow it.

Have a look at the attached blend - beside the rigid body cube, I've animated a second cubes position to fall, and the hair follows it correctly
hair_particles_on_rigid_body.blend.

**System Information** Windows 10, GTX1070 **Blender Version** Broken: Blender 2.83 Working: Blender 2.79 ( <- Updated info ) **Short description of error** When adding hair to a rigid body, the hair position doesn't update. **Exact steps for others to reproduce the error** - In the Physics tab select rigid body - In the Particles tab create new Hair - Select Hair Dynamics - Play the animation. The ball will fall, but the hair doesn't follow it. Have a look at the attached blend - beside the rigid body cube, I've animated a second cubes position to fall, and the hair follows it correctly [hair_particles_on_rigid_body.blend](https://archive.blender.org/developer/F5712545/hair_particles_on_rigid_body.blend).

Mal Duffin commented

2018-11-25 10:52:10 +01:00

Added subscriber: @MalDuffin

blender-admin commented

2018-11-25 10:52:10 +01:00

#68128 was marked as duplicate of this issue

blender-admin commented

2018-11-25 10:52:10 +01:00

#71011 was marked as duplicate of this issue

blender-admin commented

2018-11-25 10:52:10 +01:00

#69419 was marked as duplicate of this issue

blender-admin commented

2018-11-25 10:52:10 +01:00

#69407 was marked as duplicate of this issue

blender-admin commented

2018-11-25 10:52:10 +01:00

#66935 was marked as duplicate of this issue

blender-admin commented

2018-11-25 10:52:10 +01:00

#66828 was marked as duplicate of this issue

blender-admin commented

2018-11-25 10:52:10 +01:00

#60079 was marked as duplicate of this issue

blender-admin commented

2018-11-25 10:52:10 +01:00

#65541 was marked as duplicate of this issue

blender-admin commented

2018-11-25 10:52:10 +01:00

#63761 was marked as duplicate of this issue

Mal Duffin commented

2018-11-25 11:34:45 +01:00

Note that, if you carry out the above steps and skip 7), the ( non-hair ) particle effects do follow the cube.

Philipp Oeser commented

2018-11-27 10:36:32 +01:00

Added subscribers: @fclem, @Sergey, @lichtwerk

Philipp Oeser commented

2018-11-27 10:36:32 +01:00

Can confirm this.
This could just be a drawing issue (e.g. if you go into Particle Editmode the hair is actually in the right spot).

Havent checked code. If this drawing only, I would kindly ask @fclem to have a look, but it might also be one for @Sergey to check

Can confirm this. This could just be a drawing issue (e.g. if you go into Particle Editmode the hair is actually in the right spot). Havent checked code. If this drawing only, I would kindly ask @fclem to have a look, but it might also be one for @Sergey to check

Mal Duffin commented

2018-11-27 10:42:44 +01:00

Another interesting related issue. If you replace step 4) Rigid Body with 4a) Soft Body and optionally 4b) Toggle off Goal, then the hair particles do follow the new physics position of the cube when you press play after step 8)
So, hair seems to work with Soft Body physics updates and not Rigid Body physics updates.

Another interesting related issue. If you replace step 4) Rigid Body with 4a) Soft Body and optionally 4b) Toggle off Goal, then the hair particles do follow the new physics position of the cube when you press play after step 8) So, hair seems to work with Soft Body physics updates and not Rigid Body physics updates.

Mal Duffin commented

2019-02-04 17:33:11 +01:00

When in particle mode...

Hair appears at the position of the rigid body
, but ( if you enable hair dynamics )
Hair strands haven't moved, it's like they are showing the default non-simulated hair particle strand shape, rather than the actual simulated shape of the hairs.

In edit mode...

Hair doesn't move with the rigid body
but
Hair strands do move as if they are simulated

When in particle mode... - Hair appears at the position of the rigid body , but ( if you enable hair dynamics ) - Hair strands haven't moved, it's like they are showing the default non-simulated hair particle strand shape, rather than the actual simulated shape of the hairs. In edit mode... - Hair doesn't move with the rigid body but - Hair strands do move as if they are simulated

Georg Bernhard commented

2019-02-16 16:52:59 +01:00

Added subscriber: @gogo

Mal Duffin commented

2019-03-20 21:10:52 +01:00

@Sergey - I see you just fixed another issue with rigid bodies and particles, could you have a look at this one too?

Sergey Sharybin self-assigned this 2019-04-04 09:36:52 +02:00

Sergey Sharybin commented

2019-04-04 09:36:52 +02:00

Would need to have a closer look, but could be caused by the change in the evaluation order of rigid body, similar to #63028.

The issue here is that such setups are causing feedback loop in the system:

Hair is evaluated as a part of modifier stack
Modifier stack in this case needs to know object's world position
Rigid body defines the world position
Rigid body needs to know output of the modifier stack to perform proper collisions

This appeared to work in 2.7 better, but was always causing one frame offset during animation. Which isn't really helpful, since it causes self-intersections which are impossible to fix. Additionally, rendering motion blur becomes a huge issue in those configurations.

Would need to have a closer look, but could be caused by the change in the evaluation order of rigid body, similar to #63028. The issue here is that such setups are causing feedback loop in the system: - Hair is evaluated as a part of modifier stack - Modifier stack in this case needs to know object's world position - Rigid body defines the world position - Rigid body needs to know output of the modifier stack to perform proper collisions This appeared to work in 2.7 better, but was always causing one frame offset during animation. Which isn't really helpful, since it causes self-intersections which are impossible to fix. Additionally, rendering motion blur becomes a huge issue in those configurations.

Mal Duffin commented

2019-04-04 09:41:02 +02:00

Hi Sergey,

Thanks for having a look.

Hopefully it can be fixed, think of all the hairy domino simulations that need rendered! :P

Hi Sergey, Thanks for having a look. Hopefully it can be fixed, think of all the hairy domino simulations that need rendered! :P

Sergey Sharybin commented

2019-04-25 12:41:41 +02:00

Added subscribers: @gase12, @ZedDB

Brecht Van Lommel commented

2019-06-06 14:19:30 +02:00

Added subscribers: @keinerweiss, @StephenSwaney, @grosgood

Sergey Sharybin commented

2019-07-09 11:06:05 +02:00

Added subscribers: @dadou99, @sreich, @3di, @SmartySmart702, @brecht

Sergey Sharybin changed title from ~~Issue with adding hair to rigid body~~ to Issue with rigid body and modifiers dependent on transform

2019-07-09 11:06:25 +02:00

dan collins commented

2019-07-09 20:26:23 +02:00

Added subscriber: @badbytes

michael campbell commented

2019-07-12 20:45:59 +02:00

Just tested the release candidate and the bug is still here. Strangely it did appear to work once, with strange results, but after that it went back to only taking into account frame one of the rigid body simulation.

Sergey Sharybin commented

2019-07-16 14:14:55 +02:00

Added subscriber: @jricardo_rr

michael campbell commented

2019-07-31 11:44:53 +02:00

Guys, the entire physics system is broken, has this accidentally been overlooked? Really surprised 2.8 was released without this being fixed first.

check the file below which shows how this affects all interactions (not just hair).

physics broken.blend

Guys, the entire physics system is broken, has this accidentally been overlooked? Really surprised 2.8 was released without this being fixed first. check the file below which shows how this affects all interactions (not just hair). [physics broken.blend](https://archive.blender.org/developer/F7639303/physics_broken.blend)

Brecht Van Lommel commented

2019-07-31 11:46:44 +02:00

Please leave setting priorities to developers.

michael campbell commented

2019-07-31 11:57:59 +02:00

In #58044#740558, @brecht wrote:
Please leave setting priorities to developers.

OK Sorry, I just assumed the physics system no longer functioning would have been enough to warrant a 2.8 release delay, so I just wanted it to get immediate attention as I presumed this must have been lost in all of the bug reports over the past couple of months.

> In #58044#740558, @brecht wrote: > Please leave setting priorities to developers. OK Sorry, I just assumed the physics system no longer functioning would have been enough to warrant a 2.8 release delay, so I just wanted it to get immediate attention as I presumed this must have been lost in all of the bug reports over the past couple of months.

Zak Tab commented

2019-08-22 17:04:26 +02:00

Added subscriber: @zakleap

Zak Tab commented

2019-08-22 17:04:26 +02:00

Constraints are also ignored by rigid body physics. Animations have been greatly restricted by the lack of physics capability.

Philipp Oeser commented

2019-08-22 19:30:15 +02:00

I will dare raising this to High.

@brecht, @Sergey: shouldnt we try tackling this for 2.81?
(just correct me if I am wrong though...)

I will dare raising this to High. @brecht, @Sergey: shouldnt we try tackling this for 2.81? (just correct me if I am wrong though...)

Clément Foucault commented

2019-08-26 14:58:11 +02:00

Removed subscriber: @fclem

Sergey Sharybin commented

2019-09-02 16:36:52 +02:00

Added subscriber: @EricBu

Philipp Oeser commented

2019-09-03 09:09:06 +02:00

Added subscriber: @Eary

Zijun Zhou commented

2019-09-04 01:27:08 +02:00

I posted another similar post before being led to this one, I figured that after you do all the steps, don't play the animation yet, save the project, and close blender. Delete the .blend1 file beside the .blend file, the open it up again, and play the animation, the hair particles are now following the cube.

Base on that, I believe this has something to do with the .blend1 file. I am not a programmer, I don't know what the .blend1 file is, but I guess it is some kind of cache file. My theory is that although blender understands the hair should be following, the cache file (.blend1 file) is not updated, therefore the hair particles don't follow the cube as they should.

I posted another similar post before being led to this one, I figured that after you do all the steps, don't play the animation yet, save the project, and close blender. Delete the .blend1 file beside the .blend file, the open it up again, and play the animation, the hair particles are now following the cube. Base on that, I believe this has something to do with the .blend1 file. I am not a programmer, I don't know what the .blend1 file is, but I guess it is some kind of cache file. My theory is that although blender understands the hair should be following, the cache file (.blend1 file) is not updated, therefore the hair particles don't follow the cube as they should.

Davis Ethoien commented

2019-09-04 05:59:41 +02:00

Added subscriber: @davis095381-2

Davis Ethoien commented

2019-09-04 05:59:41 +02:00

In #58044#768622, @Eary wrote:
I posted another similar post before being led to this one, I figured that after you do all the steps, don't play the animation yet, save the project, and close blender. Delete the .blend1 file beside the .blend file, the open it up again, and play the animation, the hair particles are now following the cube.

Try again and reopen blender without deleting .blend1 file, because .blend1 file is just a backup of the saved .blend file.

> In #58044#768622, @Eary wrote: > I posted another similar post before being led to this one, I figured that after you do all the steps, don't play the animation yet, save the project, and close blender. Delete the .blend1 file beside the .blend file, the open it up again, and play the animation, the hair particles are now following the cube. > Try again and reopen blender without deleting .blend1 file, because .blend1 file is just a backup of the saved .blend file.

Zijun Zhou commented

2019-09-04 06:36:58 +02:00

In #58044#768697, @davis095381-2 wrote:

In #58044#768622, @Eary wrote:
I posted another similar post before being led to this one, I figured that after you do all the steps, don't play the animation yet, save the project, and close blender. Delete the .blend1 file beside the .blend file, the open it up again, and play the animation, the hair particles are now following the cube.

Try again and reopen blender without deleting .blend1 file, because .blend1 file is just a backup of the saved .blend file.

You are right, I tried it just now and it worked, perhaps it's not the .blend1 file, it is some kind of other problem. It is still the case though, that something is not updated, reloading Blender just refreshes it.

By the way, in order for it to work, set the shape to Mesh and set the source to Base under the "Collision" settings of the Rigid Body tab. I mentioned this in my post, which is closed now, it doesn't seem to be mentioned right here.

> In #58044#768697, @davis095381-2 wrote: >> In #58044#768622, @Eary wrote: >> I posted another similar post before being led to this one, I figured that after you do all the steps, don't play the animation yet, save the project, and close blender. Delete the .blend1 file beside the .blend file, the open it up again, and play the animation, the hair particles are now following the cube. >> > > Try again and reopen blender without deleting .blend1 file, because .blend1 file is just a backup of the saved .blend file. You are right, I tried it just now and it worked, perhaps it's not the .blend1 file, it is some kind of other problem. It is still the case though, that something is not updated, reloading Blender just refreshes it. By the way, in order for it to work, set the shape to Mesh and set the source to Base under the "Collision" settings of the Rigid Body tab. I mentioned this in my post, which is closed now, it doesn't seem to be mentioned right here.

Philipp Oeser commented

2019-09-06 12:48:43 +02:00

@Sergey : I have added this to 2.81 milestone (since it was set to "High"), mind checking again?

Fabian Raetz commented

2019-09-08 14:35:10 +02:00

Added subscriber: @fraetz

Sergey Sharybin was unassigned by Brecht Van Lommel

2019-09-17 15:30:00 +02:00

Brecht Van Lommel commented

2019-09-17 15:30:00 +02:00

This needs bigger design changes to the dependency graph and physics, and while it would be good if we can, it is not a requirement to be fixed for 2.81.