https://obi.virtualmethodstudio.com/forum/ Mon, 07 Sep 2026 06:41:28 +0000 MyBB https://obi.virtualmethodstudio.com/forum/thread-4647.html Thu, 03 Sep 2026 09:13:08 +0200 nakai]]> https://obi.virtualmethodstudio.com/forum/thread-4647.html
I found two contact-related issues that appear to depend on the number of substeps in Obi Rope 6.5.4 using the Burst backend.

Test setup:

- Rod mass: 2.1 kg (21 particles, 0.1 kg each)
- Fixed timestep: 0.01 seconds
- Incline angle: 45 degrees
- Static friction coefficient: 1
- Dynamic friction coefficient: 1
- Rolling contacts: disabled
- Sleep threshold: 0

Under these conditions, both the expected normal force and the tangential component of gravity are approximately 14.57 N.

1. Normal contact force measurement
Simply dividing the final normalImpulse value by either the fixed timestep or the substep duration did not produce an accurate force.
The positional correction applied by the contact constraint is scaled using the number of remaining substeps. 
Does this mean that each change in the normal constraint multiplier must be converted using the remaining time at the corresponding substep?

In my tests, the following conversion produced a normal-force estimate consistent with the expected value:

normal impulse increment = change in normal Lagrange multiplier / (remaining substeps × substep duration)

This requires recording the change in normalImpulse at every substep.
 I could not reconstruct the normal force over the full physics step from the value obtained only in the final collision callback using a single time value.

2. Friction behavior
The friction issue appears to affect not only force measurement but also the motion produced by the simulation.
With one substep, the cable remained approximately in equilibrium on the 45-degree incline. 
However, with two or more substeps, the cable slid down the incline even though the timestep, friction coefficients and constraint iteration count were unchanged.

In a representative test with three substeps:

- Normal force: approximately 14.57 N
- Friction force actually applied by the simulation: approximately 10.3 N
- Expected limiting Coulomb friction: approximately 14.57 N

The friction force reconstructed from the contact data agreed with the value calculated independently from the cable’s momentum change. 
Therefore, the lower friction value was not only caused by an error in reading the collision callback. The simulation itself appeared to apply approximately 10.3 N of friction.
This suggests that the normal impulse used to calculate the Coulomb friction limit may be underestimated when multiple substeps are used.
To address this behavior, I converted the change in the normal Lagrange multiplier at each substep into a normal impulse using the corresponding remaining interval.
I then accumulated these impulses and used the accumulated value to calculate the Coulomb friction limit.

I would like to confirm the following points:

1. In Obi 6.5.4, does normalImpulse require a correction that accounts for the number of remaining substeps?
2. In the Burst backend, can the friction limit used by the simulation depend on the number of substeps?
3. Is converting each substep’s change in the normal Lagrange multiplier using its corresponding remaining interval, accumulating the resulting normal impulses, and using them for the Coulomb friction limit consistent with the intended solver implementation?
4. Has this behavior been changed in newer versions of Obi?

Thank you.]]>
I found two contact-related issues that appear to depend on the number of substeps in Obi Rope 6.5.4 using the Burst backend.

Test setup:

- Rod mass: 2.1 kg (21 particles, 0.1 kg each)
- Fixed timestep: 0.01 seconds
- Incline angle: 45 degrees
- Static friction coefficient: 1
- Dynamic friction coefficient: 1
- Rolling contacts: disabled
- Sleep threshold: 0

Under these conditions, both the expected normal force and the tangential component of gravity are approximately 14.57 N.

1. Normal contact force measurement
Simply dividing the final normalImpulse value by either the fixed timestep or the substep duration did not produce an accurate force.
The positional correction applied by the contact constraint is scaled using the number of remaining substeps. 
Does this mean that each change in the normal constraint multiplier must be converted using the remaining time at the corresponding substep?

In my tests, the following conversion produced a normal-force estimate consistent with the expected value:

normal impulse increment = change in normal Lagrange multiplier / (remaining substeps × substep duration)

This requires recording the change in normalImpulse at every substep.
 I could not reconstruct the normal force over the full physics step from the value obtained only in the final collision callback using a single time value.

2. Friction behavior
The friction issue appears to affect not only force measurement but also the motion produced by the simulation.
With one substep, the cable remained approximately in equilibrium on the 45-degree incline. 
However, with two or more substeps, the cable slid down the incline even though the timestep, friction coefficients and constraint iteration count were unchanged.

In a representative test with three substeps:

- Normal force: approximately 14.57 N
- Friction force actually applied by the simulation: approximately 10.3 N
- Expected limiting Coulomb friction: approximately 14.57 N

The friction force reconstructed from the contact data agreed with the value calculated independently from the cable’s momentum change. 
Therefore, the lower friction value was not only caused by an error in reading the collision callback. The simulation itself appeared to apply approximately 10.3 N of friction.
This suggests that the normal impulse used to calculate the Coulomb friction limit may be underestimated when multiple substeps are used.
To address this behavior, I converted the change in the normal Lagrange multiplier at each substep into a normal impulse using the corresponding remaining interval.
I then accumulated these impulses and used the accumulated value to calculate the Coulomb friction limit.

I would like to confirm the following points:

1. In Obi 6.5.4, does normalImpulse require a correction that accounts for the number of remaining substeps?
2. In the Burst backend, can the friction limit used by the simulation depend on the number of substeps?
3. Is converting each substep’s change in the normal Lagrange multiplier using its corresponding remaining interval, accumulating the resulting normal impulses, and using them for the Coulomb friction limit consistent with the intended solver implementation?
4. Has this behavior been changed in newer versions of Obi?

Thank you.]]> https://obi.virtualmethodstudio.com/forum/thread-4645.html Tue, 01 Sep 2026 07:57:49 +0200 godwinferin]]> https://obi.virtualmethodstudio.com/forum/thread-4645.html https://obi.virtualmethodstudio.com/forum/thread-4644.html Mon, 31 Aug 2026 17:28:40 +0200 goosejordan]]> https://obi.virtualmethodstudio.com/forum/thread-4644.html
Long time Obi user here. We have just released a trailer and Steampage for our game that is making extensive use of Obi. Actually, all of the game is made using Obi - I had to drop rigid body-Obi interactions to get the physics as tight as possible.



Please consider wishlisting here:
https://store.steampowered.com/app/43729...xpedition/]]>
Long time Obi user here. We have just released a trailer and Steampage for our game that is making extensive use of Obi. Actually, all of the game is made using Obi - I had to drop rigid body-Obi interactions to get the physics as tight as possible.



Please consider wishlisting here:
https://store.steampowered.com/app/43729...xpedition/]]> https://obi.virtualmethodstudio.com/forum/thread-4641.html Fri, 21 Aug 2026 21:16:43 +0200 corabelfunk]]> https://obi.virtualmethodstudio.com/forum/thread-4641.html
I tried copying the setup from the FBVS sample scene, but the simulation doesn't seem connected to the character's skeleton at all, and just falls to the ground.

How does the FBVS establish a one-way constraint from the softbody particles? Does the solver just detect that there are skeletal particles in the blueprint? Are there restrictions on how the skeleton hierarchy must be set up? I've reviewed the manual in depth but it doesn't have many details.

here's a video that shows the various issues i'm hitting, as well as the scene and blueprint setup. warning slightly NSFW: link

(i did use a skin map to mask out parts of the character, but disabled it to record the video so i could show more clearly what's going on)

I hope I can get it working; excited about the potential!]]>
I tried copying the setup from the FBVS sample scene, but the simulation doesn't seem connected to the character's skeleton at all, and just falls to the ground.

How does the FBVS establish a one-way constraint from the softbody particles? Does the solver just detect that there are skeletal particles in the blueprint? Are there restrictions on how the skeleton hierarchy must be set up? I've reviewed the manual in depth but it doesn't have many details.

here's a video that shows the various issues i'm hitting, as well as the scene and blueprint setup. warning slightly NSFW: link

(i did use a skin map to mask out parts of the character, but disabled it to record the video so i could show more clearly what's going on)

I hope I can get it working; excited about the potential!]]> https://obi.virtualmethodstudio.com/forum/thread-4640.html Wed, 19 Aug 2026 15:27:57 +0200 Jawsarn]]> https://obi.virtualmethodstudio.com/forum/thread-4640.html
Video to show issue
https://drive.google.com/drive/folders/1...x1lAva8Hga

The only way I've found to get a "completley safe" case is to set up "Use Limits" on the Solver to restrict the simulation area.

Is this a bug? It feels a bit contradictory to the "unconditionally stable" from documentation https://obi.virtualmethodstudio.com/manu...gence.html.

Thanks for input.]]>
Video to show issue
https://drive.google.com/drive/folders/1...x1lAva8Hga

The only way I've found to get a "completley safe" case is to set up "Use Limits" on the Solver to restrict the simulation area.

Is this a bug? It feels a bit contradictory to the "unconditionally stable" from documentation https://obi.virtualmethodstudio.com/manu...gence.html.

Thanks for input.]]> https://obi.virtualmethodstudio.com/forum/thread-4639.html Mon, 17 Aug 2026 10:05:40 +0200 TubbyCrumbles]]> https://obi.virtualmethodstudio.com/forum/thread-4639.html I would like to use your softbody system in a web build but I get an error:

Error building Player: Shader error in 'FluidFoamCollisions': Buffer count exceeding hard limit. No known hw supports this shader. Consider combining separate buffers into one containing struct elements. at kernel SolveDiffuseContacts (on gles3)

Is this a known issue? Is there a fix?]]> I would like to use your softbody system in a web build but I get an error:

Error building Player: Shader error in 'FluidFoamCollisions': Buffer count exceeding hard limit. No known hw supports this shader. Consider combining separate buffers into one containing struct elements. at kernel SolveDiffuseContacts (on gles3)

Is this a known issue? Is there a fix?]]> https://obi.virtualmethodstudio.com/forum/thread-4638.html Sat, 08 Aug 2026 04:34:05 +0200 isenberg]]> https://obi.virtualmethodstudio.com/forum/thread-4638.html
But when switching to Compute (GPU), the non-static object is ignored completely by the fluid. The flow speed isn't really high, maybe 4 m/s and the emitter of 0.4 m^2 is set to speed 1.5 only.

A 2nd missed collision is happening at only one of the static colliders, which isn't obviously different than the others. At least that I could fix by increasing the Obi Collider thickness and is an acceptable workaround for that one.

Only when setting thickness to 2.79 or larger on the non-static collider, it reacts correctly, but that's far too wide as the non-static object is only 1x1x2 m large. Also when adding a completely new simple Cube with RigidBody + Box Collider + Obi Collider, that new object is completely ignored by the fluid.


I suspect some dependency on the surrounding box the non-static object is located inside. Maybe Obi Solver tries to optimized too much, but how to prevent that?

Unity 6.5, Obi Fluid 7.1.1
Currently 100000 fluid particles at 2 res, but same problem with res 0.4 and only 2000.]]>
But when switching to Compute (GPU), the non-static object is ignored completely by the fluid. The flow speed isn't really high, maybe 4 m/s and the emitter of 0.4 m^2 is set to speed 1.5 only.

A 2nd missed collision is happening at only one of the static colliders, which isn't obviously different than the others. At least that I could fix by increasing the Obi Collider thickness and is an acceptable workaround for that one.

Only when setting thickness to 2.79 or larger on the non-static collider, it reacts correctly, but that's far too wide as the non-static object is only 1x1x2 m large. Also when adding a completely new simple Cube with RigidBody + Box Collider + Obi Collider, that new object is completely ignored by the fluid.


I suspect some dependency on the surrounding box the non-static object is located inside. Maybe Obi Solver tries to optimized too much, but how to prevent that?

Unity 6.5, Obi Fluid 7.1.1
Currently 100000 fluid particles at 2 res, but same problem with res 0.4 and only 2000.]]> https://obi.virtualmethodstudio.com/forum/thread-4637.html Mon, 27 Jul 2026 15:52:13 +0200 Qriva0]]> https://obi.virtualmethodstudio.com/forum/thread-4637.html This is quite annoying when commiting changes in git, so it would be great if that did not happen. Maybe hide flags could help?]]> This is quite annoying when commiting changes in git, so it would be great if that did not happen. Maybe hide flags could help?]]> https://obi.virtualmethodstudio.com/forum/thread-4636.html Mon, 27 Jul 2026 15:46:36 +0200 Qriva0]]> https://obi.virtualmethodstudio.com/forum/thread-4636.html https://jerryhsu.io/wp-content/uploads/2...t_Rods.pdf]]> https://jerryhsu.io/wp-content/uploads/2...t_Rods.pdf]]> https://obi.virtualmethodstudio.com/forum/thread-4634.html Fri, 17 Jul 2026 20:23:02 +0200 Jawsarn]]> https://obi.virtualmethodstudio.com/forum/thread-4634.html https://obi.virtualmethodstudio.com/forum/thread-4633.html Wed, 08 Jul 2026 14:34:35 +0200 OstapDev]]> https://obi.virtualmethodstudio.com/forum/thread-4633.html ObiParticleAttachment.cs, where these offsets were set.
Please add a checkbox to disable the offsets, or the ability to adjust them. 

Obi Physics Suite v7.1.1]]> ObiParticleAttachment.cs, where these offsets were set.
Please add a checkbox to disable the offsets, or the ability to adjust them. 

Obi Physics Suite v7.1.1]]> https://obi.virtualmethodstudio.com/forum/thread-4632.html Wed, 24 Jun 2026 16:16:40 +0200 Haim_MCAI]]> https://obi.virtualmethodstudio.com/forum/thread-4632.html https://obi.virtualmethodstudio.com/forum/thread-4631.html Wed, 17 Jun 2026 19:02:57 +0200 vendolis]]> https://obi.virtualmethodstudio.com/forum/thread-4631.html The game is very limited, as it is normal for a gamejam project, but still was fun to make and play: https://vendolis.itch.io/color-weave
It scored 70th of 833 overall and 20th in theme. 

It was a fun experiences esp to keep the rope steady and under tension, while not over stretching it. I kind of wish there was a "tensioner" for the rope that keeps the rope at a specific tension all the time. I wrote something that goes into that direction, but it is quite clunky.

I also wished there was more documentation on how the rope collisions are calculated, since apparently they are done around the 0-coordiantes and you can collide with them, even though collisions are turned off for the rope. I noticed that this is why the rope demo is off axis. It took me a while to understand the intricacies around this. Naturally I also would love for this to work in WebGL, but even though Burst is now available, it was too slow to work and I had not time to dive in deeper.]]> The game is very limited, as it is normal for a gamejam project, but still was fun to make and play: https://vendolis.itch.io/color-weave
It scored 70th of 833 overall and 20th in theme. 

It was a fun experiences esp to keep the rope steady and under tension, while not over stretching it. I kind of wish there was a "tensioner" for the rope that keeps the rope at a specific tension all the time. I wrote something that goes into that direction, but it is quite clunky.

I also wished there was more documentation on how the rope collisions are calculated, since apparently they are done around the 0-coordiantes and you can collide with them, even though collisions are turned off for the rope. I noticed that this is why the rope demo is off axis. It took me a while to understand the intricacies around this. Naturally I also would love for this to work in WebGL, but even though Burst is now available, it was too slow to work and I had not time to dive in deeper.]]> https://obi.virtualmethodstudio.com/forum/thread-4630.html Tue, 16 Jun 2026 20:22:55 +0200 Balou]]> https://obi.virtualmethodstudio.com/forum/thread-4630.html I've had amazing feedbacks on the rope sim and the rod loading, the way it moves with the river current. 
So yeah here is my made with Obi: Wade, with a demo available on Steam if you want to give it a try!



The rope sim runs fine on a Quest 2 (it's CPU so not a problem) and I'm still using obi 6.X. 
Tell me what you think!]]> I've had amazing feedbacks on the rope sim and the rod loading, the way it moves with the river current. 
So yeah here is my made with Obi: Wade, with a demo available on Steam if you want to give it a try!



The rope sim runs fine on a Quest 2 (it's CPU so not a problem) and I'm still using obi 6.X. 
Tell me what you think!]]> https://obi.virtualmethodstudio.com/forum/thread-4629.html Wed, 10 Jun 2026 12:40:32 +0200 Trogdor]]> https://obi.virtualmethodstudio.com/forum/thread-4629.html
So I have upgraded my design to a suture study. I have a needle with a dynamic particle attachment to an ObiRope, and then I am using a sphere as a dynamic particle attachment to anchor the rope. The sphere has an ObiCollider attached to it, so that it can't pass through the tissue.

I have two softbodies, one acting as the left tissue and the other as the right tissue. I have a static particle attachement on those connecting the particles at the bottom of the tissue to the tabletop, to keep them rigid.

I am using Unity 6.3, and Obi 7.1, and both actors are assigned the same solver.

What I would like to see is that when the rope passes through the two softbodies, and force is applied to the rope, the tissue pulls together, with the aim to have this occur when a knot is tied.

My graspers interact with the tissue and can move it around, and they can pickup the needle. I have setup that when the needle punctures the tissue it connects to the nearest traingle and attaches a gameobject for the entrance and exit points. Then, when the rope passes through the tissue, it creates pinholes so that the thread passes through the tissue. What I am struggling to do is create and attachment between the rope and the tissue to generate the tissue deformation I am expecting, or that I am going about this entirely wrong. I know there are a number of people that have created suturing demos on here, but most link back to either a DaVinci DVKR or haptic controllers, whereas I am trying to do it in the oculus. I have been trying to use this paper as an examplar, specifically fig 19.

If anyone can provide some assistance that would be wonderful.

Thanks.]]>
So I have upgraded my design to a suture study. I have a needle with a dynamic particle attachment to an ObiRope, and then I am using a sphere as a dynamic particle attachment to anchor the rope. The sphere has an ObiCollider attached to it, so that it can't pass through the tissue.

I have two softbodies, one acting as the left tissue and the other as the right tissue. I have a static particle attachement on those connecting the particles at the bottom of the tissue to the tabletop, to keep them rigid.

I am using Unity 6.3, and Obi 7.1, and both actors are assigned the same solver.

What I would like to see is that when the rope passes through the two softbodies, and force is applied to the rope, the tissue pulls together, with the aim to have this occur when a knot is tied.

My graspers interact with the tissue and can move it around, and they can pickup the needle. I have setup that when the needle punctures the tissue it connects to the nearest traingle and attaches a gameobject for the entrance and exit points. Then, when the rope passes through the tissue, it creates pinholes so that the thread passes through the tissue. What I am struggling to do is create and attachment between the rope and the tissue to generate the tissue deformation I am expecting, or that I am going about this entirely wrong. I know there are a number of people that have created suturing demos on here, but most link back to either a DaVinci DVKR or haptic controllers, whereas I am trying to do it in the oculus. I have been trying to use this paper as an examplar, specifically fig 19.

If anyone can provide some assistance that would be wonderful.

Thanks.]]>