Obi Official Forum - Obi Fluid

2D URP Renderer

Fri, 02 Oct 2026 17:49:48 +0200

I'm aware 2D lightning is not supported, but I'm just trying a little transparence, without any kind of refraction or reflection with fluids over 2D sprites.

Opaque fluids are working nicely enough over sprites, but if it could only have a small transparence over sprites it would be perfect for my use case.

When I try the standard universal URP, fluids become translucid and do not take any colors, also fluids when above spirte, even being translucid, make sprites completly vanish.

I'm quite sure I'm using the correct set up, but would greatly appreciate if there is anyway to make my use case work.

Thanks!

[Obi Fluid 7] URP Fluid Renderer Feature causes UniversalRenderPipeline..ctor

Thu, 24 Sep 2026 20:47:37 +0200

Hi, my English isn't very good, so I used AI to translate and summarize this article. Thanks for understanding!

My setup
- Obi Fluid 7.x, Unity 6000.3.24f1, URP, IL2CPP, arm64, Managed Stripping = Minimal, Development build.
- Device: Samsung Galaxy S23 (SM-S9180), Adreno 740, Android 14. Repro on both Vulkan 1.3 and OpenGL ES 3.2.
- In the Editor (desktop, Compute backend) everything works perfectly (~120 fps).

Problem
On device the screen is black. Logcat shows this NullReferenceException repeating every frame:
NullReferenceException: Object reference not set to an instance of an object.
at UnityEngine.Rendering.Universal.UniversalRenderPipeline..ctor (UniversalRenderPipelineAsset asset)
at UnityEngine.Rendering.Universal.UniversalRenderPipelineAsset.CreatePipeline ()
at UnityEngine.Rendering.RenderPipelineAsset.InternalCreatePipeline ()
at UnityEngine.Rendering.RenderPipelineManager.TryPrepareRenderPipeline (...) at UnityE
The whole URP pipeline fails to be created, so nothing renders.

Key finding — it is the Obi Fluid Renderer Feature
- With the Obi Fluid Renderer Feature ENABLED on the URP renderer → the NRE above → black screen.
- With the feature DISABLED → URP renders fine (I can see the scene and the raw fluid particles), no NRE.
- Reproduced with both Compute and Burst backends.
- Reproduced with both Vulkan and OpenGL ES 3.2.
- The stack trace contains no Obi frames or line numbers (IL2CPP), just URP internals.

The simulation itself runs on device
Obi's own warning appears in logcat: "Hashtable usage should be below 50% ... Increase max surface chunks in your ObiSolver" (from Obi...), so the solver + surface mesher are running — the crash is specifically in the URP renderer-feature / pipeline construction.

Separate issue I already worked around (maybe related)
With the Compute backend I first got:
ArgumentException: The total size of the graphics buffer (150994944 bytes) exceeds the maximum buffer size. Maximum supported buffer size: 134217728 bytes (mobile's 128 MB GPU buffer cap).
I traced this to the surface mesher buffers (maxVoxels = maxSurfaceChunks * chunkRes^3). Lowering ObiSolver.maxSurfaceChunks from the default 32768 to 16384 removed that ArgumentException. But the UniversalRenderPipeline..ctor NRE (above) still remains.

Question
Why does the Obi Fluid Renderer Feature make UniversalRenderPipeline..ctor throw a NullReferenceException on this Android device, and how can I get the URP fluid renderer to work on mobile? Is there a known fix / required setting / shader change for Adreno / Unity 6 / URP 17?

Thanks!

What is the purpose of serializing solverIndices?

Thu, 10 Sep 2026 01:20:33 +0200

Hello! I've been working on a project with multiple contributors and noticed that the ObiEmitters have a serialized field called solverIndices, inherited from the ObiActor. I've noticed that it's common for the solverIndices to be re-serialized, leading to rather messy diffs.

As far as I can tell, this field seems to only be used for the runtime fluid simulation, and probably shouldn't be serialized, but I'm wondering why it might be.

Is this to survive domain reloads? In that case, there might be other ways around it, like storing the solverIndices that need to survive as part of a ScriptableObjectSingleton. Or would there be any other way to needless diffs?

Fluid tunnels through Obi Collider with Compute (GPU) backend, not with Burst (CPU)

Sat, 08 Aug 2026 04:34:05 +0200

In my simple scene of maybe 10 static box colliders with each an associated Obi Collider the fluid correctly reacts to those static colliders, in CPU and GPU backend mode. It also reacts correctly to the one non-static gravity-influences box collider + Obi Collider.

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.

Extend lifespan and stream time

Fri, 22 May 2026 01:21:57 +0200

Hello, from what I've experimented with, it's a trade off between lifespan and the stream time. For instance, if my lifespan is 5 seconds then I can only have a stream for a few seconds until it stops and I must wait while the spawned fluid despawns. Am I understanding this correctly and is there a way to keep the stream going regardless of the life span? Thank you!

Water Tunneling Through Mug When Grabbed in VR (Unity 6.3+Obi 7.1.1+XR Interaction)

Wed, 20 May 2026 15:24:18 +0200

I'm working on a VR application where players need to fill a mug with water and pour it onto trees. I'm running into an issue with the Obi fluid behaviour when the mug is grabbed.

Current Setup:
- Unity 6.3
- Obi 7.1.1
- XR Interaction Toolkit

What's Working:
- The mug fills with water correctly
- The player can grab and move the mug using XR Interaction Toolkit

The Problem:
When the player grabs the mug, the water starts tunneling through the container instead of staying inside and moving with the mug.

Video link: Tunneling issue link

Questions:
1. Is there a specific way to configure the Obi Collider or Obi Solver when using XR grabbable objects?
2. Do I need to adjust the rigidbody settings on the mug when it's grabbed?
3. Are there any known compatibility issues between Obi Fluid and XR Interaction Toolkit's grab mechanics?

Memory Leak - AccumulateTransmissionURP.shader

Mon, 20 Apr 2026 22:47:28 +0200

Im seeing millions of un-destroyed instances of materials when playtesting called "Hidden/AccumulateTransmissionURP" around 1.9kb each - possibly related to the AccumulateTransmissionURP.shader.

Frame debugger shows nothing using this shader.

Memory profiler shows:
Shortest Path To Root shows "ROOT: Material "Hidden/AccumulatedTransmissionURP"
Referenced by: empty
References TO: Shader "Hidden/AccumulatedTransmissionURP"

Oddly this bug is only apparent when testing on PC. If i test a build on android this leak does not happen.

Im unsure of how to continue diagnosing this. Anyone have any advice?

Thanks and Thank you for the great physics package!

Help with water in a bottle.

Thu, 16 Apr 2026 21:33:43 +0200

I need help with water inside a bottle. I’m using HDRP, and I’m trying to create water in a bottle. I already have my own bottle model, and I set everything up following the example from the demo scene with the bottle.
However, the water immediately explodes outward and that’s it, it doesn’t stay inside the bottle at all. The water in the demo bottle works perfectly, but in my bottle it doesn’t, even though I followed the same steps.
Maybe I’m doing something wrong? I can send my bottle model if needed. Please help.

Erro en el Script de ObiFluidRenderer

Tue, 14 Apr 2026 21:24:09 +0200

El problema es que usando Obi Fluid en Unity 6.4 (6.000.4.0f1) no puedo ejecutar ninguna escena de ejemplo esto debido a que obtengo errores de consola en un Script que pertenece a Obi Fluid

Este son los errores que muestra

buscando dentro de Obi Fluid veo que es el siguiente Script ObiFluidRenderFeature.cs. aquí no se si deba de mostrar el otro icono # que es con el que se identifican los archivos scripts ecritos en C #
[/url][url=https://postimages.org/]

si lo selecciono en el inspector se ve así

Ahora si abro el archivo para ver mejor el código fuente, vemos que no encuentra esos métodos. esos son lo que están causando el Error

Ahora si entro a la otra carpeta RemderBatches vemos que el Script se muestra con el icono que debe de llevar y no el otro icono del archivo que está mal.

al igual que en el inspector se ve claro su código, esto sin la necesidad de abrir el código para poderlo visualizar correctamente

esta es la segunda vez que cargo Obi Fluid en otra computadora (del trabajo) y me sale el mismo error que en la computadora (de la casa) donde tengo el proyecyo.

en el del trabajo intente con otro proyecto que solo tiene un cubo y un plano.

  error_consola.png (Size: 50.85 KB / Downloads: 0)

  Assets_proyecto.png (Size: 28.51 KB / Downloads: 0)

  script.png (Size: 139.08 KB / Downloads: 0)

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Trying to make obi fluids work with terrain holes

Fri, 13 Feb 2026 06:50:39 +0100

Hey guys!
Im working on a construction sim which uses Digger pro for voxel terrain and it uses terrain holes when digging downwards and puts a mesh in the place of the hole. Now the problem is fluids does not seem to recognise that there are holes and flows as if there is no hole.
I tested this with a plain scene with a new terrain and painted a hole and added an emitter on top, but it thinks there is no hole there.

Am I missing a setting somewhere or is there a workaround for this? Any leads will be appreciated.

Regards,
Abhishek Jathan

Simple Collision Debug Log

Sun, 25 Jan 2026 17:38:36 +0100

Hello,

I am able to make fluid collide with 3D objects using the Obi Colliders, but I have yet to figure out how to get any data back from the collision itself.
Even just a Debug.Log("Foo") would be enough to get me in the right direction.

Here's the code snippet in the documentation that I first started messing around with:

Code:
ObiColliderBase collider = ObiColliderWorld.GetInstance().colliderHandles[contact.bodyB].owner;

Any step-by-step instructions would be great. Thanks!

Correct way to update mesh colliders for Obi Fluids

Sat, 06 Dec 2025 11:39:10 +0100

Hello,

I'm trying to make Obi Fluids interact with Voxelica voxel engine, which generates chunk-based mesh colliders at runtime. However, as the Mesh objects are being modified on the Mesh Colliders, Obi Solver doesn't seem to pick up on the change. I tried manually forcing an update with several different methods in the Obi interfaces but had no luck so far. I also noticed that the GPU Solver and CPU Solver behaved differently, where CPU solvers was able to pick up on the changes with a specific combination of calls but GPU Solver wasn't. Sorry that I don't have the specific methods in mind at the moment, but I'm hoping that you can point me in the right direction.

Thanks!

Transparent fluid impacted by lighting intensity

Mon, 01 Dec 2025 11:37:48 +0100

Hi,

Is it possible to make a Obi transparent Fluid Surface Mesher to not be impacted by the environment lighting-> Intensity multiplier?
It lits up the fluid very bright and the objects behind it too get lit.

I have tried disabling reflection cubemap, light probe usage, reflection probe usage, disabled shadows. None of them seem to be working.

Can you please suggest a correct way to handle it? I want a completely transparent fluid just like water but currently, the fluid is significantly lit. Rendering pipeline: Unity Builtin.

Thank you.

Skinned Mesh Renderer behind transparent fluid not rendering

Mon, 27 Oct 2025 13:06:20 +0100

Hi, I have a transparent fluid in front of a skinned mesh renderer but cannot see through it: it contains blends. How can I fix this? (built in pipeline). Cannot see it when see through fluid but in absence of fluid or from other viewing angles it renders fine.
Thank you.

Built in renderer: fluid texture missing

Fri, 10 Oct 2025 10:42:26 +0200

Hi, I am using Obi Fluid 7.1 in built in pipeline. The textures come fine in scene view but not in game view. Obi Fluid Built In Renderer Feature' component is added to camera. How can i fixed this? Thanks!