// undine docs
Domain
The domain is the spatial region where the fluid simulation takes place.
In practice, it defines the simulation space that emitters, colliders, solver grids, and final mesh generation depend on.
Role of the Domain
The domain is part of the very first stage of the workflow, because scene configuration starts by defining where the liquid simulation will happen.
A clear domain definition gives context to emitters, colliders, solver resolution, density fields, boundary handling, and mesh extraction.
What the domain controls
- The spatial bounds where particles are simulated.
- The area where emitter particles are valid.
- The coordinate space for collider interaction.
- The grid region used by pressure, density, and surface reconstruction stages.
- The practical memory and performance cost of a given grid resolution.
Domain setup in the Objects tab
Select the intended bounds object in Blender, then press Tag Domain in the Objects tab.
The Domain field should update to the selected object name, and Tagged in Scene should report at least one domain.
| Check | Expected result | Why it matters |
|---|---|---|
| Domain field | Shows the intended domain object. | The solver needs a known simulation region before it can interpret emitters and colliders. |
| Tagged in Scene: Domain | Reports the domain count. | A zero count means the scene has not been prepared for simulation. |
| Emitter positions | Emitters sit inside or intersect the domain. | Particles outside the usable simulation region may be ignored or behave unexpectedly. |
| Collider positions | Colliders that should affect liquid intersect the domain region. | Collider data outside the active domain does not help the visible solve. |
Resolution and cost
Domain size and Grid Resolution work together. A larger domain at the same grid resolution gives less detail per meter, while a smaller domain concentrates detail and can reduce memory use.
The Sim Params tab exposes a host pin estimate and memory-related options because high-resolution domains can become expensive quickly.
Scale & Resolution System
Undine includes a scale-aware resolution system that separates voxel size from domain size. This makes it possible to control whether scaling the domain means more detail or the same visual motion in a smaller space.
Two independent controls give you full control:
- Resolution Mode — Choose between Relative Grid Resolution (legacy behavior) or Fixed Voxels Per Meter (stable physical resolution).
- Scale Behavior — Choose between Auto (pipeline-managed scale policy), Physical Scale (real-world values), or Cinematic Scale Lock (preserves visual look after scaling).
The Scale & Resolution controls live on the Domain object under Undine Domain > Scale & Resolution.
Where it fits in the pipeline
Scene Configuration is the first step of a typical Undine simulation. The user defines the simulation domain and then configures emitters and colliders inside that space.
Related pages
- Simulation for solver behavior inside the domain
- Emitters for particle generation
- Colliders for interaction with scene objects