// undine docs

Meshing

Meshing is the process of converting simulated particles into a renderable surface mesh.

Undine includes a dedicated Meshify pipeline designed to generate smooth fluid surfaces suitable for rendering.

Relationship Between Particles and Surface

The simulated fluid in Undine is represented internally as a collection of particles.

These particles store the physical state of the fluid, including properties such as position, velocity, and other solver-specific quantities.

Particles themselves are not directly renderable as a fluid surface. To produce a visual liquid surface suitable for rendering, particle data must be converted into a mesh representation.

Basic Concepts Review how particles are represented inside the simulation.

Surface Reconstruction

This process is known as surface reconstruction or meshing.

The meshing pipeline transforms the particle distribution into a continuous surface that approximates the shape of the simulated liquid.

What affects reconstruction quality

Particle density
Reconstruction parameters
Smoothing techniques applied during mesh generation

Meshing pipeline diagram

Particle data is progressively transformed into a renderable fluid surface.

graph TD
    Particle["Particle Data"]
    Density["Density Field Construction"]
    Surface["Surface Extraction"]
    Process["Mesh Processing"]
    Final["Final Surface Mesh"]

    Particle --> Density
    Density --> Surface
    Surface --> Process
    Process --> Final

Workflow See where surface reconstruction sits in the full pipeline.

Meshify presets and base controls

Selecting a Meshify preset fills the visible Meshify values. Live presets (live_sculpt / live_fast / live_balanced / live_high) target Streamflow's Mesh Every Frame mode and run during interactive playback. Final presets (final_production / final_hero / final_ultra) target offline runs and force the DENSITY_MC scalar route with full anisotropy.

The base controls define the density field and the extraction threshold before smoothing, filtering, or remeshing are applied.

Actions Meshify can be launched from the Actions tab after playback frames exist.

Control	Purpose	Practical effect
Preset	Loads a coherent group of Meshify settings.	Use lower presets for iteration and final presets for production output.
Voxel Size	Controls the voxel resolution of the reconstruction field.	Smaller values increase detail and memory cost.
Influence Radius	Controls how far each particle contributes to the surface field.	Larger values make smoother, fuller surfaces; smaller values preserve sharper particle detail.
Iso Value	Sets the threshold used to extract the surface.	Adjust when the mesh appears too inflated, too shrunken, or disconnected.

Quality controls

Quality controls tune the shape and density of the generated mesh after the surface field is built.

Control	Purpose	Guidance
Smoothing Iterations	Repeats smoothing over the extracted mesh.	Higher values reduce noise but can remove fine detail.
Smoothing Factor	Controls smoothing strength per iteration.	Use modest values when preserving sharp splashes or thin sheets.
Taubin Iterations	Applies Taubin smoothing passes.	Useful for smoothing while reducing shrinkage compared with simple smoothing.
Decimate Target	Controls mesh reduction target.	Lower values reduce geometry; a value near 1.0 keeps more detail.
Anisotropy Strength	Shapes reconstruction using directional particle information.	Increase when motion-aligned detail should be preserved.

Pipeline and backend

The Pipeline section controls the route from simulation cache to mesh extraction. Two scalar routes exist: VDB-SDF (particlesToLevelSet → volumeToMesh, fast, isotropic) and DENSITY_MC (anisotropic kernel, covariance-matrix shape, slower but fluid-shaped).

Anisotropy only fires on DENSITY_MC. If the surface looks like marbles instead of sheets, the run was on the VDB route — pick a final preset (final_hero / final_ultra) which forces DENSITY_MC, or set the route explicitly.

Control	Purpose	Notes
Scalar Route	Chooses the scalar field build route, such as VDB SDF -> VolumeToMesh.	Defines the high-level surface extraction path.
Extractor	Chooses the mesh extraction algorithm.	Dual Contouring can preserve sharper structural detail than some smoother extractors.
Adaptive Octree	Enables adaptive spatial refinement.	Useful for reducing work in empty or simple regions.
Leaf Size	Controls the smallest octree block size.	Lower values allow finer adaptation.
Max Depth	Caps octree depth.	Higher depth can increase detail and cost.
Backend Policy	Chooses backend behavior.	Strict GPU requires the GPU path instead of silently choosing a broad fallback.
Auto Async	Allows asynchronous mesh work.	Keeps long mesh operations from blocking more than necessary.
Force Smooth CUDA	Forces a smoother CUDA path where available.	Use when the GPU backend is producing the preferred result for the current setup.

Temporal stabilization and density filtering

Temporal controls reduce flicker across frames by aligning or blending the reconstruction field over time.

Density Field Filter applies additional smoothing to the density field before extraction.

Control	Purpose	When to adjust
Temporal Grid Snap	Aligns the reconstruction grid across frames.	Use to reduce frame-to-frame shimmer.
Temporal SDF Blend	Blends signed-distance field history.	Higher values can stabilize surfaces but may smooth fast-changing details.
Density Filter Passes	Number of density filter passes.	Increase when the surface is noisy.
Density Filter Strength	Strength of density filtering.	Increase gradually to avoid over-softening the mesh.

Smoothing, VDB, and SDF filtering

Expert overrides expose the detailed stages used to build and clean the surface field.

These settings are most useful after a good preset has already produced a nearly acceptable mesh.

Group	Visible controls	Purpose
Smoothing / Taubin	Mode, Taubin Iterations, Taubin Lambda, Taubin Mu, Lock Boundary	Controls advanced mesh smoothing and boundary preservation.
VDB Scene	SDF Build, Half Width, Particle Radius Scale, Trail dt Scale	Controls how particles and trails contribute to the VDB signed-distance field.
SDF Filtering / Morphology	Filter, Filter Iterations, Filter Width, Postprocess, Offset, Open, Close, Renormalize	Filters, offsets, opens, closes, and renormalizes the field before or after extraction.

Remesh and anisotropy

Remesh controls can regularize the mesh, while anisotropy controls use directional information to make the surface follow the motion and local particle shape more closely.

Anisotropy backends: COVARIANCE_MATRIX (rank-1 + neighbor covariance, the most accurate) and AUTO (covariance with velocity-CPU fallback when neighborhood build fails). Strength controls how strongly per-particle ellipsoids elongate along velocity — small values (0.5–1.0) keep splashes natural, larger values (1.2+) emphasize jet shape.

Group	Visible controls	Purpose
Remesh / Feature Locking	Remesh Iterations, Target Edge Scale, Relax Factor, Flip Edges, Lock Features, Feature Angle	Improves mesh element quality while preserving important features when locking is active.
Anisotropy Shape	Shape Smoothing, Shape Tau	Smooths directional shape information over time.
Adaptive Radius	Adaptive Radius, Radius Scale, Radius Min, Radius Max	Changes reconstruction radius based on local behavior while keeping it inside a controlled range.
Legacy Density Anisotropy Detail	Backend, TD Velocity Smoothing, Tau, Speed Epsilon, History TTL, GC Period	Legacy or compatibility controls for anisotropy history and cleanup.

Meshify actions and cache state

The Debug / Diagnostics area shows Meshify cache status and exposes Create Fluid Mesh.

The cache readout can report how many frames are available and how many are missing. Missing frames explain fallbacks or incomplete mesh output.

Debug See diagnostics and cache interpretation.

Readout or control	Meaning	Use
Meshify cache	Reports cached frame count and missing frames.	Check before expecting a complete mesh sequence.
Create Fluid Mesh	Starts mesh creation from the current cache and Meshify settings.	Use after simulation frames exist and presets are configured.
Done: frames / fallback	Reports completion status and whether fallback behavior was used.	Use as a signal to inspect backend policy, missing frames, and mesh settings.

Motion blur with no extra steps

Every time Meshify exports the fluid to Alembic, it automatically writes the per-vertex .velocities attribute — a velocity vector consistent with the solver, not an approximation derived by the renderer.

Cycles, EEVEE, Karma, RenderMan, or any renderer that respects the Alembic standard reads it as native motion blur input. No need to export separate caches, cook auxiliary passes, or wire a Geometry Nodes Vector Attribute setup.

The production flow collapses to: mesh it, open the renderer, enable Motion Blur. The blur is already physically aligned with the simulation you cached.

How to enable it

Run MESHIFY SIMULATION with the preset of your choice — Alembic is the default export.
In the render properties, enable Motion Blur (Render Properties → Motion Blur).
If your renderer expects a non-standard attribute name (rare), point it at velocities.

Why it matters

Motion blur derived from transforms or from frame-to-frame deltas introduces artifacts on geometry that changes topology every frame — which is exactly what a fluid mesh does.

Per-vertex .velocities solves that: every vertex of the mesh carries its own Lagrangian velocity, taken from the solver's field. The blur the renderer produces is the blur the actual fluid would have.

Workflow Where Alembic export fits into the rest of the pipeline.

Meshing in context

Surface reconstruction is one of the pipeline's endpoints, but it's not an isolated step: mesh quality depends on the simulation feeding it, and in turn shapes whatever renderer consumes it.

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