MMG Remesh & Level-set

The Mesh Modification section runs the MMG remeshers in-process via the @loumalouomega/mmg-wasm WebAssembly build (MMG v5.8.0) — no native binaries. Both operations join the operation history like any other edit.

WARNING

MMG is tetrahedron / triangle based. Hexahedral, pyramid, and quadratic meshes are rejected with a message. Use it on tet volumes or triangulated surfaces.

Module auto-selection

The right MMG module is chosen automatically from the mesh (and can be overridden under Advanced):

Mesh	Module
Tetrahedral volume (+ pass-through prisms, boundary triangles / quads / edges)	mmg3d
Non-planar triangulated surface	mmgs
Planar triangulation (+ quads)	mmg2d

Remesh

Three modes:

• size × factor — the one-knob refine / coarsen: each node gets a metric equal to its current local edge size times your factor (0.5 → twice as fine, 2 → twice as coarse).
• uniform — remesh to a constant target edge size (hsiz).
• optimize — size-preserving quality optimization (IPARAM_optim).

The Advanced sub-form exposes MMG's tuning surface:

• hmin / hmax — size bounds.
• hausd — Hausdorff distance controlling geometry approximation. Defaults to 0.5 % of the bounding-box diagonal (MMG's own default is the absolute value 0.01, which explodes on large domains).
• hgrad — size gradation (how fast element size may change).
• angle detection threshold in degrees (≤ 0 disables ridge detection).
• keep surface (nosurf) / no insert / no swap / no move toggles.

Level-set split

Level-set split (MMG) discretizes an isovalue of any nodal field as an explicit, conforming boundary. Pick the field (vector fields use their magnitude) and the isovalue; the mesh is split into MMG_Domain_Inside / MMG_Domain_Outside blocks separated by an MMG_Interface layer.

Each created region is also generated as a SubModelPart of the same name, so the domains and the interface appear in the outline's SubModelParts section — ready to be isolated, exported, or deleted, and written as real Begin SubModelPart blocks on save. On volume meshes, surface only (IPARAM_isosurf) splits just the boundary surfaces. Its own Advanced sub-form exposes the same hmin / hmax / hausd / hgrad size controls and module override.

What survives a remesh

• Element / condition / geometry blocks keep their names — every cell is tagged with an MMG reference encoding its block + SubModelPart membership, and the output is regrouped from those references.
• SubModelParts are rebuilt the same way (their node lists become the connectivity closure of their surviving cells).
• Nodal / elemental data cannot follow a remesh — the fields are dropped and the result message says so. Node and entity ids are freshly renumbered.

Live progress & cancellation

MMG runs in a worker thread, so the editor never freezes during a long remesh. Press the form's ▶ play button to start: an inline loading bar just below streams MMG's live output — the analysis and meshing phases, gradation, and split / collapse / swap counters — while the play button turns into a ■ stop button that cancels the run immediately, leaving the mesh unchanged.

Because the operations are deterministic, remesh steps saved in a JSON recipe re-run MMG exactly when the recipe is replayed, and undo is instant (the result is snapshotted).