File I/O¶

MMG's file readers/writers are compiled in and operate on an in-memory filesystem (Emscripten MEMFS) exposed as mmg.FS. Nothing touches the real disk: you copy bytes in, let MMG read them, and copy results out.

Formats¶

Format	Load	Save
Medit ASCII/binary (`.mesh`/`.meshb`)	`loadMesh`	`saveMesh`
Medit solutions (`.sol`/`.solb`)	`loadSol`, `loadAllSols`	`saveSol`, `saveAllSols`
Gmsh (`.msh`, v2)	`loadMshMesh`, `loadMshMesh_and_allData`	`saveMshMesh`, `saveMshMesh_and_allData`
Format auto-detection	`loadGenericMesh`	`saveGenericMesh`
Tetgen (`.node`/`.ele`...)	—	`saveTetgenMesh` (mmg3d)
VTK (`.vtk`/`.vtu`/`.vtp`)	declared, fails at runtime	declared, fails at runtime

VTK entry points

The loadVtkMesh/saveVtuMesh/... functions exist in the API (they are part of MMG's headers) but the WASM build compiles MMG without VTK, so they return an error at runtime. Use Medit or Gmsh formats instead.

Round trip example¶

const mmg = await initialize();
const { mmg3d, FS } = mmg;

// bring a mesh file into the sandbox (Node example)
import { readFile } from 'node:fs/promises';
FS.writeFile('/input.mesh', await readFile('input.mesh'));

const h = mmg3d.init();
mmg3d.loadMesh(h.mesh, '/input.mesh');
mmg3d.setDparameter(h.mesh, h.met, mmg3d.DPARAM_hausd, 0.01);
mmg3d.remesh(h.mesh, h.met);
mmg3d.saveMesh(h.mesh, '/output.mesh');
mmg3d.free(h);

const bytes = FS.readFile('/output.mesh');            // Uint8Array
const text = FS.readFile('/output.mesh', { encoding: 'utf8' });

In the browser, fetch the input instead:

const buf = new Uint8Array(await (await fetch('part.mesh')).arrayBuffer());
FS.writeFile('/part.mesh', buf);

Solutions¶

mmg3d.loadSol(h.mesh, h.met, '/metric.sol');   // metric / level-set values
mmg3d.saveSol(h.mesh, h.met, '/out.sol');

loadAllSols/saveAllSols handle multi-field .sol files together with setSolsAtVerticesSize/getSolsAtVerticesSize and the *ithSol_inSolsAtVertices accessors.

File names inside the structures¶

setInputMeshName/setOutputMeshName (and the Sol variants) store default file names in the structures; saveMesh(mesh, null) then uses the stored name. Passing an explicit path is usually simpler.

MEMFS notes¶

Paths are POSIX-style, rooted at /; FS.mkdir('/data') creates directories.
Contents live in WASM memory: delete big files with FS.unlink when done.
MEMFS is per-initialize() call and vanishes with the instance.