ThreeJS mesh geometry collider in cannon.js

meshCollision.ts

// supposing "geometry" is a ThreeJS BufferGeometry - if it's a geometry, just skip this step
const geo = new Geometry().fromBufferGeometry(geometry);

const vertices = [];
const indices = [];

// "scale" is a uniform scale you may or may not have applied to your mesh as a whole.
// just set it to 1 if you don't scale the mesh.
for (const vert of geo.vertices) {
  vertices.push(vert.x * scale);
  vertices.push(vert.y * scale);
  vertices.push(vert.z * scale);
}

for (const face of geo.faces) {
  indices.push(face.a);
  indices.push(face.b);
  indices.push(face.c);
}

const collider = new Trimesh(vertices, indices);