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Fix FBX import normals to respect smoothing groups #114758

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Fix FBX import normals to respect smoothing groups #114758

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f0086ff
Fix FBX import normals to respect smoothing groups
fire Jan 8, 2026
1c2e8d4
Update modules/fbx/fbx_document.cpp
fire Jan 9, 2026
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49 changes: 45 additions & 4 deletions modules/fbx/fbx_document.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -611,9 +611,50 @@ Error FBXDocument::_parse_meshes(Ref<FBXState> p_state) {
array[Mesh::ARRAY_VERTEX] = _decode_vertex_attrib_vec3(fbx_mesh->vertex_position, indices);
}

// Normals always exist as they're generated if missing,
// see `ufbx_load_opts.generate_missing_normals`.
Vector<Vector3> normals = _decode_vertex_attrib_vec3(fbx_mesh->vertex_normal, indices);
// Generate normals respecting FBX smoothing groups
Vector<Vector3> normals;
normals.resize(vertex_num);

HashMap<Vector3, Vector3> normal_accum_smooth;
HashMap<Vector3, int> normal_count_smooth;
HashMap<Vector3, Vector3> normal_accum_faceted;
HashMap<Vector3, int> normal_count_faceted;

for (size_t face_idx = 0; face_idx < fbx_mesh->faces.count; face_idx++) {
ufbx_face face = fbx_mesh->faces.data[face_idx];

if (face.num_indices >= 3) {
Vector3 v0 = _as_vec3(fbx_mesh->vertex_position[face.index_begin]);
Vector3 v1 = _as_vec3(fbx_mesh->vertex_position[face.index_begin + 1]);
Vector3 v2 = _as_vec3(fbx_mesh->vertex_position[face.index_begin + 2]);

Vector3 face_normal = Plane(v0, v1, v2).normal;

bool is_smooth = (face_idx < fbx_mesh->face_smoothing.count) ? fbx_mesh->face_smoothing.data[face_idx] : false;
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HashMap<Vector3, Vector3> &normal_accum = is_smooth ? normal_accum_smooth : normal_accum_faceted;
HashMap<Vector3, int> &normal_count = is_smooth ? normal_count_smooth : normal_count_faceted;

normal_accum[v0] += face_normal;
normal_accum[v1] += face_normal;
normal_accum[v2] += face_normal;
normal_count[v0]++;
normal_count[v1]++;
normal_count[v2]++;
}
}

for (int i = 0; i < vertex_num; i++) {
Vector3 vertex_pos = _as_vec3(fbx_mesh->vertex_position[indices[i]]);

if (normal_count_smooth.has(vertex_pos) && normal_count_smooth[vertex_pos] > 0) {
normals.write[i] = (normal_accum_smooth[vertex_pos] / normal_count_smooth[vertex_pos]).normalized();
} else if (normal_count_faceted.has(vertex_pos) && normal_count_faceted[vertex_pos] > 0) {
normals.write[i] = (normal_accum_faceted[vertex_pos] / normal_count_faceted[vertex_pos]).normalized();
} else {
normals.write[i] = Vector3(0, 1, 0);
}
}
array[Mesh::ARRAY_NORMAL] = normals;

if (fbx_mesh->vertex_tangent.exists) {
Expand Down Expand Up @@ -2053,7 +2094,7 @@ Error FBXDocument::_parse(Ref<FBXState> p_state, const String &p_path, Ref<FileA
opts.ignore_geometry = true;
opts.ignore_embedded = true;
}
opts.generate_missing_normals = true;
opts.generate_missing_normals = false;

ThreadPoolFBX thread_pool;
thread_pool.pool = WorkerThreadPool::get_singleton();
Expand Down