diff --git a/src/model_physics.rs b/src/model_physics.rs
index 3c15c73..4a0595a 100644
--- a/src/model_physics.rs
+++ b/src/model_physics.rs
@@ -284,6 +284,10 @@ impl From<&model::Mesh> for PhysicsMesh{
 	fn from(mesh:&model::Mesh)->Self{
 		assert!(mesh.unique_pos.len()!=0,"Mesh cannot have 0 vertices");
 		let verts=mesh.unique_pos.iter().copied().map(Vert).collect();
+		//TODO: fix submeshes
+		//flat map mesh.physics_groups[$1].groups.polys()[$2] as face_id
+		//lower face_id points to upper face_id
+		//the same face is not allowed to be in multiple polygon groups
 		let mut faces=Vec::new();
 		let mut face_id_from_face=HashMap::new();
 		let mut mesh_topologies:Vec<PhysicsMeshTopology>=mesh.physics_groups.iter().map(|physics_group|{