common: model: remove empty vertex lists in MeshBuilder::build

lib/common/src/model.rs

@@ -144,10 +144,38 @@ impl MeshBuilder{
 	}
 	pub fn build(
 		self,
-		polygon_groups:Vec<PolygonGroup>,
-		graphics_groups:Vec<IndexedGraphicsGroup>,
-		physics_groups:Vec<IndexedPhysicsGroup>,
+		mut polygon_groups:Vec<PolygonGroup>,
+		mut graphics_groups:Vec<IndexedGraphicsGroup>,
+		mut physics_groups:Vec<IndexedPhysicsGroup>,
 	)->Mesh{
+		let mut id=0;
+		let mut map=Vec::new();
+		polygon_groups.retain(|group|{
+			let keep=match group{
+				PolygonGroup::PolygonList(polygon_list)=>!polygon_list.0.is_empty(),
+			};
+			if keep{
+				map.push(Some(PolygonGroupId::new(id)));
+				id+=1;
+			}else{
+				map.push(None);
+			}
+			!keep
+		});
+		for group in &mut graphics_groups{
+			// drop empty groups
+			group.groups.retain(|polygon_group_id|map[polygon_group_id.get() as usize].is_some());
+			for polygon_group_id in &mut group.groups{
+				*polygon_group_id=map[polygon_group_id.get() as usize].unwrap();
+			}
+		}
+		for group in &mut physics_groups{
+			// drop empty groups
+			group.groups.retain(|polygon_group_id|map[polygon_group_id.get() as usize].is_some());
+			for polygon_group_id in &mut group.groups{
+				*polygon_group_id=map[polygon_group_id.get() as usize].unwrap();
+			}
+		}
 		let MeshBuilder{
 			unique_pos,
 			unique_normal,