implement "relativeto" command

src/commands.rs

@@ -6,6 +6,7 @@ use bevy::math::DVec3;
 use crate::{actor, nature, world};
 use regex::Regex;
 use std::f32::consts::PI;
+use std::collections::HashMap;
 
 pub struct CommandsPlugin;
 impl Plugin for CommandsPlugin {
@@ -163,6 +164,7 @@ pub fn load_defs(
     let mut state = ParserState::default();
     let mut command;
     let mut parameters;
+    let mut id2pos: HashMap<String, DVec3> = HashMap::new();
 
     let mut line_nr = -1;
     while let Some(line) = lines.next() {
@@ -214,11 +216,23 @@ pub fn load_defs(
                     continue;
                 }
             }
+            ["relativeto", id] => {
+                match id2pos.get(&id.to_string()) {
+                    Some(pos) => {
+                        state.pos += *pos;
+                    }
+                    None => {
+                        error!("Specified `relativeto` command but could not find id `{id}`");
+                        continue;
+                    }
+                }
+            }
             ["sphere", "yes"] => {
                 state.is_sphere = true;
             }
             ["id", id] => {
                 state.id = id.to_string();
+                id2pos.insert(state.id.clone(), state.pos.clone());
             }
             ["alive", "yes"] => {
                 state.is_alive = true;