Bevy 0.16 upgrade (#24)

src/utils/trail.rs

@@ -0,0 +1,63 @@
+use bevy::prelude::*;
+
+use crate::GameState;
+
+#[derive(Component)]
+pub struct Trail {
+    points: Vec<Vec3>,
+    col: LinearRgba,
+}
+
+impl Trail {
+    pub fn new(pos: Vec3, col: LinearRgba) -> Self {
+        let mut v = Vec::with_capacity(12);
+        v.push(pos);
+        Self { points: v, col }
+    }
+
+    pub fn add(&mut self, pos: Vec3) {
+        if self.points.len() >= self.points.capacity() {
+            self.points.pop();
+        }
+        self.points.insert(0, pos);
+    }
+}
+
+pub fn plugin(app: &mut App) {
+    app.add_systems(
+        FixedUpdate,
+        update_trail.run_if(in_state(GameState::Playing)),
+    );
+}
+
+fn update_trail(
+    mut query: Query<(&mut Trail, &Gizmo, &GlobalTransform, &ChildOf)>,
+    global_transform: Query<&GlobalTransform>,
+    mut gizmo_assets: ResMut<Assets<GizmoAsset>>,
+) -> Result<(), BevyError> {
+    for (mut trail, gizmo, pos, parent) in query.iter_mut() {
+        trail.add(pos.translation());
+
+        let parent_transform = global_transform.get(parent.parent())?;
+
+        let Some(gizmo) = gizmo_assets.get_mut(gizmo.handle.id()) else {
+            continue;
+        };
+
+        for window in trail.points.windows(2) {
+            let [a, b] = window else {
+                continue;
+            };
+            let a = GlobalTransform::from_translation(*a)
+                .reparented_to(parent_transform)
+                .translation;
+            let b = GlobalTransform::from_translation(*b)
+                .reparented_to(parent_transform)
+                .translation;
+
+            gizmo.line(a, b, trail.col);
+        }
+    }
+
+    Ok(())
+}