implement retrograde motion marker

src/actor.rs

@@ -172,6 +172,13 @@ impl Default for ExperiencesGForce {
     }
 }
 
+#[derive(Component, Default)]
+pub struct MatchingVelocity {
+    pub entity: Option<Entity>,
+    pub pos: Option<DVec3>,
+    pub v: DVec3,
+}
+
 #[derive(Component, Default)]
 pub struct WantsAcceleration {
     pub direction: DVec3,

src/cmd.rs

@@ -1513,6 +1513,7 @@ fn spawn_entities(
             actor.insert(actor::ExperiencesAtmosphere);
         }
         if state.is_player || state.is_vehicle {
+            actor.insert(MatchingVelocity::default());
             // previously used to apply mouse movement to actor rotation, but currently unused
             actor.insert(ExternalTorque::ZERO.with_persistence(false));
         }

src/hud.rs

@@ -102,6 +102,11 @@ impl Plugin for HudPlugin {
                     .after(PhysicsSet::Sync)
                     .after(camera::apply_input_to_player)
                     .before(TransformSystem::TransformPropagate),
+                update_motion_marker
+                    .run_if(game_running)
+                    .after(PhysicsSet::Sync)
+                    .after(camera::apply_input_to_player)
+                    .before(TransformSystem::TransformPropagate),
             ),
         );
         app.insert_resource(Log {
@@ -156,6 +161,8 @@ pub struct ToggleableHudMapElement;
 #[derive(Component)]
 struct Selectagon;
 #[derive(Component)]
+struct MarkerMotionRetrograde;
+#[derive(Component)]
 struct PlayerAvatar;
 #[derive(Component)]
 pub struct IsTargeted;
@@ -798,6 +805,23 @@ pub fn setup(
     ));
     load_asset("selectagon", &mut entitycmd, &*asset_server);
 
+    // Retrograde Motion Marker
+    let mut entitycmd = commands.spawn((
+        MarkerMotionRetrograde,
+        NotShadowCaster,
+        NotShadowReceiver,
+        IsClickable {
+            name: Some("Retrograde Motion Marker".to_string()),
+            ..default()
+        },
+        SpatialBundle {
+            visibility: Visibility::Hidden,
+            transform: Transform::from_scale(Vec3::splat(0.05)),
+            ..default()
+        },
+    ));
+    load_asset("marker_motion_retrograde", &mut entitycmd, &*asset_server);
+
     ew_updateoverlays.send(UpdateOverlayVisibility);
 }
 
@@ -1028,7 +1052,6 @@ fn update_hud(
                         target_multiple = true;
                         target = None;
                     } else {
-                        target_error = true;
                         target = None;
                     }
                     if let Some(target_pos) = target {
@@ -1313,6 +1336,33 @@ fn update_target_selectagon(
     }
 }
 
+fn update_motion_marker(
+    settings: Res<Settings>,
+    q_player: Query<(&Transform, &LinearVelocity, &MatchingVelocity), With<actor::PlayerCamera>>,
+    mut q_retrograde: Query<
+        (&mut Transform, &mut Visibility),
+        (With<MarkerMotionRetrograde>, Without<actor::PlayerCamera>),
+    >,
+) {
+    if let Ok((mut trans, mut vis)) = q_retrograde.get_single_mut() {
+        if settings.hud_active && !settings.third_person {
+            if let Ok((player_trans, player_v, player_mv)) = q_player.get_single() {
+                let dv = player_v.0 - player_mv.v;
+                if dv.length() > 1.0 {
+                    *vis = Visibility::Inherited;
+                    trans.translation =
+                        player_trans.translation - (dv.as_vec3().normalize() * 2.0);
+                    trans.look_at(player_trans.translation, player_trans.up());
+                } else {
+                    *vis = Visibility::Hidden;
+                }
+            }
+        } else {
+            *vis = Visibility::Hidden;
+        }
+    }
+}
+
 fn update_ar_overlays(
     q_owners: Query<
         (Entity, &Transform, &Visibility),

src/load.rs

@@ -73,6 +73,7 @@ pub fn asset_name_to_path(name: &str) -> &'static str {
         "marker_planets" => "models/marker_planets.glb#Scene0",
         "marker_player" => "models/marker_player.glb#Scene0",
         "marker_race" => "models/marker_race.glb#Scene0",
+        "marker_motion_retrograde" => "models/marker_motion_retrograde.glb#Scene0",
         "point_of_interest" => "models/point_of_interest.glb#Scene0",
         "metis" => "models/metis.gltf#Scene0",
         "thebe" => "models/thebe.gltf#Scene0",

src/main.rs

@@ -34,6 +34,7 @@ pub mod prelude {
     pub use crate::{
         actor, audio, camera, chat, cmd, common, game, hud, load, menu, nature, var, visual, world,
     };
+    pub use actor::MatchingVelocity;
     pub use game::Cycle::Next;
     pub use game::Turn::Toggle;
     pub use game::{GameEvent, Turn};