From a342d79b86ed83d89377107097c68deb962d8587 Mon Sep 17 00:00:00 2001
From: Sergio Valor <jaildesigner@gmail.com>
Date: Fri, 22 May 2026 19:51:40 +0200
Subject: [PATCH] feat(starfield): mou estrelles amb la mitjana de velocitats
 de les naus

---
 source/game/scenes/game_scene.cpp | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/source/game/scenes/game_scene.cpp b/source/game/scenes/game_scene.cpp
index 6aeeb18..e0282df 100644
--- a/source/game/scenes/game_scene.cpp
+++ b/source/game/scenes/game_scene.cpp
@@ -214,9 +214,24 @@ void GameScene::stepPhysics(float delta_time) {
         bullet.postUpdate(delta_time);
     }
     trail_manager_.update(delta_time, ships_);
-    // De moment world_velocity = {0, 0} → estrelles quietes; al ser-hi l'estat
-    // del wraparound es resol normalment quan activem el moviment.
-    starfield_parallax_.update(delta_time, Vec2{.x = 0.0F, .y = 0.0F});
+    // Starfield: world_velocity = -mitjana_de_naus_actives. Si dues naus van en
+    // sentits oposats, es cancel·len → estrelles quietes (cap jugador "guanya").
+    // Si només n'hi ha una activa, segueix la seva velocitat.
+    Vec2 ship_vel_avg{.x = 0.0F, .y = 0.0F};
+    int n_active = 0;
+    for (const auto& ship : ships_) {
+        if (ship.isActive()) {
+            const Vec2 V = ship.getVelocityVector();
+            ship_vel_avg.x += V.x;
+            ship_vel_avg.y += V.y;
+            n_active++;
+        }
+    }
+    if (n_active > 0) {
+        ship_vel_avg.x /= static_cast<float>(n_active);
+        ship_vel_avg.y /= static_cast<float>(n_active);
+    }
+    starfield_parallax_.update(delta_time, Vec2{.x = -ship_vel_avg.x, .y = -ship_vel_avg.y});
     playfield_.update(delta_time);
     border_.update(delta_time);