From dc2824a095266b8ec4a8da89e47010e51d96ddcf Mon Sep 17 00:00:00 2001
From: Sergio Valor <jaildesigner@gmail.com>
Date: Thu, 21 May 2026 10:22:25 +0200
Subject: [PATCH] feat(collision): la bala transmet impulse mass-aware al
 enemic (Fase 2)
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- Defaults::Physics::Bullet::IMPACT_IMPULSE (50 px·s placeholder)
- detectBulletEnemy: calcula normal bullet→enemy, normalitza
  (fallback a direcció de bala o (0,-1) si estan solapats) i crida
  enemy.applyImpulse(normal * IMPACT_IMPULSE) abans de destruir.

El destruir() immediat encara zera la velocity, així que l'efecte
visual no es nota: serà visible quan la Fase 3 difereixi la mort.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 source/core/defaults/physics.hpp         |  5 +++++
 source/game/systems/collision_system.cpp | 11 +++++++++++
 2 files changed, 16 insertions(+)

diff --git a/source/core/defaults/physics.hpp b/source/core/defaults/physics.hpp
index 7a204ba..218cdba 100644
--- a/source/core/defaults/physics.hpp
+++ b/source/core/defaults/physics.hpp
@@ -10,6 +10,11 @@ namespace Defaults::Physics {
     constexpr float MAX_VELOCITY = 120.0F;   // px/s
     constexpr float FRICTION = 20.0F;        // px/s²
 
+    // Bullet — impacto físico contra enemigo (impulse mass-aware).
+    namespace Bullet {
+        constexpr float IMPACT_IMPULSE = 50.0F;  // Magnitud del impulse en la dirección bullet→enemy
+    }  // namespace Bullet
+
     // Explosions (debris physics)
     namespace Debris {
         constexpr float VELOCITAT_BASE = 80.0F;      // Velocidad inicial (px/s)
diff --git a/source/game/systems/collision_system.cpp b/source/game/systems/collision_system.cpp
index ff1f6f9..f610d4c 100644
--- a/source/game/systems/collision_system.cpp
+++ b/source/game/systems/collision_system.cpp
@@ -23,6 +23,17 @@ namespace Systems::Collision {
                 // *** COLISIÓN bullet → enemy ***
                 const Vec2& enemy_pos = enemy.getCenter();
 
+                // Empuje físico: impulse en la dirección bullet→enemy (fallback a la
+                // dirección de la bala si están exactamente solapados).
+                Vec2 normal = enemy_pos - bullet.getCenter();
+                if (normal.lengthSquared() > 0.000001F) {
+                    normal = normal.normalized();
+                } else {
+                    const Vec2 BVEL = bullet.getBody().velocity;
+                    normal = (BVEL.lengthSquared() > 0.0F) ? BVEL.normalized() : Vec2{.x = 0.0F, .y = -1.0F};
+                }
+                enemy.applyImpulse(normal * Defaults::Physics::Bullet::IMPACT_IMPULSE);
+
                 // 1. Puntos según tipo
                 int points = 0;
                 switch (enemy.getType()) {