Implement ice physics for BadGuy enemies (#3365)

* Implement ice physics for BadGuy enemies

Add ice slipping mechanics similar to player physics:
- Add ice state tracking (m_on_ice, m_ice_this_frame)
- Detect ice tiles in collision_tile()
- Apply reduced friction on ice surfaces
- Reset ice state each frame with proper management

Closes #733

* Implement proper ice physics for BadGuy enemies

Apply identical ice physics behavior to enemies as used by the player:
- BadGuys now use same ice friction multiplier (0.1f) as Tux
- WalkingBadguys apply ice acceleration reduction during direction changes
- Remove artificial velocity threshold that prevented natural ice sliding
- Enemies now exhibit realistic ice sliding and momentum like the player

This ensures consistent ice physics behavior across all game entities,
providing the expected slippery surface effects for enemy movement.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

* Fix French comments to English in badguy ice physics

---------

Co-authored-by: Claude <[email protected]>

Author: PhilippeDataScienc

src/badguy/badguy.cpp

@@ -47,6 +47,10 @@ static const float FADEOUT_TIME = 0.2f;
 static const float X_OFFSCREEN_DISTANCE = 1280;
 static const float Y_OFFSCREEN_DISTANCE = 800;
 
+/** Ice physics constants (identical to player ice physics) */
+static const float BADGUY_ICE_FRICTION_MULTIPLIER = 0.1f;   // Same as player
+static const float BADGUY_ICE_ACCELERATION_MULTIPLIER = 0.25f; // Same as player
+
 BadGuy::BadGuy(const Vector& pos, const std::string& sprite_name, int layer,
                const std::string& burn_light_sprite_name, const std::string& ice_sprite_name,
                const std::string& fire_sprite_name) :
@@ -67,6 +71,8 @@ BadGuy::BadGuy(const Vector& pos, Direction direction, const std::string& sprite
   m_frozen(false),
   m_ignited(false),
   m_in_water(false),
+  m_on_ice(false),
+  m_ice_this_frame(false),
   m_dead_script(),
   m_melting_time(0),
   m_burn_light_sprite(SpriteManager::current()->create(burn_light_sprite_name)),
@@ -122,6 +128,8 @@ BadGuy::BadGuy(const ReaderMapping& reader, const std::string& sprite_name,
   m_frozen(false),
   m_ignited(false),
   m_in_water(false),
+  m_on_ice(false),
+  m_ice_this_frame(false),
   m_dead_script(),
   m_melting_time(0),
   m_burn_light_sprite(SpriteManager::current()->create(burn_light_sprite_name)),
@@ -456,6 +464,12 @@ BadGuy::get_allowed_directions() const
 void
 BadGuy::active_update(float dt_sec)
 {
+  // Manage ice state each frame
+  if (!m_ice_this_frame && on_ground()) {
+    m_on_ice = false;
+  }
+  m_ice_this_frame = false;
+
   if (!is_grabbed())
   {
     if (is_in_water() && m_water_affected)
@@ -472,6 +486,9 @@ BadGuy::active_update(float dt_sec)
     }
   }
 
+  // Apply ice physics if on ice
+  apply_ice_physics();
+
   if (m_frozen) {
     m_sprite->stop_animation();
   }
@@ -494,6 +511,11 @@ BadGuy::collision_tile(uint32_t tile_attributes)
     SoundManager::current()->play("sounds/splash.ogg", get_pos());
   }
 
+  if (tile_attributes & Tile::ICE) {
+    m_ice_this_frame = true;
+    m_on_ice = true;
+  }
+
   if (tile_attributes & Tile::HURTS && is_hurtable())
   {
     Rectf hurtbox = get_bbox().grown(-6.f);
@@ -729,6 +751,23 @@ BadGuy::collision_bullet(Bullet& bullet, const CollisionHit& hit)
   }
 }
 
+void
+BadGuy::apply_ice_physics()
+{
+  if (!m_on_ice || !on_ground()) return;
+  
+  float velx = m_physic.get_velocity_x();
+  // No artificial velocity threshold - let natural physics handle sliding
+  
+  // Use same friction base as player (WALK_ACCELERATION_X = 300)
+  float friction = 300.0f * BADGUY_ICE_FRICTION_MULTIPLIER; // Base friction value
+  if (velx < 0) {
+    m_physic.set_acceleration_x(friction);
+  } else if (velx > 0) {
+    m_physic.set_acceleration_x(-friction);
+  }
+}
+
 void
 BadGuy::kill_squished(GameObject& object)
 {

src/badguy/badguy.hpp

@@ -255,6 +255,9 @@ class BadGuy : public MovingSprite,
       collision_solid. */
   bool on_ground() const;
 
+  /** Apply ice physics to reduce friction when on ice */
+  void apply_ice_physics();
+
   /** Returns floor normal stored the last time when
       update_on_ground_flag was called and we touched something solid
       from above. */
@@ -296,6 +299,8 @@ class BadGuy : public MovingSprite,
   bool m_frozen;
   bool m_ignited; /**< true if this badguy is currently on fire */
   bool m_in_water; /** < true if the badguy is currently in water */
+  bool m_on_ice; /**< true if the badguy is currently on ice */
+  bool m_ice_this_frame; /**< true if the badguy touched ice this frame */
 
   std::string m_dead_script; /**< script to execute when badguy is killed */
 

src/badguy/walking_badguy.cpp

@@ -20,6 +20,9 @@
 
 #include "sprite/sprite.hpp"
 
+// Ice physics constant (identical to player ice physics)
+static const float BADGUY_ICE_ACCELERATION_MULTIPLIER = 0.25f;
+
 WalkingBadguy::WalkingBadguy(const Vector& pos,
                              const std::string& sprite_name_,
                              const std::string& walk_left_action_,
@@ -145,15 +148,17 @@ WalkingBadguy::active_update(float dt_sec, float dest_x_velocity, float modifier
   {
     /* acceleration == walk-speed => it will take one second to get from zero
      * to full speed. */
-    m_physic.set_acceleration_x (dest_x_velocity * modifier);
+    float ice_multiplier = (m_on_ice && on_ground()) ? BADGUY_ICE_ACCELERATION_MULTIPLIER : 1.0f;
+    m_physic.set_acceleration_x (dest_x_velocity * modifier * ice_multiplier);
   }
   /* Check if we're going too fast */
   else if (((dest_x_velocity <= 0.0f) && (current_x_velocity < dest_x_velocity)) ||
            ((dest_x_velocity > 0.0f) && (current_x_velocity > dest_x_velocity)))
   {
     /* acceleration == walk-speed => it will take one second to get twice the
      * speed to normal speed. */
-    m_physic.set_acceleration_x ((-1.f) * dest_x_velocity);
+    float ice_multiplier = (m_on_ice && on_ground()) ? BADGUY_ICE_ACCELERATION_MULTIPLIER : 1.0f;
+    m_physic.set_acceleration_x ((-1.f) * dest_x_velocity * ice_multiplier);
   }
   else
   {