[CR] Reign in the damage from items dropped from height, with math

src/item.cpp

@@ -204,7 +204,6 @@ static const quality_id qual_LIFT( "LIFT" );
 static const skill_id skill_cooking( "cooking" );
 static const skill_id skill_melee( "melee" );
 static const skill_id skill_survival( "survival" );
-static const skill_id skill_throw( "throw" );
 static const skill_id skill_weapon( "weapon" );
 
 static const species_id species_ROBOT( "ROBOT" );
@@ -14600,9 +14599,6 @@ bool item::on_drop( const tripoint &pos, map &m )
 
     avatar &player_character = get_avatar();
 
-    // set variable storing information of character dropping item
-    dropped_char_stats.throwing = player_character.get_skill_level( skill_throw );
-
     return type->drop_action && type->drop_action.call( &player_character, *this, pos );
 }
 

src/item.h

@@ -176,10 +176,6 @@ template<>
 struct enum_traits<iteminfo::flags> {
     static constexpr bool is_flag_enum = true;
 };
-// Currently used to store the only throwing stats of character dropping this item. Default is -1
-struct dropped_by_character_stats {
-    float throwing;
-};
 
 iteminfo vol_to_info( const std::string &type, const std::string &left,
                       const units::volume &vol, int decimal_places = 2, bool lower_is_better = true );
@@ -236,8 +232,6 @@ class item : public visitable
 
         ~item() override;
 
-        struct dropped_by_character_stats dropped_char_stats = { -1.0f };
-
         /** Return a pointer-like type that's automatically invalidated if this
          * item is destroyed or assigned-to */
         safe_reference<item> get_safe_reference();

src/map.cpp

@@ -2864,10 +2864,10 @@
     // rather than disappearing if it would be overloaded
 
     tripoint below( p );
-    int height_fallen = 0;
+    int max_height_fallen = 0;
     while( !has_floor_or_water( below ) ) {
         below.z--;
-        height_fallen++;
+        max_height_fallen++;
     }
 
     if( below == p ) {
@@ -2877,53 +2877,85 @@
     float damage_total = 0.0f;
     for( item &i : items ) {
         units::mass wt_dropped = i.weight();
-        float item_density = i.get_base_material().density();
-        float damage = 5 * to_kilogram( wt_dropped ) * height_fallen * item_density;
+
+        if( max_height_fallen <= 0 ) {
+            debugmsg( "Tried to calculate damage for falling item, but item somehow fell less than one z-level!" );
+            max_height_fallen = 1;
+        }
+        Creature *creature_below = get_creature_tracker().creature_at( below );
+        double height_fallen = max_height_fallen;
+        if( creature_below ) {
+            // Discount most of the first z-level's falling distance, depending on how big the creature is
+            // Characters (player/NPC) are normally medium, which is 0.5 or standing about 1.2m tall.
+            // This is shorter than the average adult, but it's an *okay* approximation.
+            height_fallen -= occupied_tile_fraction( creature_below->get_size() );
+        }
+        // in meters, assuming one z-level is ~2.5m.
+        const double distance_to_fall = height_fallen * 2.5;
+
+        // in meters per second (squared).
+        const double gravity_acceleration_constant = 9.8;
+
+        // in seconds.
+        double falling_time = sqrt( 2 * distance_to_fall / gravity_acceleration_constant );
+
+        // in meters per second.
+        double velocity_at_impact = gravity_acceleration_constant * falling_time;
+
+        // in joules.
+        double impact_energy = to_kilogram( wt_dropped ) * std::pow( velocity_at_impact, 2.0 ) / 2.0;
+
+        // in faces smashed (parts per hundred).
+        double damage = sqrt( impact_energy );
         damage_total += damage;
 
         add_item_or_charges( below, i );
 
         // Bash creature standing below
-        Creature *creature_below = get_creature_tracker().creature_at( below );
         if( creature_below ) {
             // creature's dodge modifier
             float dodge_mod = creature_below->dodge_roll();
-            // if item dropped by character their throwing skill modifier -1 if not dropped by a character
-            float throwing_mod = i.dropped_char_stats.throwing == -1.0f ? 0.0f : 5 *
-                                 i.dropped_char_stats.throwing;
 
-            // values calibrated so that %hit chance starts from 60% going up and down according to the two modifiers
-            float hit_mod = ( throwing_mod + 18 ) / ( dodge_mod + 15 );
+            // Most of the threat comes from the projectile going very fast before it enters a creature's vertical FOV
+            // or e.g. it fell from so high up that there was no indication of something coming down before it (possibly) hits
+            float hit_mod = velocity_at_impact / ( dodge_mod + 5 );
 
             int creature_hit_chance = rng( 0, 100 );
-            creature_hit_chance /= hit_mod * occupied_tile_fraction( creature_below->get_size() );
+            double avoid_chance = hit_mod * occupied_tile_fraction( creature_below->get_size() );
+            // We use sqrt here because it trends back towards 1. Spectacularly low hit_mod will still have SOME chance to hit while
+            // hits of >1 avoid_chance are not always going to strike the head
+            creature_hit_chance /= sqrt( avoid_chance );
+            bodypart_id hit_part;
             if( creature_hit_chance < 15 ) {
-                add_msg_if_player_sees( creature_below->pos(), _( "Falling %s hits %s in the head!" ), i.tname(),
-                                        creature_below->get_name() );
-                creature_below->deal_damage( nullptr, bodypart_id( "head" ), damage_instance( damage_bash,
-                                             damage ) );
+                hit_part = creature_below->get_random_body_part_of_type( body_part_type::type::head );
             } else if( creature_hit_chance < 30 ) {
-                add_msg_if_player_sees( creature_below->pos(), _( "Falling %s hits %s in the torso!" ), i.tname(),
-                                        creature_below->get_name() );
-                creature_below->deal_damage( nullptr, bodypart_id( "torso" ), damage_instance( damage_bash,
-                                             damage ) );
-            } else if( creature_hit_chance < 65 ) {
-                add_msg_if_player_sees( creature_below->pos(), _( "Falling %s hits %s in the left arm!" ),
-                                        i.tname(), creature_below->get_name() );
-                creature_below->deal_damage( nullptr, bodypart_id( "arm_l" ), damage_instance( damage_bash,
-                                             damage ) );
+                hit_part = creature_below->get_random_body_part_of_type( body_part_type::type::torso );
+            } else if( creature_hit_chance < 90 ) {
+                hit_part = creature_below->get_random_body_part_of_type( body_part_type::type::arm );
             } else if( creature_hit_chance < 100 ) {
-                add_msg_if_player_sees( creature_below->pos(), _( "Falling %s hits %s in the right arm!" ),
-                                        i.tname(), creature_below->get_name() );
-                creature_below->deal_damage( nullptr, bodypart_id( "arm_r" ), damage_instance( damage_bash,
-                                             damage ) );
+                hit_part = creature_below->get_random_body_part_of_type( body_part_type::type::leg );
             } else {
-                add_msg_if_player_sees( creature_below->pos(), _( "Falling %s misses the %s!" ), i.tname(),
-                                        creature_below->get_name() );
+                add_msg_if_player_sees( creature_below->pos(), _( "Falling %1$s misses %2$s!" ), i.tname(),
+                                        creature_below->disp_name() );
+            }
+            // Did we hit at all? Then run the message.
+            if( creature_hit_chance < 100 ) {
+                if( hit_part.is_valid() && !creature_below->is_monster() ) {
+                    //~First positional argument: Item name. Second: Name of a person (e.g. "Jane") or player (e.g. "you"). Third: Body part name, accusative.
+                    add_msg_if_player_sees( creature_below->pos(), _(
+                                                "Falling %1$s hits %2$s on the %3$s for %4$i damage!" ),
+                                            i.tname(), creature_below->disp_name(), hit_part->accusative, static_cast<int>( damage ) );
+                } else {
+                    add_msg_if_player_sees( creature_below->pos(), _( "Falling %1$s hits %2$s for %3$i damage!" ),
+                                            i.tname(), creature_below->disp_name(), static_cast<int>( damage ) );
+                }
+                // FIXME: Hardcoded damage type!
+                creature_below->deal_damage( nullptr, hit_part, damage_instance( damage_bash, damage ) );
             }
         }
 
         // Bash items at bottom since currently bash_items only bash glass items
+        // FIXME: Hardcoded damage type!
         int chance = static_cast<int>( 200 * i.resist( damage_bash, true ) / damage + 1 );
         if( one_in( chance ) ) {
             i.inc_damage();