Use breathability to measure protection against liquid ammo

src/creature.cpp

@@ -1201,6 +1201,19 @@ void Creature::deal_projectile_attack( Creature *source, dealt_projectile_attack
         }
     }
 
+    if( attack.proj.proj_effects.count( "LIQUID" ) > 0 ) {
+        if( Character *char_target = as_character() ) {
+            // clothing_wetness_mult returns the effective permeability of the armor on bp_hit
+            // as a float between 0 and 1
+            // 0 permeability means no liquid touches the skin and the damage is negated
+            // 1 permeability means all liquid touches the skin and no damage is negated
+            float permeability = char_target->worn.clothing_wetness_mult( hit_selection.bp_hit );
+            permeability = std::clamp( permeability, 0.0f, 1.0f );
+
+            impact.mult_damage( permeability );
+        }
+    }
+
     dealt_dam = deal_damage( source, hit_selection.bp_hit, impact, wp_attack_copy );
     // Force damage instance to match the selected body point
     dealt_dam.bp_hit = hit_selection.bp_hit;

src/ranged.cpp

@@ -2053,6 +2053,10 @@ static projectile make_gun_projectile( const item &gun )
     proj.range = gun.gun_range();
     proj.proj_effects = gun.ammo_effects();
 
+    if( gun.ammo_data()->phase == phase_id::LIQUID ) {
+        proj.proj_effects.insert( "LIQUID" );
+    }
+
     auto &fx = proj.proj_effects;
 
     if( ( gun.ammo_data() && gun.ammo_data()->phase == phase_id::LIQUID ) ||