Fix collisions passing firestacks between mobs (#9324)

Content.Server/Atmos/Components/FlammableComponent.cs

@@ -1,4 +1,5 @@
 using Content.Shared.Damage;
+using Robust.Shared.Physics.Collision.Shapes;
 
 namespace Content.Server.Atmos.Components
 {
@@ -28,5 +29,11 @@ namespace Content.Server.Atmos.Components
         [DataField("damage", required: true)]
         [ViewVariables(VVAccess.ReadWrite)]
         public DamageSpecifier Damage = new(); // Empty by default, we don't want any funny NREs.
+
+        /// <summary>
+        ///     Used for the fixture created to handle passing firestacks when two flammable objects collide.
+        /// </summary>
+        [DataField("flammableCollisionShape")]
+        public IPhysShape FlammableCollisionShape = new PhysShapeCircle() { Radius = 0.35f };
     }
 }

Content.Server/Atmos/EntitySystems/FlammableSystem.cs

@@ -12,6 +12,7 @@ using Content.Shared.Atmos;
 using Content.Shared.Damage;
 using Content.Shared.Database;
 using Content.Shared.Interaction;
+using Content.Shared.Physics;
 using Content.Shared.Popups;
 using Content.Shared.Temperature;
 using Robust.Server.GameObjects;
@@ -32,6 +33,7 @@ namespace Content.Server.Atmos.EntitySystems
         [Dependency] private readonly DamageableSystem _damageableSystem = default!;
         [Dependency] private readonly AlertsSystem _alertsSystem = default!;
         [Dependency] private readonly TransformSystem _transformSystem = default!;
+        [Dependency] private readonly FixtureSystem _fixture = default!;
         [Dependency] private readonly IAdminLogManager _adminLogger = default!;
 
         private const float MinimumFireStacks = -10f;
@@ -39,16 +41,17 @@ namespace Content.Server.Atmos.EntitySystems
         private const float UpdateTime = 1f;
 
         private const float MinIgnitionTemperature = 373.15f;
+        public const string FlammableFixtureID = "flammable";
 
         private float _timer = 0f;
 
         private Dictionary<FlammableComponent, float> _fireEvents = new();
 
-        // TODO: Port the rest of Flammable.
         public override void Initialize()
         {
             UpdatesAfter.Add(typeof(AtmosphereSystem));
 
+            SubscribeLocalEvent<FlammableComponent, MapInitEvent>(OnMapInit);
             SubscribeLocalEvent<FlammableComponent, InteractUsingEvent>(OnInteractUsingEvent);
             SubscribeLocalEvent<FlammableComponent, StartCollideEvent>(OnCollideEvent);
             SubscribeLocalEvent<FlammableComponent, IsHotEvent>(OnIsHotEvent);
@@ -81,13 +84,30 @@ namespace Content.Server.Atmos.EntitySystems
             Ignite(otherFixture, flammable);
         }
 
+        private void OnMapInit(EntityUid uid, FlammableComponent component, MapInitEvent args)
+        {
+            // Sets up a fixture for flammable collisions.
+            // TODO: Should this be generalized into a general non-hard 'effects' fixture or something? I can't think of other use cases for it.
+            // This doesn't seem great either (lots more collisions generated) but there isn't a better way to solve it either that I can think of.
+
+            if (!TryComp<PhysicsComponent>(uid, out var body))
+                return;
+
+            _fixture.TryCreateFixture(body, new Fixture(body, component.FlammableCollisionShape)
+            {
+                Hard = false,
+                ID = FlammableFixtureID,
+                CollisionMask = (int) CollisionGroup.FullTileLayer
+            });
+        }
+
         private void OnInteractUsingEvent(EntityUid uid, FlammableComponent flammable, InteractUsingEvent args)
         {
             if (args.Handled)
                 return;
 
             var isHotEvent = new IsHotEvent();
-            RaiseLocalEvent(args.Used, isHotEvent, false);
+            RaiseLocalEvent(args.Used, isHotEvent);
 
             if (!isHotEvent.IsHot)
                 return;
@@ -99,6 +119,12 @@ namespace Content.Server.Atmos.EntitySystems
         private void OnCollideEvent(EntityUid uid, FlammableComponent flammable, StartCollideEvent args)
         {
             var otherUid = args.OtherFixture.Body.Owner;
+
+            // Normal hard collisions, though this isn't generally possible since most flammable things are mobs
+            // which don't collide with one another, shouldn't work here.
+            if (args.OtherFixture.ID != FlammableFixtureID && args.OurFixture.ID != FlammableFixtureID)
+                return;
+
             if (!EntityManager.TryGetComponent(otherUid, out FlammableComponent? otherFlammable))
                 return;
 
@@ -119,7 +145,8 @@ namespace Content.Server.Atmos.EntitySystems
                     otherFlammable.FireStacks += flammable.FireStacks;
                     Ignite(otherUid, otherFlammable);
                 }
-            } else if (otherFlammable.OnFire)
+            }
+            else if (otherFlammable.OnFire)
             {
                 otherFlammable.FireStacks /= 2;
                 flammable.FireStacks += otherFlammable.FireStacks;