Fireplaces are warm, books are burnable, burn papers with fireplaces

Content.Client/Paper/UI/PaperVisualizerSystem.cs

@@ -1,3 +1,4 @@
+using Content.Shared.Tag;
 using Robust.Client.GameObjects;
 
 using static Content.Shared.Paper.PaperComponent;
@@ -6,9 +7,11 @@ namespace Content.Client.Paper.UI;
 
 public sealed class PaperVisualizerSystem : VisualizerSystem<PaperVisualsComponent>
 {
+    [Dependency] private readonly TagSystem _tagSystem = default!;
+
     protected override void OnAppearanceChange(EntityUid uid, PaperVisualsComponent component, ref AppearanceChangeEvent args)
     {
-        if (args.Sprite == null)
+        if (args.Sprite == null || _tagSystem.HasTag(uid, "Book"))
             return;
 
         if (AppearanceSystem.TryGetData<PaperStatus>(uid, PaperVisuals.Status , out var writingStatus, args.Component))

Content.Server/Atmos/EntitySystems/FlammableSystem.cs

@@ -67,6 +67,7 @@ public override void Initialize()
             _physicsQuery = GetEntityQuery<PhysicsComponent>();
 
             SubscribeLocalEvent<FlammableComponent, MapInitEvent>(OnMapInit);
+            SubscribeLocalEvent<FlammableComponent, AfterInteractEvent>(OnInteract);
             SubscribeLocalEvent<FlammableComponent, InteractUsingEvent>(OnInteractUsing);
             SubscribeLocalEvent<FlammableComponent, StartCollideEvent>(OnCollide);
             SubscribeLocalEvent<FlammableComponent, IsHotEvent>(OnIsHot);
@@ -139,6 +140,25 @@ private void OnMapInit(EntityUid uid, FlammableComponent component, MapInitEvent
                 collisionMask: (int) CollisionGroup.FullTileLayer, body: body);
         }
 
+        /// <summary>
+        /// Using something flammable on something that's hot (fireplace, e-sword, lighter) will ignite the item
+        /// Example: burning paper by using it on a fireplace
+        /// </summary>
+        private void OnInteract(Entity<FlammableComponent> entity, ref AfterInteractEvent args)
+        {
+            if (args.Handled || args.Target == null)
+                return;
+
+            var isHotEvent = new IsHotEvent();
+            RaiseLocalEvent(args.Target.Value, isHotEvent);
+
+            if (!isHotEvent.IsHot)
+                return;
+
+            Ignite(entity, args.Used, entity.Comp, args.User);
+            args.Handled = true;
+        }
+
         private void OnInteractUsing(EntityUid uid, FlammableComponent flammable, InteractUsingEvent args)
         {
             if (args.Handled)

Content.Server/Temperature/Components/RadiantTemperatureComponent.cs

@@ -0,0 +1,24 @@
+using Content.Shared.Atmos;
+
+namespace Content.Server.Temperature.Components;
+
+/// <summary>
+/// The entity will cause the surrounding air temperature to change passively without
+/// any need for power or anything else.
+/// </summary>
+[RegisterComponent]
+public sealed partial class RadiantTemperatureComponent : Component
+{
+    /// <summary>
+    /// The temperature that the entity will try to reach
+    /// </summary>
+    [DataField]
+    public float GoalTemperature = Atmospherics.T20C;
+
+    /// <summary>
+    /// How much the temperature of the surrounding air will change in Kelvin per tick
+    /// Positive means it will only heat, negative means it will only cool
+    /// </summary>
+    [DataField]
+    public float TemperatureChangePerTick = 1f;
+}

Content.Server/Temperature/Systems/RadiantTemperatureSystem.cs

@@ -0,0 +1,40 @@
+using Content.Server.Atmos.EntitySystems;
+using Content.Server.Temperature.Components;
+using Robust.Server.GameObjects;
+
+namespace Content.Server.Temperature.Systems;
+
+public sealed class RadiantTemperatureSystem : EntitySystem
+{
+    [Dependency] private readonly AtmosphereSystem _atmosphere = default!;
+    [Dependency] private readonly TransformSystem _xform = default!;
+
+    public override void Update(float frameTime)
+    {
+        base.Update(frameTime);
+
+        var query = EntityQueryEnumerator<RadiantTemperatureComponent, TransformComponent>();
+        while (query.MoveNext(out var ent, out var comp, out var xform))
+        {
+            var grid = xform.GridUid;
+            var map = xform.MapUid;
+            var indices = _xform.GetGridTilePositionOrDefault((ent, xform));
+            var mixture = _atmosphere.GetTileMixture(grid, map, indices, true);
+
+            if (mixture is null)
+                continue;
+
+            // do not continue heating if air is hotter than goal temperature,
+            // and the entity is a radiant HEAT source (positive temp changes)
+            if (mixture.Temperature > comp.GoalTemperature && comp.TemperatureChangePerTick > 0)
+                continue;
+
+            // do not continue cooling if air is colder than goal temperature
+            // and the entity is a radiant COOLING source (negative temp changes)
+            if (mixture.Temperature < comp.GoalTemperature && comp.TemperatureChangePerTick < 0)
+                continue;
+
+            mixture.Temperature += comp.TemperatureChangePerTick * frameTime;
+        }
+    }
+}

Resources/Prototypes/Entities/Objects/Misc/books.yml

@@ -43,6 +43,33 @@
     damage:
       types:
         Blunt: 1
+  - type: Flammable
+    fireSpread: true
+    canResistFire: false
+    alwaysCombustible: true
+    canExtinguish: true # save the books!
+    damage:
+      types:
+        Heat: 1
+  - type: Appearance
+  - type: FireVisuals
+    sprite: Effects/fire.rsi
+    normalState: fire
+  - type: Damageable
+    damageModifierSet: Wood
+  - type: Destructible
+    thresholds:
+    - trigger:
+        !type:DamageTrigger
+        damage: 40 # sure does take a lot longer to burn a book than a piece of paper
+      behaviors:
+      - !type:SpawnEntitiesBehavior
+        spawn:
+          Ash:
+            min: 1
+            max: 1
+      - !type:DoActsBehavior
+        acts: [ "Destruction" ]
 
 - type: entity
   parent: BaseItem

Resources/Prototypes/Entities/Structures/Decoration/bonfire.yml

@@ -31,6 +31,11 @@
     sound:
       path: /Audio/Ambience/Objects/fireplace.ogg
   - type: AlwaysHot
+  - type: IgnitionSource
+    ignited: true
+  - type: RadiantTemperature
+    goalTemperature: 305
+    temperatureChangePerTick: 30
 
 - type: entity
   id: LegionnaireBonfire

Resources/Prototypes/Entities/Structures/Decoration/fireplace.yml

@@ -46,3 +46,8 @@
           - !type:DoActsBehavior
             acts: [ "Destruction" ]
   - type: AlwaysHot
+  - type: IgnitionSource
+    ignited: true
+  - type: RadiantTemperature
+    goalTemperature: 305
+    temperatureChangePerTick: 30