Damage movespeed (#5244)

Content.Shared/Damage/Components/SlowOnDamageComponent.cs

@@ -0,0 +1,22 @@
+using System.Collections.Generic;
+using Content.Shared.FixedPoint;
+using Robust.Shared.GameObjects;
+using Robust.Shared.GameStates;
+using Robust.Shared.Serialization.Manager.Attributes;
+
+namespace Content.Shared.Damage.Components
+{
+    // TODO It'd be nice if this could be a destructible threshold, but on the other hand,
+    // that doesn't really work with events at all, and
+    [RegisterComponent, NetworkedComponent]
+    public class SlowOnDamageComponent : Component
+    {
+        public override string Name => "SlowOnDamage";
+
+        /// <summary>
+        ///     Damage -> movespeed dictionary. This is -damage-, not -health-.
+        /// </summary>
+        [DataField("speedModifierThresholds", required: true)]
+        public readonly Dictionary<FixedPoint2, float> SpeedModifierThresholds = default!;
+    }
+}

Content.Shared/Damage/Systems/DamageableSystem.cs

@@ -2,6 +2,7 @@ using System.Collections.Generic;
 using System.Linq;
 using Content.Shared.Damage.Prototypes;
 using Content.Shared.FixedPoint;
+using Content.Shared.Movement.EntitySystems;
 using Robust.Shared.GameObjects;
 using Robust.Shared.GameStates;
 using Robust.Shared.IoC;

Content.Shared/Damage/Systems/SlowOnDamageSystem.cs

@@ -0,0 +1,54 @@
+using System;
+using Content.Shared.Damage.Components;
+using Content.Shared.FixedPoint;
+using Content.Shared.Movement.EntitySystems;
+using Robust.Shared.GameObjects;
+using Robust.Shared.IoC;
+
+namespace Content.Shared.Damage.Systems
+{
+    public class SlowOnDamageSystem : EntitySystem
+    {
+        [Dependency] private readonly MovementSpeedModifierSystem _movementSpeedModifierSystem = default!;
+
+        public override void Initialize()
+        {
+            base.Initialize();
+
+            SubscribeLocalEvent<SlowOnDamageComponent, DamageChangedEvent>(OnDamageChanged);
+            SubscribeLocalEvent<SlowOnDamageComponent, RefreshMovementSpeedModifiersEvent>(OnRefreshMovespeed);
+        }
+
+        private void OnRefreshMovespeed(EntityUid uid, SlowOnDamageComponent component, RefreshMovementSpeedModifiersEvent args)
+        {
+            if (!EntityManager.TryGetComponent<DamageableComponent>(uid, out var damage))
+                return;
+
+            if (damage.TotalDamage == FixedPoint2.Zero)
+                return;
+
+            // Get closest threshold
+            FixedPoint2 closest = FixedPoint2.Zero;
+            var total = damage.TotalDamage;
+            foreach (var thres in component.SpeedModifierThresholds)
+            {
+                if (FixedPoint2.Dist(thres.Key, total) < FixedPoint2.Dist(closest, total))
+                    closest = thres.Key;
+            }
+
+            if (closest != FixedPoint2.Zero)
+            {
+                var speed = component.SpeedModifierThresholds[closest];
+                args.ModifySpeed(speed, speed);
+            }
+        }
+
+        private void OnDamageChanged(EntityUid uid, SlowOnDamageComponent component, DamageChangedEvent args)
+        {
+            // We -could- only refresh if it crossed a threshold but that would kind of be a lot of duplicated
+            // code and this isn't a super hot path anyway since basically only humans have this
+
+            _movementSpeedModifierSystem.RefreshMovementSpeedModifiers(uid);
+        }
+    }
+}

Content.Shared/FixedPoint/FixedPoint2.cs

@@ -3,6 +3,7 @@ using System.Collections;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
+using Content.Shared.ActionBlocker;
 using Robust.Shared.Serialization;
 
 namespace Content.Shared.FixedPoint
@@ -210,6 +211,16 @@ namespace Content.Shared.FixedPoint
             return a > b ? a : b;
         }
 
+        public static FixedPoint2 Abs(FixedPoint2 a)
+        {
+            return FixedPoint2.New(Math.Abs(a._value));
+        }
+
+        public static FixedPoint2 Dist(FixedPoint2 a, FixedPoint2 b)
+        {
+            return FixedPoint2.Abs(a - b);
+        }
+
         public static FixedPoint2 Clamp(FixedPoint2 reagent, FixedPoint2 min, FixedPoint2 max)
         {
             if (min > max)

Resources/Prototypes/Entities/Mobs/Species/human.yml

@@ -232,6 +232,12 @@
         damage: 400
       behaviors:
       - !type:GibBehavior { }
+  - type: SlowOnDamage
+    speedModifierThresholds:
+      40: 0.8
+      60: 0.6
+      80: 0.4
+      90: 0.2
   - type: HeatResistance
   - type: Appearance
     visuals: