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);
+        }
+    }
+}