Clown shoes make you waddle, as God intended

Content.Client/Clothing/Systems/Clown/WaddleClothingSystem.cs

@@ -0,0 +1,26 @@
+using Content.Shared.Clothing.Components.Clown;
+using Content.Shared.Clown;
+using Content.Shared.Inventory.Events;
+
+namespace Content.Client.Clothing.Systems.Clown;
+
+public sealed class WaddleClothingSystem : EntitySystem
+{
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        SubscribeLocalEvent<WaddleComponent, GotEquippedEvent>(OnGotEquipped);
+        SubscribeLocalEvent<WaddleComponent, GotUnequippedEvent>(OnGotUnequipped);
+    }
+
+    private void OnGotEquipped(EntityUid entity, WaddleComponent comp, GotEquippedEvent args)
+    {
+        EnsureComp<WaddleAnimationComponent>(args.Equipee);
+    }
+
+    private void OnGotUnequipped(EntityUid entity, WaddleComponent comp, GotUnequippedEvent args)
+    {
+        RemComp<WaddleAnimationComponent>(args.Equipee);
+    }
+}

Content.Client/Clown/WaddleAnimationSystem.cs

@@ -0,0 +1,130 @@
+using System.Numerics;
+using Content.Client.Gravity;
+using Content.Shared.Clown;
+using Content.Shared.Movement.Components;
+using Content.Shared.Movement.Events;
+using Content.Shared.Movement.Systems;
+using Robust.Client.Animations;
+using Robust.Client.GameObjects;
+using Robust.Shared.Animations;
+using Robust.Shared.Timing;
+
+namespace Content.Client.Clown;
+
+public sealed class WaddleAnimationSystem : EntitySystem
+{
+    [Dependency] private readonly AnimationPlayerSystem _animation = default!;
+    [Dependency] private readonly GravitySystem _gravity = default!;
+    [Dependency] private readonly IGameTiming _timing = default!;
+
+    public override void Initialize()
+    {
+        SubscribeLocalEvent<WaddleAnimationComponent, MoveInputEvent>(OnMovementInput);
+        SubscribeLocalEvent<WaddleAnimationComponent, StartedWaddlingEvent>(OnStartedWalking);
+        SubscribeLocalEvent<WaddleAnimationComponent, StoppedWaddlingEvent>(OnStoppedWalking);
+        SubscribeLocalEvent<WaddleAnimationComponent, AnimationCompletedEvent>(OnAnimationCompleted);
+    }
+
+    private void OnMovementInput(EntityUid entity, WaddleAnimationComponent component, MoveInputEvent args)
+    {
+        // Prediction mitigation. Prediction means that MoveInputEvents are spammed repeatedly, even though you'd assume
+        // they're once-only for the user actually doing something. As such do nothing if we're just repeating this FoR.
+        if (!_timing.IsFirstTimePredicted)
+        {
+            return;
+        }
+
+        if (args.Component.HeldMoveButtons == MoveButtons.None && component.IsCurrentlyWaddling)
+        {
+            component.IsCurrentlyWaddling = false;
+
+            RaiseLocalEvent(entity, new StoppedWaddlingEvent(entity));
+
+            return;
+        }
+
+        if (component.IsCurrentlyWaddling)
+            return;
+
+        component.IsCurrentlyWaddling = true;
+
+        RaiseLocalEvent(entity, new StartedWaddlingEvent(entity));
+    }
+
+    private void OnStartedWalking(EntityUid uid, WaddleAnimationComponent component, StartedWaddlingEvent args)
+    {
+        if (_animation.HasRunningAnimation(uid, component.KeyName))
+        {
+            return;
+        }
+
+        if (!TryComp<InputMoverComponent>(uid, out var mover))
+        {
+            return;
+        }
+
+        if (_gravity.IsWeightless(uid))
+        {
+            return;
+        }
+
+        var tumbleIntensity = component.LastStep ? 360 - component.TumbleIntensity : component.TumbleIntensity;
+        var len = mover.Sprinting ? component.AnimationLength / 2 : component.AnimationLength;
+
+        component.LastStep = !component.LastStep;
+        component.IsCurrentlyWaddling = true;
+
+        var anim = new Animation()
+        {
+            Length = TimeSpan.FromSeconds(len),
+            AnimationTracks =
+            {
+                new AnimationTrackComponentProperty()
+                {
+                    ComponentType = typeof(SpriteComponent),
+                    Property = nameof(SpriteComponent.Rotation),
+                    InterpolationMode = AnimationInterpolationMode.Linear,
+                    KeyFrames =
+                    {
+                        new AnimationTrackProperty.KeyFrame(Angle.FromDegrees(0), 0),
+                        new AnimationTrackProperty.KeyFrame(Angle.FromDegrees(tumbleIntensity), len/2),
+                        new AnimationTrackProperty.KeyFrame(Angle.FromDegrees(0), len/2),
+                    }
+                },
+                new AnimationTrackComponentProperty()
+                {
+                    ComponentType = typeof(SpriteComponent),
+                    Property = nameof(SpriteComponent.Offset),
+                    InterpolationMode = AnimationInterpolationMode.Linear,
+                    KeyFrames =
+                    {
+                        new AnimationTrackProperty.KeyFrame(new Vector2(), 0),
+                        new AnimationTrackProperty.KeyFrame(component.HopIntensity, len/2),
+                        new AnimationTrackProperty.KeyFrame(new Vector2(), len/2),
+                    }
+                }
+            }
+        };
+
+        _animation.Play(uid, anim, component.KeyName);
+    }
+
+    private void OnStoppedWalking(EntityUid uid, WaddleAnimationComponent component, StoppedWaddlingEvent args)
+    {
+        _animation.Stop(uid, component.KeyName);
+
+        if (!TryComp<SpriteComponent>(uid, out var sprite))
+        {
+            return;
+        }
+
+        sprite.Offset = new Vector2();
+        sprite.Rotation = Angle.FromDegrees(0);
+        component.IsCurrentlyWaddling = false;
+    }
+
+    private void OnAnimationCompleted(EntityUid uid, WaddleAnimationComponent component, AnimationCompletedEvent args)
+    {
+        RaiseLocalEvent(uid, new StartedWaddlingEvent(uid));
+    }
+}

Content.Shared/Clothing/Components/Clown/Waddle.cs

@@ -0,0 +1,29 @@
+using System.Numerics;
+
+namespace Content.Shared.Clothing.Components.Clown;
+
+/// <summary>
+/// Defines something as causing waddling when worn.
+/// </summary>
+[RegisterComponent]
+public sealed partial class WaddleComponent : Component
+{
+    ///<summary>
+    /// How high should they hop during the waddle? Higher hop = more energy.
+    /// </summary>
+    [DataField]
+    public Vector2 HopIntensity = new(0, 0.25f);
+
+    /// <summary>
+    /// How far should they rock backward and forward during the waddle?
+    /// Each step will alternate between this being a positive and negative rotation. More rock = more scary.
+    /// </summary>
+    [DataField]
+    public float TumbleIntensity = 20.0f;
+
+    /// <summary>
+    /// How long should a complete step take? Less time = more chaos.
+    /// </summary>
+    [DataField]
+    public float AnimationLength = 0.75f;
+}

Content.Shared/Clown/WaddleAnimationComponent.cs

@@ -0,0 +1,64 @@
+using System.Numerics;
+
+namespace Content.Shared.Clown;
+
+/// <summary>
+/// Declares that an entity has started to waddle like a duck/clown.
+/// </summary>
+/// <param name="entity">The newly be-waddled.</param>
+public struct StartedWaddlingEvent(EntityUid entity)
+{
+    public EntityUid Entity = entity;
+}
+
+/// <summary>
+/// Declares that an entity has stopped waddling like a duck/clown.
+/// </summary>
+/// <param name="entity">The former waddle-er.</param>
+public struct StoppedWaddlingEvent(EntityUid entity)
+{
+    public EntityUid Entity = entity;
+}
+
+/// <summary>
+/// Defines something as having a waddle animation when it moves.
+/// </summary>
+[RegisterComponent]
+public sealed partial class WaddleAnimationComponent : Component
+{
+    /// <summary>
+    /// What's the name of this animation? Make sure it's unique so it can play along side other animations.
+    /// This prevents someone accidentally causing two identical waddling effects to play on someone at the same time.
+    /// </summary>
+    [DataField]
+    public string KeyName = "Waddle";
+
+    ///<summary>
+    /// How high should they hop during the waddle? Higher hop = more energy.
+    /// </summary>
+    [DataField]
+    public Vector2 HopIntensity = new(0, 0.25f);
+
+    /// <summary>
+    /// How far should they rock backward and forward during the waddle?
+    /// Each step will alternate between this being a positive and negative rotation. More rock = more scary.
+    /// </summary>
+    [DataField]
+    public float TumbleIntensity = 20.0f;
+
+    /// <summary>
+    /// How long should a complete step take? Less time = more chaos.
+    /// </summary>
+    [DataField]
+    public float AnimationLength = 0.75f;
+
+    /// <summary>
+    /// Stores which step we made last, so if someone cancels out of the animation mid-step then restarts it looks more natural.
+    /// </summary>
+    public bool LastStep;
+
+    /// <summary>
+    /// Stores if we're currently waddling so we can start/stop as appropriate and can tell other systems our state.
+    /// </summary>
+    public bool IsCurrentlyWaddling;
+}

Resources/Prototypes/Entities/Clothing/Shoes/specific.yml

@@ -15,6 +15,7 @@
   parent: [ClothingShoesBaseButcherable, ClothingSlotBase]
   id: ClothingShoesClownBase
   components:
+  - type: Waddle
   - type: ItemSlots
     slots:
       item: