Clown shoes make you waddle, as God intended (#26338)

* Clown shoes make you waddle, as God intended

* OOPS

* Toned down, client system name fix

* Tidy namespacing for @deltanedas

* Refactor to handle prediction better, etc.

* Resolve PR comments.

Content.Client/Movement/Systems/WaddleAnimationSystem.cs

@@ -0,0 +1,135 @@
+using System.Numerics;
+using Content.Client.Gravity;
+using Content.Shared.Movement.Components;
+using Content.Shared.Movement.Events;
+using Robust.Client.Animations;
+using Robust.Client.GameObjects;
+using Robust.Shared.Animations;
+using Robust.Shared.Timing;
+
+namespace Content.Client.Movement.Systems;
+
+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.HasDirectionalMovement && component.IsCurrentlyWaddling)
+        {
+            component.IsCurrentlyWaddling = false;
+
+            var stopped = new StoppedWaddlingEvent(entity);
+
+            RaiseLocalEvent(entity, ref stopped);
+
+            return;
+        }
+
+        // Only start waddling if we're not currently AND we're actually moving.
+        if (component.IsCurrentlyWaddling || !args.HasDirectionalMovement)
+            return;
+
+        component.IsCurrentlyWaddling = true;
+
+        var started = new StartedWaddlingEvent(entity);
+
+        RaiseLocalEvent(entity, ref started);
+    }
+
+    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 * component.RunAnimationLengthMultiplier : 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)
+    {
+        var started = new StartedWaddlingEvent(uid);
+
+        RaiseLocalEvent(uid, ref started);
+    }
+}