Add prediction for standing states and mob states (#1937)

Content.Server/GameObjects/EntitySystems/StandingStateSystem.cs

@@ -0,0 +1,65 @@
+using Content.Server.Interfaces.GameObjects.Components.Items;
+using Content.Shared.Audio;
+using Content.Shared.GameObjects.Components.Rotation;
+using Content.Shared.GameObjects.EntitySystems;
+using JetBrains.Annotations;
+using Robust.Server.GameObjects;
+using Robust.Server.GameObjects.EntitySystems;
+using Robust.Shared.Interfaces.GameObjects;
+
+namespace Content.Server.GameObjects.EntitySystems
+{
+    [UsedImplicitly]
+    public class StandingStateSystem : SharedStandingStateSystem
+    {
+        protected override bool OnDown(IEntity entity, bool playSound = true, bool dropItems = true, bool force = false)
+        {
+            if (!entity.TryGetComponent(out AppearanceComponent appearance))
+            {
+                return false;
+            }
+
+            var newState = RotationState.Horizontal;
+            appearance.TryGetData<RotationState>(RotationVisuals.RotationState, out var oldState);
+
+            if (newState != oldState)
+            {
+                appearance.SetData(RotationVisuals.RotationState, newState);
+            }
+
+            if (playSound)
+            {
+                var file = AudioHelpers.GetRandomFileFromSoundCollection("bodyfall");
+                Get<AudioSystem>().PlayFromEntity(file, entity, AudioHelpers.WithVariation(0.25f));
+            }
+
+            return true;
+        }
+
+        protected override bool OnStand(IEntity entity)
+        {
+            if (!entity.TryGetComponent(out AppearanceComponent appearance)) return false;
+
+            appearance.TryGetData<RotationState>(RotationVisuals.RotationState, out var oldState);
+            var newState = RotationState.Vertical;
+
+            if (newState == oldState) return false;
+
+            appearance.SetData(RotationVisuals.RotationState, newState);
+
+            return true;
+        }
+
+        public override void DropAllItemsInHands(IEntity entity, bool doMobChecks = true)
+        {
+            base.DropAllItemsInHands(entity, doMobChecks);
+
+            if (!entity.TryGetComponent(out IHandsComponent hands)) return;
+
+            foreach (var heldItem in hands.GetAllHeldItems())
+            {
+                hands.Drop(heldItem.Owner, doMobChecks);
+            }
+        }
+    }
+}