WiP movement prediction.

Content.Shared/GameObjects/Components/Movement/MovementSpeedModifierComponent.cs

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+using Robust.Shared.GameObjects;
+using Robust.Shared.Serialization;
+using Robust.Shared.ViewVariables;
+
+namespace Content.Shared.GameObjects.Components.Movement
+{
+    [RegisterComponent]
+    public class MovementSpeedModifierComponent : Component
+    {
+        public const float DefaultBaseWalkSpeed = 4.0f;
+        public const float DefaultBaseSprintSpeed = 7.0f;
+
+        public override string Name => "MovementSpeedModifier";
+
+        private float _cachedWalkSpeedModifier = 1.0f;
+        [ViewVariables]
+        public float WalkSpeedModifier
+        {
+            get
+            {
+                RecalculateMovementSpeedModifiers();
+                return _cachedWalkSpeedModifier;
+            }
+        }
+        private float _cachedSprintSpeedModifier;
+        [ViewVariables]
+        public float SprintSpeedModifier
+        {
+            get
+            {
+                RecalculateMovementSpeedModifiers();
+                return _cachedSprintSpeedModifier;
+            }
+        }
+
+        [ViewVariables(VVAccess.ReadWrite)]
+        public float BaseWalkSpeed { get; set; }
+        [ViewVariables(VVAccess.ReadWrite)]
+        public float BaseSprintSpeed { get; set; }
+
+        [ViewVariables]
+        public float CurrentWalkSpeed => WalkSpeedModifier * BaseWalkSpeed;
+        [ViewVariables]
+        public float CurrentSprintSpeed => SprintSpeedModifier * BaseSprintSpeed;
+
+        /// <summary>
+        ///     set to warn us that a component's movespeed modifier has changed
+        /// </summary>
+        private bool _movespeedModifiersNeedRefresh = true;
+
+        public void RefreshMovementSpeedModifiers()
+        {
+            _movespeedModifiersNeedRefresh = true;
+        }
+
+        public override void ExposeData(ObjectSerializer serializer)
+        {
+            base.ExposeData(serializer);
+
+            serializer.DataField(this, p => p.BaseWalkSpeed, "baseWalkSpeed", 4);
+            serializer.DataField(this, p => p.BaseSprintSpeed, "baseSprintSpeed", 7);
+        }
+
+        /// <summary>
+        ///     Recalculate movement speed with current modifiers, or return early if no change
+        /// </summary>
+        private void RecalculateMovementSpeedModifiers()
+        {
+            {
+                if (!_movespeedModifiersNeedRefresh)
+                    return;
+                var movespeedModifiers = Owner.GetAllComponents<IMoveSpeedModifier>();
+                float walkSpeedModifier = 1.0f;
+                float sprintSpeedModifier = 1.0f;
+                foreach (var component in movespeedModifiers)
+                {
+                    walkSpeedModifier *= component.WalkSpeedModifier;
+                    sprintSpeedModifier *= component.SprintSpeedModifier;
+                }
+                _cachedWalkSpeedModifier = walkSpeedModifier;
+                _cachedSprintSpeedModifier = sprintSpeedModifier;
+            }
+            _movespeedModifiersNeedRefresh = false;
+        }
+    }
+
+    public interface IMoveSpeedModifier
+    {
+        float WalkSpeedModifier { get; }
+        float SprintSpeedModifier { get; }
+    }
+}