Damage visualizer for simple mobs (#1332)

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>
Co-authored-by: Pieter-Jan Briers <pieterjan.briers+git@gmail.com>

Content.Client/GameObjects/Components/Mobs/DamageStateVisualizer.cs

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+using System.Collections.Generic;
+using Content.Shared.GameObjects.Components.Mobs;
+using JetBrains.Annotations;
+using Robust.Client.GameObjects;
+using Robust.Client.Interfaces.GameObjects.Components;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Utility;
+using YamlDotNet.RepresentationModel;
+using DrawDepth = Content.Shared.GameObjects.DrawDepth;
+
+namespace Content.Client.GameObjects.Components.Mobs
+{
+    [UsedImplicitly]
+    public sealed class DamageStateVisualizer : AppearanceVisualizer
+    {
+        private DamageStateVisualData _data = DamageStateVisualData.Normal;
+        private Dictionary<DamageStateVisualData, string> _stateMap = new Dictionary<DamageStateVisualData,string>();
+        private int? _originalDrawDepth = null;
+
+        public override void LoadData(YamlMappingNode node)
+        {
+            base.LoadData(node);
+            if (node.TryGetNode("normal", out var normal))
+            {
+                _stateMap.Add(DamageStateVisualData.Normal, normal.AsString());
+            }
+
+            if (node.TryGetNode("crit", out var crit))
+            {
+                _stateMap.Add(DamageStateVisualData.Crit, crit.AsString());
+            }
+
+            if (node.TryGetNode("dead", out var dead))
+            {
+                _stateMap.Add(DamageStateVisualData.Dead, dead.AsString());
+            }
+        }
+
+        public override void OnChangeData(AppearanceComponent component)
+        {
+            base.OnChangeData(component);
+            var sprite = component.Owner.GetComponent<ISpriteComponent>();
+            if (!component.TryGetData(DamageStateVisuals.State, out DamageStateVisualData data))
+            {
+                return;
+            }
+
+            if (_data == data)
+            {
+                return;
+            }
+
+            _data = data;
+
+            if (_stateMap.TryGetValue(_data, out var state))
+            {
+                sprite.LayerSetState(DamageStateVisualLayers.Base, state);
+            }
+
+            // So they don't draw over mobs anymore
+            if (_data == DamageStateVisualData.Dead)
+            {
+                _originalDrawDepth = sprite.DrawDepth;
+                sprite.DrawDepth = (int) DrawDepth.FloorObjects;
+            }
+            else if (_originalDrawDepth != null)
+            {
+                sprite.DrawDepth = _originalDrawDepth.Value;
+                _originalDrawDepth = null;
+            }
+        }
+    }
+
+    public enum DamageStateVisualLayers
+    {
+        Base
+    }
+}