Add sprite fades for occluding sprites (#13267)

Content.Client/Sprite/FadingSpriteComponent.cs

@@ -0,0 +1,13 @@
+using Content.Shared.Sprite;
+
+namespace Content.Client.Sprite;
+
+/// <summary>
+/// The non-networked client-only component to track active <see cref="SpriteFadeComponent"/>
+/// </summary>
+[RegisterComponent, Access(typeof(SpriteFadeSystem))]
+public sealed class FadingSpriteComponent : Component
+{
+    [ViewVariables]
+    public float OriginalAlpha;
+}

Content.Client/Sprite/SpriteFadeSystem.cs

@@ -0,0 +1,102 @@
+using Content.Client.Gameplay;
+using Content.Shared.Sprite;
+using Robust.Client.GameObjects;
+using Robust.Client.Player;
+using Robust.Client.State;
+
+namespace Content.Client.Sprite;
+
+public sealed class SpriteFadeSystem : EntitySystem
+{
+    /*
+     * If the player entity is obstructed under the specified components then it will drop the alpha for that entity
+     * so the player is still visible.
+     */
+
+    [Dependency] private readonly IPlayerManager _playerManager = default!;
+    [Dependency] private readonly IStateManager _stateManager = default!;
+
+    private readonly HashSet<FadingSpriteComponent> _comps = new();
+
+    private const float TargetAlpha = 0.4f;
+    private const float ChangeRate = 1f;
+
+    public override void Initialize()
+    {
+        base.Initialize();
+        SubscribeLocalEvent<FadingSpriteComponent, ComponentShutdown>(OnFadingShutdown);
+    }
+
+    private void OnFadingShutdown(EntityUid uid, FadingSpriteComponent component, ComponentShutdown args)
+    {
+        if (MetaData(uid).EntityLifeStage >= EntityLifeStage.Terminating || !TryComp<SpriteComponent>(uid, out var sprite))
+            return;
+
+        sprite.Color = sprite.Color.WithAlpha(component.OriginalAlpha);
+    }
+
+    public override void FrameUpdate(float frameTime)
+    {
+        base.FrameUpdate(frameTime);
+
+        var player = _playerManager.LocalPlayer?.ControlledEntity;
+        var spriteQuery = GetEntityQuery<SpriteComponent>();
+        var change = ChangeRate * frameTime;
+
+        if (TryComp<TransformComponent>(player, out var playerXform) &&
+            _stateManager.CurrentState is GameplayState state &&
+            spriteQuery.TryGetComponent(player, out var playerSprite))
+        {
+            var fadeQuery = GetEntityQuery<SpriteFadeComponent>();
+            var mapPos = playerXform.MapPosition;
+
+            // Also want to handle large entities even if they may not be clickable.
+            foreach (var ent in state.GetClickableEntities(mapPos))
+            {
+                if (ent == player ||
+                    !fadeQuery.HasComponent(ent) ||
+                    !spriteQuery.TryGetComponent(ent, out var sprite) ||
+                    sprite.DrawDepth < playerSprite.DrawDepth)
+                {
+                    continue;
+                }
+
+                if (!TryComp<FadingSpriteComponent>(ent, out var fading))
+                {
+                    fading = AddComp<FadingSpriteComponent>(ent);
+                    fading.OriginalAlpha = sprite.Color.A;
+                }
+
+                _comps.Add(fading);
+                var newColor = Math.Max(sprite.Color.A - change, TargetAlpha);
+
+                if (!sprite.Color.A.Equals(newColor))
+                {
+                    sprite.Color = sprite.Color.WithAlpha(newColor);
+                }
+            }
+        }
+
+        foreach (var comp in EntityQuery<FadingSpriteComponent>(true))
+        {
+            if (_comps.Contains(comp))
+                continue;
+
+            if (!spriteQuery.TryGetComponent(comp.Owner, out var sprite))
+                continue;
+
+            var newColor = Math.Min(sprite.Color.A + change, comp.OriginalAlpha);
+
+            if (!newColor.Equals(sprite.Color.A))
+            {
+                sprite.Color = sprite.Color.WithAlpha(newColor);
+            }
+            else
+            {
+                RemCompDeferred<FadingSpriteComponent>(comp.Owner);
+            }
+        }
+
+        _comps.Clear();
+    }
+}

Content.Shared/Sprite/SpriteFadeComponent.cs

@@ -0,0 +1,12 @@
+using Robust.Shared.GameStates;
+
+namespace Content.Shared.Sprite;
+
+/// <summary>
+/// If your client entity is behind this then the sprite's alpha will be lowered so your entity remains visible.
+/// </summary>
+[RegisterComponent, NetworkedComponent]
+public sealed class SpriteFadeComponent : Component
+{
+
+}

Resources/Prototypes/Entities/Objects/Decoration/flora.yml

@@ -37,6 +37,7 @@
   description: Yep, it's a tree.
   abstract: true
   components:
+  - type: SpriteFade
   - type: Clickable
   - type: Sprite
     sprite: Objects/Decoration/Flora/flora_trees.rsi