Lag compensation for wide attacks (#15877)

Content.Client/Weapons/Melee/MeleeWeaponSystem.cs

@@ -1,3 +1,4 @@
+using System.Linq;
 using Content.Client.Gameplay;
 using Content.Shared.CombatMode;
 using Content.Shared.Hands.Components;
@@ -142,7 +143,7 @@ public sealed partial class MeleeWeaponSystem : SharedMeleeWeaponSystem
                     coordinates = EntityCoordinates.FromMap(MapManager.GetMapEntityId(mousePos.MapId), mousePos, _transform, EntityManager);
                 }
 
-                EntityManager.RaisePredictiveEvent(new HeavyAttackEvent(weaponUid, coordinates));
+                ClientHeavyAttack(entity, coordinates, weaponUid, weapon);
             }
 
             return;
@@ -244,6 +245,31 @@ public sealed partial class MeleeWeaponSystem : SharedMeleeWeaponSystem
         return true;
     }
 
+    /// <summary>
+    /// Raises a heavy attack event with the relevant attacked entities.
+    /// This is to avoid lag effecting the client's perspective too much.
+    /// </summary>
+    private void ClientHeavyAttack(EntityUid user, EntityCoordinates coordinates, EntityUid meleeUid, MeleeWeaponComponent component)
+    {
+        // Only run on first prediction to avoid the potential raycast entities changing.
+        if (!TryComp<TransformComponent>(user, out var userXform) || !Timing.IsFirstTimePredicted)
+            return;
+
+        var targetMap = coordinates.ToMap(EntityManager, _transform);
+
+        if (targetMap.MapId != userXform.MapID)
+            return;
+
+        var userPos = _transform.GetWorldPosition(userXform);
+        var direction = targetMap.Position - userPos;
+        var distance = Math.Min(component.Range, direction.Length);
+
+        // This should really be improved. GetEntitiesInArc uses pos instead of bounding boxes.
+        // Server will validate it with InRangeUnobstructed.
+        var entities = ArcRayCast(userPos, direction.ToWorldAngle(), component.Angle, distance, userXform.MapID, user);
+        RaisePredictiveEvent(new HeavyAttackEvent(meleeUid, entities.ToList(), coordinates));
+    }
+
     protected override void Popup(string message, EntityUid? uid, EntityUid? user)
     {
         if (!Timing.IsFirstTimePredicted || uid == null)