Add atmos tick time to atmos device update event (#18781)

Content.Server/Atmos/Piping/Components/AtmosDeviceComponent.cs

@@ -7,32 +7,50 @@ namespace Content.Server.Atmos.Piping.Components
     public sealed class AtmosDeviceComponent : Component
     {
         /// <summary>
-        ///     Whether this device requires being anchored to join an atmosphere.
+        ///     If true, this device must be anchored before it will receive any AtmosDeviceUpdateEvents.
         /// </summary>
         [ViewVariables(VVAccess.ReadWrite)]
         [DataField("requireAnchored")]
         public bool RequireAnchored { get; private set; } = true;
 
         /// <summary>
-        ///     Whether this device will join an entity system to process when not in a grid.
+        ///     If true, update even when there is no grid atmosphere. Normally, atmos devices only
+        ///     update when inside a grid atmosphere, because they work with gases in the environment
+        ///     and won't do anything useful if there is no environment. This is useful for devices
+        ///     like gas canisters whose contents can still react if the canister itself is not inside
+        ///     a grid atmosphere.
         /// </summary>
         [DataField("joinSystem")]
         public bool JoinSystem { get; } = false;
 
         /// <summary>
-        ///     Whether we have joined an entity system to process.
+        ///     If non-null, the grid that this device is part of.
+        /// </summary>
+        public EntityUid? JoinedGrid { get; set; }
+
+        /// <summary>
+        ///     Indicates that a device is not on a grid atmosphere but still being updated.
         /// </summary>
         [ViewVariables]
         public bool JoinedSystem { get; set; } = false;
 
         [ViewVariables]
         public TimeSpan LastProcess { get; set; } = TimeSpan.Zero;
-
-        public EntityUid? JoinedGrid { get; set; }
     }
 
     public sealed class AtmosDeviceUpdateEvent : EntityEventArgs
-    {}
+    {
+        /// <summary>
+        /// Time elapsed since last update, in seconds. Multiply values used in the update handler
+        /// by this number to make them tickrate-invariant. Use this number instead of AtmosphereSystem.AtmosTime.
+        /// </summary>
+        public float dt;
+
+        public AtmosDeviceUpdateEvent(float dt)
+        {
+            this.dt = dt;
+        }
+    }
 
     public sealed class AtmosDeviceEnabledEvent : EntityEventArgs
     {}