Introduce IDefaultVisibility.

OpenRA.Mods.Common/Traits/Modifiers/HiddenUnderShroud.cs

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+#region Copyright & License Information
+/*
+ * Copyright 2007-2015 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using OpenRA.Graphics;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common.Traits
+{
+	[Desc("The actor stays invisible under the shroud.")]
+	public class HiddenUnderShroudInfo : ITraitInfo, IDefaultVisibilityInfo
+	{
+		[Desc("Players with these stances can always see the actor.")]
+		public readonly Stance AlwaysVisibleStances = Stance.Ally;
+
+		public virtual object Create(ActorInitializer init) { return new HiddenUnderShroud(this); }
+	}
+
+	public class HiddenUnderShroud : IDefaultVisibility, IRenderModifier
+	{
+		readonly HiddenUnderShroudInfo info;
+
+		public HiddenUnderShroud(HiddenUnderShroudInfo info)
+		{
+			this.info = info;
+		}
+
+		protected IEnumerable<CPos> VisibilityFootprint(Actor self)
+		{
+			return Shroud.GetVisOrigins(self);
+		}
+
+		protected virtual bool IsVisibleInner(Actor self, Player byPlayer)
+		{
+			return VisibilityFootprint(self).Any(byPlayer.Shroud.IsExplored);
+		}
+
+		public bool IsVisible(Actor self, Player byPlayer)
+		{
+			if (byPlayer == null)
+				return true;
+
+			var stance = self.Owner.Stances[byPlayer];
+			return info.AlwaysVisibleStances.HasFlag(stance) || IsVisibleInner(self, byPlayer);
+		}
+
+		public IEnumerable<IRenderable> ModifyRender(Actor self, WorldRenderer wr, IEnumerable<IRenderable> r)
+		{
+			return IsVisible(self, self.World.RenderPlayer) ? r : SpriteRenderable.None;
+		}
+	}
+}