Extract contrail fading for dead projectiles into an IEffect.

OpenRA.Mods.RA/Effects/ContrailFader.cs

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+#region Copyright & License Information
+/*
+ * Copyright 2007-2013 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 OpenRA.Effects;
+using OpenRA.Graphics;
+
+namespace OpenRA.Mods.RA.Effects
+{
+	class ContrailFader : IEffect
+	{
+		WPos pos;
+		ContrailRenderable trail;
+
+		public ContrailFader(WPos pos, ContrailRenderable trail)
+		{
+			this.pos = pos;
+			this.trail = trail;
+		}
+
+		public void Tick(World world)
+		{
+			trail.Update(pos);
+		}
+
+		public IEnumerable<IRenderable> Render(WorldRenderer wr)
+		{
+			yield return trail;
+		}
+	}
+}