Make Contrail conditional and public

Also moved it to 'Render' subfolder while at it.

OpenRA.Mods.Common/Traits/Render/Contrail.cs

@@ -0,0 +1,92 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2021 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, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using OpenRA.Graphics;
+using OpenRA.Mods.Common.Graphics;
+using OpenRA.Primitives;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Common.Traits
+{
+	[Desc("Draw a colored contrail behind this actor when they move.")]
+	public class ContrailInfo : ConditionalTraitInfo, Requires<BodyOrientationInfo>
+	{
+		[Desc("Position relative to body")]
+		public readonly WVec Offset = WVec.Zero;
+
+		[Desc("Offset for Z sorting.")]
+		public readonly int ZOffset = 0;
+
+		[Desc("Length of the trail (in ticks).")]
+		public readonly int TrailLength = 25;
+
+		[Desc("Width of the trail.")]
+		public readonly WDist TrailWidth = new WDist(64);
+
+		[Desc("RGB color of the contrail.")]
+		public readonly Color Color = Color.White;
+
+		[Desc("Use player remap color instead of a custom color?")]
+		public readonly bool UsePlayerColor = true;
+
+		public override object Create(ActorInitializer init) { return new Contrail(init.Self, this); }
+	}
+
+	public class Contrail : ConditionalTrait<ContrailInfo>, ITick, IRender, INotifyAddedToWorld
+	{
+		readonly ContrailInfo info;
+		readonly BodyOrientation body;
+		readonly Color color;
+
+		// This is a mutable struct, so it can't be readonly.
+		ContrailRenderable trail;
+
+		public Contrail(Actor self, ContrailInfo info)
+			: base(info)
+		{
+			this.info = info;
+
+			color = info.UsePlayerColor ? ContrailRenderable.ChooseColor(self) : info.Color;
+			trail = new ContrailRenderable(self.World, color, info.TrailWidth, info.TrailLength, 0, info.ZOffset);
+
+			body = self.Trait<BodyOrientation>();
+		}
+
+		void ITick.Tick(Actor self)
+		{
+			// We want to update the trails' position even while the trait is disabled,
+			// otherwise we might get visual 'jumps' when the trait is re-enabled.
+			var local = info.Offset.Rotate(body.QuantizeOrientation(self, self.Orientation));
+			trail.Update(self.CenterPosition + body.LocalToWorld(local));
+		}
+
+		IEnumerable<IRenderable> IRender.Render(Actor self, WorldRenderer wr)
+		{
+			if (IsTraitDisabled)
+				return Enumerable.Empty<IRenderable>();
+
+			return new IRenderable[] { trail };
+		}
+
+		IEnumerable<Rectangle> IRender.ScreenBounds(Actor self, WorldRenderer wr)
+		{
+			// Contrails don't contribute to actor bounds
+			yield break;
+		}
+
+		void INotifyAddedToWorld.AddedToWorld(Actor self)
+		{
+			trail = new ContrailRenderable(self.World, color, info.TrailWidth, info.TrailLength, 0, info.ZOffset);
+		}
+	}
+}