Add FlyCircleOnIdle

Code by rob-v.

OpenRA.Mods.Gen/OpenRA.Mods.Gen.csproj

@@ -114,6 +114,7 @@
     <Compile Include="Traits\EmitInfantryOnDeath.cs" />
     <Compile Include="Traits\Air\BlimpFallsToEarth.cs" />
     <Compile Include="Traits\Air\AutoTakesOff.cs" />
+    <Compile Include="Traits\Air\FlyCircleOnIdle.cs" />
     <Compile Include="Traits\CargoCashTrickler.cs" />
     <Compile Include="Traits\CargoTransformer.cs" />
     <Compile Include="Traits\Conditions\GrantTimedConditionOnDeploy.cs" />

OpenRA.Mods.Gen/Traits/Air/FlyCircleOnIdle.cs

@@ -0,0 +1,42 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2018 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 OpenRA.Mods.Common.Activities;
+using OpenRA.Mods.Common.Traits;
+using OpenRA.Traits;
+
+namespace OpenRA.Mods.Yupgi_alert.Traits
+{
+	[Desc("Fly in circle while idle (on stop,..).")]
+	public class FlyCircleOnIdleInfo : ITraitInfo, Requires<AircraftInfo>
+	{
+		public object Create(ActorInitializer init) { return new FlyCircleOnIdle(init.Self, this); }
+	}
+
+	public class FlyCircleOnIdle : INotifyIdle
+	{
+		readonly AircraftInfo aircraftInfo;
+
+		public FlyCircleOnIdle(Actor self, FlyCircleOnIdleInfo info)
+		{
+			aircraftInfo = self.Info.TraitInfo<AircraftInfo>();
+		}
+
+		public void TickIdle(Actor self)
+		{
+			// We're on the ground, let's stay there.
+			if (self.World.Map.DistanceAboveTerrain(self.CenterPosition).Length < aircraftInfo.MinAirborneAltitude)
+				return;
+
+			self.QueueActivity(new FlyCircle(self));
+		}
+	}
+}