split various flying behaviors into own files

OpenRa.Game/Traits/Activities/ReturnToBase.cs

@@ -0,0 +1,67 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace OpenRa.Game.Traits.Activities
+{
+	class ReturnToBase : IActivity
+	{
+		public IActivity NextActivity { get; set; }
+		bool isCanceled;
+
+		readonly float2 w1, w2, w3;	/* tangent points to turn circles */
+		readonly float2 landPoint;
+
+		public ReturnToBase(Actor self, float2 landPos)
+		{
+			var unit = self.traits.Get<Unit>();
+			var speed = .2f * Util.GetEffectiveSpeed(self);
+			var approachStart = landPos - new float2(unit.Altitude * speed, 0);
+			var turnRadius = (128f / self.Info.ROT) * speed / (float)Math.PI;
+
+			/* work out the center points */
+			var fwd = -float2.FromAngle(unit.Facing / 128f * (float)Math.PI);
+			var side = new float2(-fwd.Y, fwd.X);		/* rotate */
+			var sideTowardBase = new[] { side, -side }
+				.OrderBy(a => float2.Dot(a, self.CenterLocation - approachStart))
+				.First();
+
+			var c1 = self.CenterLocation + turnRadius * sideTowardBase;
+			var c2 = approachStart + new float2(0,
+				turnRadius * Math.Sign(self.CenterLocation.Y - approachStart.Y));		// above or below start point
+
+			/* work out tangent points */
+			var d = c2 - c1;
+			var e = (turnRadius / d.Length) * d;
+			var f = new float2(-e.Y, e.X);		/* rotate */
+
+			/* todo: support internal tangents, too! */
+
+			if (f.X > 0) f = -f;
+
+			w1 = c1 + f;
+			w2 = c2 + f;
+			w3 = approachStart;
+			landPoint = landPos;
+		}
+
+		public IActivity Tick(Actor self)
+		{
+			if (isCanceled) return NextActivity;
+			var unit = self.traits.Get<Unit>();
+			return new Fly(w1)
+			{
+				NextActivity = new Fly(w2)
+				{
+					NextActivity = new Fly(w3)
+					{
+						NextActivity = new Land(landPoint)
+					}
+				}
+			};
+		}
+
+		public void Cancel(Actor self) { isCanceled = true; NextActivity = null; }
+	}
+}