Add travelled distance with sign to scripts

Author: cesarBLG

Source/Orts.Simulation/Common/Scripting/TrainControlSystem.cs

@@ -273,6 +273,10 @@ public abstract class TrainControlSystem : AbstractTrainScriptClass
         /// </summary>
         public Func<float> LineSpeedMpS;
         /// <summary>
+        /// Running total of distance travelled - negative or positive depending on train direction
+        /// </summary>
+        public Func<float> SignedDistanceM;
+        /// <summary>
         /// True if starting from terminal station (no track behind the train).
         /// </summary>
         public Func<bool> DoesStartFromTerminalStation;

Source/Orts.Simulation/Simulation/RollingStocks/SubSystems/TrainControlSystem.cs

@@ -373,6 +373,7 @@ public void Initialize()
                 Script.AltitudeM = () => Locomotive.WorldPosition.Location.Y;
                 Script.CurrentGradientPercent = () => -Locomotive.CurrentElevationPercent;
                 Script.LineSpeedMpS = () => (float)Simulator.TRK.Tr_RouteFile.SpeedLimit;
+                Script.SignedDistanceM = () => Locomotive.Train.DistanceTravelledM;
                 Script.DoesStartFromTerminalStation = () => DoesStartFromTerminalStation();
                 Script.IsColdStart = () => Locomotive.Train.ColdStart;
                 Script.GetTrackNodeOffset = () => Locomotive.Train.FrontTDBTraveller.TrackNodeLength - Locomotive.Train.FrontTDBTraveller.TrackNodeOffset;