Add volume controlled curve for back pressure

Author: peternewell

Source/Orts.Formats.Msts/SoundManagmentFile.cs

@@ -240,7 +240,7 @@ public struct CurvePoint
 
     public class VolumeCurve
     {
-        public enum Controls { None, DistanceControlled, SpeedControlled, Variable1Controlled, Variable1_2Controlled, Variable1_3Controlled, Variable1_4Controlled, Variable2Controlled, Variable2BoosterControlled, Variable3Controlled, BrakeCylControlled, CurveForceControlled };
+        public enum Controls { None, DistanceControlled, SpeedControlled, Variable1Controlled, Variable1_2Controlled, Variable1_3Controlled, Variable1_4Controlled, Variable2Controlled, Variable2BoosterControlled, Variable3Controlled, BrakeCylControlled, CurveForceControlled, BackPressureControlled };
 
         public Controls Control = Controls.None;
         public float Granularity = 1.0f;
@@ -264,6 +264,7 @@ public VolumeCurve(STFReader stf)
                 case "variable3controlled": Control = Controls.Variable3Controlled; break;
                 case "brakecylcontrolled": Control = Controls.BrakeCylControlled; break;
                 case "curveforcecontrolled": Control = Controls.CurveForceControlled; break;
+                case "backpressurecontrolled": Control = Controls.BackPressureControlled; break;
                 default: STFException.TraceWarning(stf, "Crash expected: Skipped unknown VolumeCurve/Frequencycurve type " + type); stf.SkipRestOfBlock(); return;
             }
             stf.ParseBlock(new STFReader.TokenProcessor[] {

Source/Orts.Simulation/Simulation/RollingStocks/MSTSSteamLocomotive.cs

@@ -3192,6 +3192,9 @@ public override void Update(float elapsedClockSeconds)
 
             }
 
+            // calculate total back pressure from all exhausts
+            BackPressurePSIG = BackPressuretoSteamOutput[pS.TopH(CylinderSteamUsageLBpH)];
+
             UpdateTractiveForce(elapsedClockSeconds, ThrottlePercent / 100f, AbsSpeedMpS, AbsWheelSpeedMpS);
 
             #endregion

Source/Orts.Simulation/Simulation/RollingStocks/TrainCar.cs

@@ -1,4 +1,4 @@
-// COPYRIGHT 2009 - 2022 by the Open Rails project.
+// COPYRIGHT 2009 - 2022 by the Open Rails project.
 // 
 // This file is part of Open Rails.
 // 
@@ -183,6 +183,8 @@ public static Interpolator SteamHeatBoilerFuelUsageGalukpH()
         public float CarHeatCurrentCompartmentHeatJ;
         public float CarInsideTempC;
 
+        public float BackPressurePSIG; // Back pressure in steam cylinder for sound system
+
         // some properties of this car
         public float CarWidthM = 2.5f;
         public float CarLengthM = 40;       // derived classes must overwrite these defaults

Source/RunActivity/Viewer3D/Sound.cs

@@ -1504,6 +1504,7 @@ private float ReadValue(Orts.Formats.Msts.VolumeCurve.Controls control, MSTSWago
                 case Orts.Formats.Msts.VolumeCurve.Controls.Variable3Controlled: return car.Variable3;
                 case Orts.Formats.Msts.VolumeCurve.Controls.BrakeCylControlled: return car.BrakeSystem.GetCylPressurePSI();
                 case Orts.Formats.Msts.VolumeCurve.Controls.CurveForceControlled: return car.CurveForceNFiltered;
+                case Orts.Formats.Msts.VolumeCurve.Controls.BackPressureControlled: return car.BackPressurePSIG;
                 default: return 0;
             }
         }