Zero residuals before doing RCS calcs

ModuleRCS doesn't have residuals and this was causing infinite spinning.

Note that it makes me worried there's some sort of floating point round
off error bug inherent to residuals, because it should have at least
worked and gotten the wrong answer.

Signed-off-by: Lamont Granquist <lamont@scriptkiddie.org>

MechJeb2/MechJebLib/Simulations/FuelFlowSimulation.cs

@@ -36,6 +36,7 @@ protected override bool Run(object? o)
             while (vessel.CurrentStage >= 0) // FIXME: should stop mutating vessel.CurrentStage
             {
                 SimulateStage(vessel);
+                ClearResiduals(vessel);
                 ComputeRcsMaxValues(vessel);
                 FinishSegment(vessel);
                 vessel.Stage();
@@ -96,10 +97,11 @@ private void SimulateStage(SimVessel vessel)
             vessel.UpdateMass();
             vessel.UpdateEngineStats();
             vessel.UpdateActiveEngines();
-            UpdateResourceDrainsAndResiduals(vessel);
 
             GetNextSegment(vessel);
             ComputeRcsMinValues(vessel);
+
+            UpdateResourceDrainsAndResiduals(vessel);
             double currentThrust = vessel.ThrustMagnitude;
 
             for (int steps = MAXSTEPS; steps > 0; steps--)
@@ -113,6 +115,7 @@ private void SimulateStage(SimVessel vessel)
                 // prior > 0dV segment in the same kspStage we should add those together to reduce clutter.
                 if (Math.Abs(vessel.ThrustMagnitude - currentThrust) > 1e-12)
                 {
+                    ClearResiduals(vessel);
                     ComputeRcsMaxValues(vessel);
                     FinishSegment(vessel);
                     GetNextSegment(vessel);
@@ -234,6 +237,12 @@ private void UpdateRCSDrainsInPart(SimPart p, double resourceConsumption, int re
             p.AddRCSDrain(resourceId, resourceConsumption);
         }
 
+        private void ClearResiduals(SimVessel vessel)
+        {
+            foreach (SimPart part in _partsWithResourceDrains)
+                part.ClearResiduals();
+        }
+
         private void UpdateResourceDrainsAndResiduals(SimVessel vessel)
         {
             foreach (SimPart part in _partsWithResourceDrains)

MechJeb2/MechJebLib/Simulations/SimPart.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Text;
 using MechJebLib.Utils;
+using static MechJebLib.Utils.Statics;
 
 namespace MechJebLib.Simulations
 {
@@ -131,6 +132,20 @@ public void UpdateResourceResidual(double residual, int resourceId)
             Resources[resourceId] = resource;
         }
 
+        public void ClearResiduals()
+        {
+            _resourceKeys.Clear();
+            foreach (int id in Resources.Keys)
+                _resourceKeys.Add(id);
+
+            foreach (int id in _resourceKeys)
+            {
+                SimResource resource = Resources[id];
+                resource.Residual = 0;
+                Resources[id] = resource;
+            }
+        }
+
         public double ResidualThreshold(int resourceId) => Resources[resourceId].ResidualThreshold + ResourceRequestRemainingThreshold;
 
         public void ClearResourceDrains() => _resourceDrains.Clear();

MechJeb2/MechJebLib/Simulations/SimResource.cs

@@ -26,14 +26,17 @@ public double Amount
         public SimResource Drain(double resourceDrain)
         {
             _amount -= resourceDrain;
-            if (_amount < 0) _amount = 0;
+            if (_amount < 0)
+                _amount = 0;
+
             return this;
         }
 
         public SimResource RCSDrain(double rcsDrain)
         {
             _rcsAmount -= rcsDrain;
-            if (Amount < 0) _rcsAmount = _amount;
+            if (Amount < 0)
+                _rcsAmount = _amount;
 
             return this;
         }