Fall back to an uncrewed control source on vessel separation

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ##### Unreleased
 **New/Improved patches**
+- New KSP bugfix : **UncrewedControlPointFallback** Fix a vessel created by decoupling, undocking or a part being destroyed getting no control point unless it carries a part with a kerbal aboard, leaving the navball, SAS and autopilots oriented by its root part. An uncrewed control source (probe core, empty command pod...) is now used as a fallback.
 - Improved the **FastLoader** patch to reuse the initial GameDatabase directory tree during the second config pass while refreshing files and directories created or modified by `Startup.Instantly` addons. Avoids reparsing unchanged configs and saves several seconds in heavily modded installs.
 
 **Bug Fixes**

GameData/KSPCommunityFixes/Settings.cfg

@@ -283,6 +283,11 @@ KSP_COMMUNITY_FIXES
   // dialog being wildly inflated.
   FlightLoggerInflatedDistance = true
 
+  // Fix a vessel created by decoupling, undocking or a part being destroyed getting no control point
+  // unless it carries a part with a kerbal aboard, leaving it oriented by its root part instead. An
+  // uncrewed control source (a probe core, an empty command pod...) is now used as a fallback.
+  UncrewedControlPointFallback = true
+
   // ##########################
   // Obsolete bugfixes
   // ##########################

KSPCommunityFixes/BugFixes/UncrewedControlPointFallback.cs

@@ -0,0 +1,74 @@
+// When a vessel is split off another one (decoupling, undocking, a part being destroyed) or loaded
+// without a valid reference transform, Vessel.FallBackReferenceTransform() is responsible for picking
+// a control point for it. It delegates that choice to ShipConstruction.findFirstCrewablePart() :
+//
+//   public void FallBackReferenceTransform()
+//   {
+//       if (this[referenceTransformId] == null)
+//           SetReferenceTransform(ShipConstruction.findFirstCrewablePart(rootPart), true);
+//   }
+//
+//   public static Part findFirstCrewablePart(Part part)
+//   {
+//       if (part.CrewCapacity > 0 && part.protoModuleCrew.Count > 0 && part.isControlSource > Vessel.ControlLevel.NONE)
+//           return part;
+//       ...recurse over part.children...
+//   }
+//
+// findFirstCrewablePart() answers a different question than the one being asked : it looks for a part a
+// kerbal is sitting in and can fly the vessel from, which is what its other callers (crew transfer, vessel
+// spawning) want. A probe core fails the crew capacity test outright, and an empty command pod fails the
+// "crew aboard" test, so an uncrewed vessel gets no control point at all : SetReferenceTransform(null, true)
+// resets referenceTransformId to 0 and referenceTransformPart to null, and the vessel is then oriented by
+// its root part. Every navball reading, SAS hold and autopilot attitude on that vessel is taken from
+// whatever the root part happens to be, until the player manually picks a control point.
+//
+// We reimplement FallBackReferenceTransform() so that when findFirstCrewablePart() comes up empty, it falls
+// back to the first part that is a control source, searched in the same root-first order. A crewed part
+// still wins, matching how KSP ranks a kerbal above a probe core elsewhere in its control state handling.
+// findFirstCrewablePart() itself is left alone, as its other callers want its existing meaning.
+
+using System;
+using System.Collections.Generic;
+
+namespace KSPCommunityFixes.BugFixes;
+
+internal class UncrewedControlPointFallback : BasePatch
+{
+    protected override Version VersionMin => new(1, 8, 0);
+
+    protected override void ApplyPatches()
+    {
+        AddPatch(PatchType.Override, typeof(Vessel), nameof(Vessel.FallBackReferenceTransform));
+    }
+
+    private static void Vessel_FallBackReferenceTransform_Override(Vessel __instance)
+    {
+        if (__instance[__instance.referenceTransformId].IsNotNullOrDestroyed())
+            return;
+
+        Part referencePart = ShipConstruction.findFirstCrewablePart(__instance.rootPart);
+
+        // This is the part we are actually intending to patch : stock passes the null straight through.
+        if (referencePart.IsNullOrDestroyed())
+            referencePart = FindFirstControlSourcePart(__instance.rootPart);
+
+        __instance.SetReferenceTransform(referencePart, true);
+    }
+
+    private static Part FindFirstControlSourcePart(Part part)
+    {
+        if (part.isControlSource > Vessel.ControlLevel.NONE)
+            return part;
+
+        List<Part> children = part.children;
+        for (int i = 0; i < children.Count; i++)
+        {
+            Part controlSource = FindFirstControlSourcePart(children[i]);
+            if (controlSource.IsNotNullOrDestroyed())
+                return controlSource;
+        }
+
+        return null;
+    }
+}

README.md

@@ -106,6 +106,7 @@ User options are available from the "ESC" in-game settings menu :<br/><img src="
 - [**FIUpdateRadiation**](https://github.com/KSPModdingLibs/KSPCommunityFixes/pull/364) [KSP 1.12.0 - 1.12.5]<br/>Fix radiation flux being inconsistent for timewarp rates between 1x and 100x, caused by `PartThermalData.expFlux` / `unexpFlux` being mutated during every thermal integration pass.
 - [**EditorAnimatedPartsShipModified**](https://github.com/KSPModdingLibs/KSPCommunityFixes/issues/388) [KSP 1.12.0 - 1.12.5]<br/>Fix the Engineer's Report craft dimensions (and other `onEditorShipModified` consumers) lagging one vessel modification behind when an animated part is actuated in the editor (deployable solar panels/radiators/antennas, `ModuleAnimateGeneric` animations, Breaking Ground robotic servos), by re-firing the modification event once the animation has actually finished.
 - [**FlightLoggerInflatedDistance**](https://github.com/KSPModdingLibs/KSPCommunityFixes/pull/402) [KSP 1.12.0 - 1.12.5]<br/>Fix the "distance travelled" / "distance over ground" values shown in the F3 flight results dialog being wildly inflated.
+- **UncrewedControlPointFallback** [KSP 1.8.0 - 1.12.5]<br/>Fix a vessel created by decoupling, undocking or a part being destroyed getting no control point unless it carries a part with a kerbal aboard, leaving the navball, SAS and autopilots oriented by its root part. `Vessel.FallBackReferenceTransform()` now falls back to the first uncrewed control source (probe core, empty command pod...) when `ShipConstruction.findFirstCrewablePart()` finds nothing.
 - **PartTooltipUpgradesApplyToSubstituteParts** [KSP 1.12.0 - 1.12.5]<br/>Disabled by default, you can enable it with a MM patch. Fix part upgrades being applied directly to the prefab part when creating the `PartListTooltip`, instead using a substitute part instance. Requires **UpgradeBugs** to be enabled.
 
 #### Quality of Life tweaks