From a8ba625bfa0060dd18df765ea3b05e3afbb642b3 Mon Sep 17 00:00:00 2001
From: Yuki Kitagawa <yuki.kitagawa@pm.me>
Date: Thu, 31 Oct 2024 22:46:27 +0800
Subject: [PATCH] Add krakensbane

---
 src/Craft/Krakensbane.cs | 51 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 src/Craft/Krakensbane.cs

diff --git a/src/Craft/Krakensbane.cs b/src/Craft/Krakensbane.cs
new file mode 100644
index 0000000..18f85f6
--- /dev/null
+++ b/src/Craft/Krakensbane.cs
@@ -0,0 +1,51 @@
+using System.Diagnostics;
+using Godot;
+
+namespace Quadratic.Carto.Craft;
+
+/// <summary>
+/// Krakensbane manages the position of its direct descendants, to ensure the
+/// focused vessel is not too far from the origin.
+/// </summary>
+/// <remarks>
+/// The name Krakensbane is a legacy of the original KSP module which does the 
+/// same thing, i.e. preventing floating point errors from causing the vessel
+/// to be thrown into deep space.
+/// </remarks>
+public sealed partial class Krakensbane : Node3D
+{
+    Node3D? focusedVessel = null;
+
+    const float maxDistance = 500.0f;
+
+    public override void _PhysicsProcess(double delta)
+    {
+        Debug.Assert(
+            focusedVessel == null || focusedVessel.GetParent() == this,
+            "Focused vessel must be a direct descendant of Krakensbane"
+        );
+
+        if (focusedVessel == null)
+        {
+            return;
+        }
+
+        var vesselPosition = focusedVessel.Transform.Origin;
+        var vesselDistance = vesselPosition.Length();
+        if (vesselDistance > maxDistance)
+        {
+            // Reset the vessel's position to the origin
+            // TODO: save the total offset; we don't yet have a double-precision vector3
+            var applyTransform = Transform3D.Identity.Translated(-vesselPosition);
+
+            int n_children = GetChildCount();
+            for (int i = 0; i < n_children; i++)
+            {
+                var child = GetChild<Node3D>(i);
+                child.Transform = applyTransform * child.Transform;
+            }
+
+            GD.Print($"Resetting position; delta = {-vesselPosition}");
+        }
+    }
+}