carto-revive/src/Craft/Krakensbane.cs

using System.Diagnostics;
using Godot;
using ImGuiNET;
using Quadratic.Carto.MathExt;

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
{
    [Export]
    public Node3D? FocusedVessel { get; set; }

    const float maxDistance = 500.0f;

    DVector3 originPosition = DVector3.Zero;

    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;
            }

            originPosition += vesselPosition.AsVim().AsDouble();
        }
    }

    public override void _Process(double delta)
    {
        ImGui.Begin("Krakensbane");
        ImGui.Text($"Origin: {originPosition}");
        ImGui.End();
    }
}