OrbitParentTool - a Unity EditorTool to orbit selected objects around their parents (my first test with EditorTools)

OrbitParentTool.cs

using UnityEngine;
using UnityEditor;
using UnityEditor.EditorTools;

[EditorTool("Orbit Parent Tool", typeof(Transform))]
class OrbitParentTool : EditorTool
{
    [SerializeField]
    private Texture2D _toolIcon;

    private GUIContent _iconContent;

    public override GUIContent toolbarIcon => _iconContent;

    private void OnEnable()
    {
        _iconContent = new GUIContent()
        {
            image = _toolIcon,
            text = "Orbit Parent Tool",
            tooltip = "Orbit selected objects around their parents"
        };
    }

    // This is called for each window that your tool is active in. Put the functionality of your tool here.
    public override void OnToolGUI(EditorWindow window)
    {
        if (Selection.activeTransform == null)
        {
            return;
        }

        var didUserInput = DrawAllHandles(out var deltaHandleRotation);

        if (didUserInput)
        {
            Undo.RecordObjects(Selection.transforms, "Orbit Parent");

            foreach (var transform in Selection.transforms)
            {
                OrbitAroundParent(transform, deltaHandleRotation);
            }
        }
    }

    private bool DrawAllHandles(out Quaternion deltaHandleRotation)
    {
        var didUserInput = false;
        deltaHandleRotation = Quaternion.identity;

        foreach (var t in Selection.transforms)
        {
            var parentPos = t.parent.position;
            var fromParent = t.position - parentPos;
            var fromParentDir = fromParent.normalized;
            float orbitDistance = Vector3.Dot(fromParentDir, fromParent);

            if (Mathf.Approximately(orbitDistance, 0))
            {
                continue;
            }

            var handleDir = Vector3.Cross(fromParentDir, Vector3.forward);
            var reconstructedForwardVector = Vector3.Cross(fromParentDir, handleDir);

            var rotFromParent = Quaternion.LookRotation(fromParentDir, handleDir);
            var oldHandleRotation = rotFromParent;
            var newHandleRotation = rotFromParent;

            EditorGUI.BeginChangeCheck();
            using (new Handles.DrawingScope(Color.green))
            {
                newHandleRotation = Handles.RotationHandle(oldHandleRotation, parentPos);
                Handles.DrawWireArc(parentPos, reconstructedForwardVector, fromParentDir, 45, orbitDistance);
            }

            if (EditorGUI.EndChangeCheck())
            {
                deltaHandleRotation = newHandleRotation * Quaternion.Inverse(oldHandleRotation);
                didUserInput = true;
            }
        }

        return didUserInput;
    }

    private bool DrawAllHandles__(out Quaternion deltaHandleRotation)
    {
        deltaHandleRotation = Quaternion.identity;

        var t = Selection.activeTransform;
        var parentPos = t.parent.position;
        var fromParent = t.position - parentPos;
        var fromParentDir = fromParent.normalized;
        float orbitDistance = Vector3.Dot(fromParentDir, fromParent);

        if (Mathf.Approximately(orbitDistance, 0))
        {
            return false;
        }

        var handleDir = Vector3.Cross(fromParentDir, Vector3.forward);
        var reconstructedForwardVector = Vector3.Cross(fromParentDir, handleDir);

        var rotFromParent = Quaternion.LookRotation(fromParentDir, handleDir);
        var oldHandleRotation = rotFromParent;
        var newHandleRotation = rotFromParent;

        EditorGUI.BeginChangeCheck();
        using (new Handles.DrawingScope(Color.green))
        {
            newHandleRotation = Handles.RotationHandle(oldHandleRotation, parentPos);
            Handles.DrawWireArc(parentPos, reconstructedForwardVector, fromParentDir, 45, orbitDistance);
        }

        if (EditorGUI.EndChangeCheck())
        {
            deltaHandleRotation = newHandleRotation * Quaternion.Inverse(oldHandleRotation);
            return true;
        }

        return false;
    }

    private void OrbitAroundParent(Transform t, Quaternion deltaRotation)
    {
        var parentPos = t.parent.position;
        var fromParent = t.position - parentPos;
        var rotatedFromParent = deltaRotation * fromParent;
        t.position = parentPos + rotatedFromParent;
    }
}