Quick and dirty Unity tool to place an object

PlaceObjectTool.cs

using UnityEditor;
using UnityEditor.EditorTools;
using UnityEditor.UIElements;
using UnityEngine;
using UnityEngine.UIElements;

[EditorTool("Place Object Tool")]
public class PlaceObjectTool : EditorTool
{
    [SerializeField] Texture2D m_ToolIcon;

    GUIContent m_IconContent;

    VisualElement toolRootElement;
    Toggle useCurrentSelection;
    ObjectField prefabObjectField;

    bool receivedClickDownEvent;
    bool receivedClickUpEvent;

    public override GUIContent toolbarIcon => m_IconContent;

    public override void OnActivated()
    {
        m_IconContent = new GUIContent
        {
            image = m_ToolIcon,
            text = "Place Object Tool",
            tooltip = "Place Object Tool"
        };

        var sv = SceneView.lastActiveSceneView;
        SceneView.beforeSceneGui += BeforeSceneGUI;
        toolRootElement = new VisualElement();
        toolRootElement.style.width = 200;
        var titleLabel = new Label("Place Object Tool");
        toolRootElement.Add(titleLabel);

        prefabObjectField = new ObjectField {allowSceneObjects = true, objectType = typeof(GameObject)};
        useCurrentSelection = new Toggle {label = "Use Current Selection"};
        useCurrentSelection.RegisterValueChangedCallback(evt => { prefabObjectField.visible = !evt.newValue; });

        toolRootElement.Add(useCurrentSelection);
        toolRootElement.Add(prefabObjectField);
        sv.rootVisualElement.Add(toolRootElement);
        sv.rootVisualElement.style.flexDirection = FlexDirection.ColumnReverse;
    }

    public override void OnWillBeDeactivated()
    {
        SceneView.beforeSceneGui -= BeforeSceneGUI;
        toolRootElement?.RemoveFromHierarchy();
    }

    public void BeforeSceneGUI(SceneView sceneView)
    {
        if (ToolManager.IsActiveTool(this))
        {
            if (useCurrentSelection.value && Selection.activeGameObject == null)
            {
                receivedClickDownEvent = false;
                receivedClickUpEvent = false;
                return;
            }

            if (!useCurrentSelection.value && prefabObjectField?.value == null)
            {
                receivedClickDownEvent = false;
                receivedClickUpEvent = false;
                return;
            }

            if (Event.current.type == EventType.MouseDown && Event.current.button == 0)
            {
                receivedClickDownEvent = true;
                Event.current.Use();
            }

            if (receivedClickDownEvent && Event.current.type == EventType.MouseUp && Event.current.button == 0)
            {
                receivedClickDownEvent = false;
                receivedClickUpEvent = true;
                Event.current.Use();
            }
        }
    }

    public override void OnToolGUI(EditorWindow window)
    {
        if (!(window is SceneView sceneView))
            return;


        if (ToolManager.IsActiveTool(this))
        {
            if (useCurrentSelection.value && Selection.activeGameObject == null)
            {
                return;
            }

            if (!useCurrentSelection.value && prefabObjectField?.value == null)
            {
                return;
            }

            Handles.DrawWireDisc(GetCurrentMousePositionInScene(), Vector3.up, 1f);
            if (receivedClickUpEvent)
            {
                var newObject = useCurrentSelection.value ? Selection.activeGameObject : prefabObjectField.value;

                PrefabUtility.IsPartOfPrefabInstance(newObject);
                var newPrefabInstance = (GameObject) PrefabUtility.InstantiatePrefab(newObject);
                if (newPrefabInstance == null)
                {
                    if (PrefabUtility.IsPartOfPrefabInstance(newObject))
                    {
                        var prefabPath = PrefabUtility.GetPrefabAssetPathOfNearestInstanceRoot(newObject);
                        var prefab = AssetDatabase.LoadAssetAtPath<GameObject>(prefabPath);
                        newPrefabInstance = (GameObject) PrefabUtility.InstantiatePrefab(prefab);
                    }
                    else
                    {
                        newPrefabInstance = Instantiate((GameObject) newObject);
                    }
                }

                newPrefabInstance.transform.position = GetCurrentMousePositionInScene();

                Event.current.Use();
                Undo.RegisterCreatedObjectUndo(newPrefabInstance, "Place new object");
                receivedClickUpEvent = false;
            }
        }
    }

    Vector3 GetCurrentMousePositionInScene()
    {
        Vector3 mousePosition = Event.current.mousePosition;
        var placeObject = HandleUtility.PlaceObject(mousePosition, out var newPosition, out var normal);
        return placeObject ? newPosition : HandleUtility.GUIPointToWorldRay(mousePosition).GetPoint(10);
    }
}