// About the position hanlde see example https://docs.unity3d.com/ScriptReference/Handles.PositionHandle.html
        public void OnSceneGUI()
        {
            int controlId = GUIUtility.GetControlID(GetHashCode(), FocusType.Passive);

            Ray        ray = HandleUtility.GUIPointToWorldRay(Event.current.mousePosition);
            RaycastHit hit;



            if (Physics.Raycast(ray.origin, ray.direction, out hit, Mathf.Infinity))
            {
                mousePos      = hit.point;
                mousePosValid = true;

                ///
                /// process mouse & keyboard events
                ///

                //if (EditorWindow.focusedWindow)
                {
                    switch (Event.current.type)
                    {
                    case EventType.KeyDown:
                    {
                        // toggle add mode
                        if (Event.current.shift && Event.current.keyCode == KeyCode.A)
                        {
                            // toggle add mode

                            SplineSettings.AttachMode selectedAttachMode = gizmo.splineSettings.attachMode;

                            /*
                             * SplineSettings.AttachMode selectedAttachMode = (SplineSettings.AttachMode)System.Enum.GetValues(typeof(SplineSettings.AttachMode)).GetValue(attachMode.enumValueIndex);
                             *
                             * int boundsIndex = ArrayUtility.IndexOf((SplineSettings.AttachMode[])System.Enum.GetValues(typeof(SplineSettings.AttachMode)), SplineSettings.AttachMode.Bounds);
                             * int betweenIndex = ArrayUtility.IndexOf((SplineSettings.AttachMode[])System.Enum.GetValues(typeof(SplineSettings.AttachMode)), SplineSettings.AttachMode.Between);
                             */

                            if (selectedAttachMode == SplineSettings.AttachMode.Bounds)
                            {
                                gizmo.splineSettings.attachMode = SplineSettings.AttachMode.Between;
                            }
                            else
                            {
                                gizmo.splineSettings.attachMode = SplineSettings.AttachMode.Bounds;
                            }

                            // trigger repaint, so that the enumpopup will be updated
                            editor.Repaint();
                        }
                        ;

                        break;
                    }
                    }
                }

                // control key pressed
                if (Event.current.shift)
                {
                    mousePos      = hit.point;
                    mousePosValid = true;

                    // shift + ctrl = delete
                    bool deleteMode = Event.current.control;

                    int addControlPointIndex = FindClosestControlPoint(mousePos);

                    //Handles.DrawSphere(controlId, mousePos, Quaternion.identity, 0.3f);
                    Color handleColor;
                    if (deleteMode)
                    {
                        handleColor = Color.red; // red = delete
                    }
                    // draw attachment line
                    else
                    {
                        handleColor = Color.gray; // gray = add
                    }

                    // draw gray circle
                    float radius = 0.1f;
                    Handles.color = handleColor;
                    Handles.DrawWireDisc(mousePos, hit.normal, radius);

                    // draw line to closest point
                    if (gizmo.splineSettings.controlPoints.Count > 0)
                    {
                        // draw indicator line to closest control point
                        Vector3 lineStartPosition = gizmo.splineSettings.controlPoints.ElementAt(addControlPointIndex).position;
                        Vector3 lineEndPosition   = mousePos;

                        Handles.DrawLine(lineStartPosition, lineEndPosition);

                        // draw additional indicator line to the control point which is next in the list after the closest control point
                        if (!deleteMode)
                        {
                            int neighbourIndex;
                            if (addControlPointIndex > 0)
                            {
                                neighbourIndex = addControlPointIndex - 1;
                            }
                            else
                            {
                                neighbourIndex = addControlPointIndex + 1;
                            }

                            if (gizmo.splineSettings.attachMode == SplineSettings.AttachMode.Between && neighbourIndex >= 0 && neighbourIndex <= gizmo.splineSettings.controlPoints.Count - 1)
                            {
                                Vector3 neighbourLineStartPosition = gizmo.splineSettings.controlPoints.ElementAt(neighbourIndex).position;
                                Vector3 neighbourLineEndPosition   = mousePos;

                                Handles.DrawLine(neighbourLineStartPosition, neighbourLineEndPosition);
                            }
                        }
                    }

                    if (Event.current.type == EventType.MouseDown)
                    {
                        // delete node
                        if (deleteMode)
                        {
                            bool canDelete = gizmo.splineSettings.controlPoints.Count > 0;

                            if (Event.current.button == 0 && canDelete)
                            {
                                Vector3 mousePosition = new Vector3(mousePos.x, mousePos.y, mousePos.z);

                                int controlPointIndex = FindClosestControlPoint(mousePosition);

                                // remove the closest point
                                if (controlPointIndex != -1)
                                {
                                    RemoveControlPoint(controlPointIndex);
                                }


                                Event.current.Use();
                            }
                        }
                        // add new node
                        else
                        {
                            // left button = 0; right = 1; middle = 2
                            if (Event.current.button == 0)
                            {
                                Vector3 position = new Vector3(mousePos.x, mousePos.y, mousePos.z);

                                AddControlPoint(position, addControlPointIndex);

                                Event.current.Use();
                            }
                        }
                    }
                }
            }
            else
            {
                mousePosValid = false;
            }

            if (Event.current.type == EventType.Layout)
            {
                HandleUtility.AddDefaultControl(controlId);
            }

            DrawSplineGizmos();

            // create gameobjects
            if (mousePosValid)
            {
                PerformEditorAction();
            }


            // show info
            Handles.BeginGUI();

            string[] info = new string[] { "Add Control Point: shift + click", "Remove control point: shift + ctrl + click", "Change Attach Mode: shift + A, Current: " + gizmo.splineSettings.attachMode };
            PrefabPainterEditor.ShowGuiInfo(info);

            Handles.EndGUI();
        }