How to keep multiple editor tool enabled at once in Unity GUI?

Question

I have created a simple custom editor tool, which allows me to keep mouse position in a straight line. I require this to draw texture on a terrain in a straight line. Unfortunately, when I enable "Paint texture" tool in the terrain editor in inspector, my custom tool gets disabled and vice-versa. How can I keep both my custom tool and terrain paint tool enabled at once?

Custom tool selected but paint texture is deactivated-

Custom tool got deselected on paint texture selection-

Following is the OnToolGUI method

    public override void OnToolGUI(EditorWindow window)
    {
        HandleUtility.AddDefaultControl(GUIUtility.GetControlID(FocusType.Passive));
        Event e = Event.current;
        if (!(window is SceneView))
            return;

        if (!ToolManager.IsActiveTool(this))
            return;

        if (e.shift)
        {
            if (e.type == EventType.MouseDown)
            {
                if (e.button == 0)
                {
                    downY = e.mousePosition.y;
                }
            }
            if (e.type == EventType.MouseDrag)
            {
                if (e.button == 0)
                {
                    e.mousePosition = new Vector2(e.mousePosition.x, downY);
                    Debug.Log("Mouse Position: " + e.mousePosition);
                }
            }
        }

Answer 1

As mentioned in the comments I guess it simply is the nature of the tools that they are exclusive and you can only have one active at a time.

As alternative I would rather simply

• enable/disable this via a general header menu entry
• (optionally) store that decision persistent in EditorPrefs (pretty much like PlayerPrefs but for the editor itself)
• and accordingly attach a listener to SceneView.duringSceneGui

This could look somewhat like e.g.

public static class StraightLineTool
{
    // Used for the displayed menu labels 
    // and also simply (ab)used as the unique key for the EditorPrefs
    private const string k_MenuName = "My Tools/Straight Line Tool";

    private static float downY;

    // Property for simplifying access and setting more centralized
    private static bool IsEnabled
    {
        get => EditorPrefs.GetBool(k_MenuName, false);
        set => EditorPrefs.SetBool(k_MenuName, value);
    }

    // method to be called when clicking the menu button
    [MenuItem(k_MenuName)]
    private static void ToggleEnabled()
    {
        IsEnabled = !IsEnabled;

        ApplySettings();
    }

    // adding a checkmark when is enabled and simply always allow to click it
    [MenuItem(k_MenuName, true)]
    private static bool ToggleEnabledValidate()
    {
        Menu.SetChecked(k_MenuName, IsEnabled);
        return true;
    }

    // Called on every project loading or code recompilation
    [InitializeOnLoadMethod]
    private static void Initialize()
    {
        EditorApplication.delayCall -= ApplySettings;
        EditorApplication.delayCall += ApplySettings;
    }

    private static void ApplySettings()
    {
        // remove so only happening once
        EditorApplication.delayCall -= ApplySettings;

        SceneView.duringSceneGui -= OnSceneGUI;

        if (IsEnabled)
        {
            // if enabled start listening
            SceneView.duringSceneGui += OnSceneGUI;
        }
    }

    // Callback listening to any SceneView.duringSceneGui
    private static void OnSceneGUI(SceneView sceneView)
    {
        // Not sure tbh what this does or if you need it still in this approach
        // HandleUtility.AddDefaultControl(GUIUtility.GetControlID(FocusType.Passive));
        var currentEvent = Event.current;

        if (currentEvent.shift)
        {
            if (currentEvent.type == EventType.MouseDown)
            {
                if (currentEvent.button == 0)
                {
                    downY = currentEvent.mousePosition.y;
                }
            }

            if (currentEvent.type == EventType.MouseDrag)
            {
                if (currentEvent.button == 0)
                {
                    currentEvent.mousePosition = new Vector2(currentEvent.mousePosition.x, downY);
                    Debug.Log("Mouse Position: " + currentEvent.mousePosition);
                }
            }
        }
    }
}

=> using this the tool will be enabled/disabled persistent even when restarting Unity

---

Then using this as start point you can probably still try to somehow integrate this somewhere more nicely into the SceneView menus - but maybe that is also overkill ;)