Discussion Thoughts on the UI Toolkit focusing algorithm. Can we change it?

I was struggling a bit to understand how the focusing alogrithm works. I does not yield very good results (at least in my tests).

Let's assume this situation:

I wondered why the algorithm was unable to focus the other button. So I dove into the UI source code and found this:

Code (csharp):

1.  
2. Rect panelBounds = m_Root.worldBoundingBox;
3. Rect panelRect = new Rect(panelBounds.position - Vector2.one, panelBounds.size + Vector2.one * 2);
4. Rect rect = ve.worldBound;
5. Rect validRect = new Rect(rect.position - Vector2.one, rect.size + Vector2.one * 2);
6. if (direction == Up) validRect.yMin = panelRect.yMin;
7. else if (direction == Down) validRect.yMax = panelRect.yMax;
8. else if (direction == Left) validRect.xMin = panelRect.xMin;
9. else if (direction == Right) validRect.xMax = panelRect.xMax;
10.  

Here is what that code does:


If you want to make a game ui that supports gamepad and keyboard input this is bad news. Users may get stuck if there is no overlapping focusable element in one of the four directions.

Another issue I have with the algorithm is that is uses only the children inside the "contentContainer".
Usually that is fine but there are some Unity Controls (like the ScrollView) that put elements outside the contentContainer (they override the contentContainer) and thus effectively make their controls inaccessible via keyboard or gamepad. You can focus them with the mouse or TAB but that is hard to explain to console players ;-)

I don't think that contentContainer overrides were an accident. I think that's by design. Though, I do not like the focusing side-effects it has.

Does anyone know if we can inject a custom focus traversal method?

 

Sadly tabbing is not a good option for console players. AFAIK there is no default button assigned to "tab" on a controller (tried on xbox).

Thanks. I was hoping for another solution. What I do now is intercept at the Control root level and do my own focusable discovery (or rather I make elements temporarily focusable to trigger the behaviour I want).