Focused nodes and focus owners

[John Hendrikx]

On 18/08/2023 18:35, Michael Strauß wrote:
> Scene graph nodes have three focus-related properties:
> 1. focused
> 2. focus-within
> 3. focus-visible
>
> What might be a bit surprising is that multiple nodes can be focused
> at the same time, but only one of those focused nodes can be the
> scene's focus owner. The `Scene.focusOwner` property indicates which
> of the focused nodes is the current focus owner.
>
> Even more surprisingly, a node can be _unfocused_  and be the focus
> owner at the same time (this can happen when the window is
> deactivated).
>
>  From the perspective of `Node`, there's currently no API to easily
> determine whether it is the focus owner, and there's no CSS
> pseudo-class that matches a node that is the focus owner.

Wouldn't `node.getScene().getFocusOwner() == node` do this?  Not for 
CSS, I agree.

I think it may be of benefit for my application. Focus for me is pretty 
useless as my application rarely has its Window focused -- the focus 
however is still visible and used (the application reacts to external 
commands given by remote control, no need for Window focus).  Using the 
`focused` pseudo class in stylesheets is pretty useless for me as 
whatever has focus won't show up when the main window doesn't have 
focus.  I've resorted to track the focus owner, and adding/removing a 
focused style class to the current focused node (and use the styleclass 
instead of the pseudo class in my stylesheets) -- this was before I knew 
you can also easily add a new pseudo class to a node, but a styleclass 
works fine for this purpose.

This potential new pseudo class (focus-owner) would have been a good 
alternative for me, although I will immediately admit that it probably 
is of very limited use for other applications.

There is also the internal-focus and external-focus pseudo classes for 
those of us using the TwoLevelFocusBehavior (especially useful for apps 
controlled by remote with limited keys to interact with controls).  I 
believe it may be removed in the future though, at least there is a 
ticket for that (unresolved).

--John

>
> We could add two more properties to the `Node` class to support this use case:
> 4. focus-owner
> 5. focus-owner-within
>
> Note that `focus-visible` only matches nodes that are also focus
> owners, so there's no need to have a `focus-owner-visible` property.
>
> The two additional properties would suffice to match any possible
> focus state, but it might also be not useful enough to warrant the
> additional API surface. What do you think?