RFR: 8365637: Unmanaged nodes are not added to the Scene's dirty layout list

[Alessadro Parisi]

On Mon, 18 Aug 2025 18:00:39 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

> > If the node is unmanaged, why does it need a relayout in practice?
> 
> The unmanaged node does not need relayout, but its potentially managed children do. Just like a Scene does not need layout, but its root does. A node being unmanaged affects its **parent** (the parent must skip it for layout calculations), but does not free it from doing layout on its own children (if I interpret the documentation correctly).
> 
> Let's take this hierarchy:
> 
> ```
> Region
>      StackPane (unmanaged)
>            ImageView
> ```
> 
> The Region will not lay out the stack pane as it is unmanaged, so I position the unmanaged child manually with `resizeRelocate`. The StackPane now has a defined position and size. When I add children to it, the StackPane's `layout` (and conversely `layoutChildren`) should still be called to ensure the children nicely fill the StackPane's space.
> 
> JavaFX currently will do steps 1 and 2, but does not do step 3:
> 
>     1. Another child is added to the StackPane (an overlay for the ImageView) this triggers a requestLayout on that child which marks it as needing layout
> 
>     2. This propagates to the parent, which is also marked as needing layout, but it is considered to be a layout root, so no further propagation occurs
> 
>     3. Since a layout root was encountered, it should be added to the list of dirty layout roots (implemented in this PR).  This will clear all the needs layout flags (otherwise they stay `true` and never go back to `false` again).
> 
> 
> The documentation however seems quite clear that step 3 is also supposed to be done.

So, as of now unmanaged parents do not layout their children? I thought they did.

<img width="1346" height="924" alt="immagine" src="https://github.com/user-attachments/assets/a1e3c93c-7855-4591-a8df-504d48f6da60" />
Am I getting something wrong?

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PR Comment: https://git.openjdk.org/jfx/pull/1874#issuecomment-3213393789