On Mon, 18 Aug 2025 17:01:59 GMT, Nir Lisker <nlis...@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.
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PR Comment: https://git.openjdk.org/jfx/pull/1874#issuecomment-3197898264
