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feat: late-added UI siblings render on top (matching Unity) #693

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feat: late-added UI siblings render on top (matching Unity) #693

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101 changes: 76 additions & 25 deletions crates/scene_runner/src/update_world/scene_ui/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ pub mod ui_text;
use std::collections::{BTreeSet, VecDeque};

use bevy::{
diagnostic::FrameCount,
math::FloatOrd,
platform::collections::{HashMap, HashSet},
prelude::*,
Expand Down Expand Up @@ -59,6 +60,13 @@ use super::AddCrdtInterfaceExt;

pub struct SceneUiPlugin;

/// Stamps scene UI entities with the frame they were first created.
/// Used to sort siblings so that late-added entities render on top,
/// matching Unity's behaviour. Modifications to existing entities
/// do not reset this value.
#[derive(Component, Debug, Clone, Copy)]
pub struct UiCreationOrder(pub u32);

#[derive(Debug, Copy, Clone)]
struct Size {
width: Val,
Expand Down Expand Up @@ -773,7 +781,13 @@ fn layout_scene_ui(
mut scene_uis: Query<(Entity, &mut SceneUiData)>,
player: Query<Entity, With<PrimaryUser>>,
containing_scene: ContainingScene,
ui_nodes: Query<(&SceneEntity, Ref<UiTransform>, &ChildOf)>,
ui_nodes: Query<(
&SceneEntity,
Ref<UiTransform>,
&ChildOf,
Option<&UiCreationOrder>,
)>,
frame_count: Res<FrameCount>,
config: Res<AppConfig>,
mut removed_transforms: RemovedComponents<UiTransform>,
ui_links: Query<&UiLink>,
Expand Down Expand Up @@ -809,20 +823,25 @@ fn layout_scene_ui(

// collect ui data
let mut deleted_nodes = HashSet::new();
let current_frame = frame_count.0;
let mut unprocessed_uis = ui_data
.nodes
.iter()
.flat_map(|node| {
match ui_nodes.get(*node) {
Ok((scene_entity, transform, bevy_parent)) => Some((
scene_entity.id,
(
*node,
transform.clone(),
transform.is_changed(),
bevy_parent.parent(),
),
)),
Ok((scene_entity, transform, bevy_parent, creation_order)) => {
let creation_frame = creation_order.map(|c| c.0).unwrap_or(current_frame);
Some((
scene_entity.id,
(
*node,
transform.clone(),
transform.is_changed(),
bevy_parent.parent(),
creation_frame,
),
))
}
Err(_) => {
// remove this node
deleted_nodes.insert(*node);
Expand All @@ -831,7 +850,15 @@ fn layout_scene_ui(
}
})
.collect::<Vec<_>>();
unprocessed_uis.sort_by_key(|(scene_id, _)| *scene_id);
// Sort by creation frame first (late-added entities render on top),
// then by scene_id to preserve rightOf ordering within the same frame.
unprocessed_uis
.sort_by_key(|(scene_id, (_, _, _, _, creation_frame))| (*creation_frame, *scene_id));
// Map scene entity IDs to their creation frame for rightOf checks.
let creation_frames: HashMap<SceneEntityId, u32> = unprocessed_uis
.iter()
.map(|(scene_id, (_, _, _, _, creation_frame))| (*scene_id, *creation_frame))
.collect();
let mut unprocessed_uis: VecDeque<_> = unprocessed_uis.into();

let mut valid_nodes = HashMap::new();
Expand All @@ -841,29 +868,45 @@ fn layout_scene_ui(

let mut blocked_elements: HashMap<
SceneEntityId,
Vec<(SceneEntityId, (Entity, UiTransform, bool, Entity))>,
Vec<(SceneEntityId, (Entity, UiTransform, bool, Entity, u32))>,
> = HashMap::new();

while let Some((scene_id, (bevy_entity, ui_transform, transform_is_changed, root_node))) =
unprocessed_uis.pop_front()
while let Some((
scene_id,
(bevy_entity, ui_transform, transform_is_changed, root_node, creation_frame),
)) = unprocessed_uis.pop_front()
{
let Ok(bevy_ui_root) = ui_links.get(root_node).cloned() else {
warn!("no root for {:?}", root_node);
continue;
};

// if our rightof is not added, we can't process this node
// if our rightof is not added, we can't process this node —
// unless the rightof target was created in a later frame, in which
// case we skip the dependency so that late-added entities render on
// top rather than reordering existing siblings.
if ui_transform.right_of != SceneEntityId::ROOT
&& !valid_nodes.contains_key(&ui_transform.right_of)
{
blocked_elements
.entry(ui_transform.right_of)
.or_default()
.push((
scene_id,
(bevy_entity, ui_transform, transform_is_changed, root_node),
));
continue;
let skip = creation_frames
.get(&ui_transform.right_of)
.is_some_and(|&right_of_frame| right_of_frame > creation_frame);
if !skip {
blocked_elements
.entry(ui_transform.right_of)
.or_default()
.push((
scene_id,
(
bevy_entity,
ui_transform,
transform_is_changed,
root_node,
creation_frame,
),
));
continue;
}
}

// if our parent is not added, we can't process this node
Expand All @@ -879,7 +922,13 @@ fn layout_scene_ui(
.or_default()
.push((
scene_id,
(bevy_entity, ui_transform, transform_is_changed, root_node),
(
bevy_entity,
ui_transform,
transform_is_changed,
root_node,
creation_frame,
),
));
continue;
};
Expand Down Expand Up @@ -1033,7 +1082,9 @@ fn layout_scene_ui(
interactors,
};

commands.entity(bevy_entity).try_insert(new_link.clone());
commands
.entity(bevy_entity)
.try_insert((new_link.clone(), UiCreationOrder(creation_frame)));
valid_nodes.insert(scene_id, new_link);
false
};
Expand Down
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