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use crate::{
environment::LayoutEnvironment,
event::{Event, EventResult},
focus::{DefaultFocus, FocusAction, FocusDirection},
layout::{Alignment, ResolvedLayout},
primitives::{Point, ProposedDimension, ProposedDimensions},
view::{ViewLayout, ViewMarker},
};
/// A view that uses the layout of the foreground view, but renders the background
/// behind it.
#[derive(Debug, Clone)]
pub struct BackgroundView<T, U> {
foreground: T,
background: U,
alignment: Alignment,
}
impl<T: ViewMarker, U: ViewMarker> BackgroundView<T, U> {
pub const fn new(foreground: T, background: U, alignment: Alignment) -> Self {
Self {
foreground,
background,
alignment,
}
}
}
/// Focus tree for background view - tracks which child has focus
#[derive(Debug, Clone)]
pub enum BackgroundFocus<T, U> {
/// Focus is on the foreground
Foreground(T),
/// Focus is on the background
Background(U),
}
impl<T: DefaultFocus, U: DefaultFocus> DefaultFocus for BackgroundFocus<T, U> {
fn default_first() -> Self {
Self::Background(U::default_first())
}
fn default_last() -> Self {
Self::Foreground(T::default_last())
}
}
impl<T, U> ViewMarker for BackgroundView<T, U>
where
T: ViewMarker,
U: ViewMarker,
{
type Renderables = (U::Renderables, T::Renderables);
type Transition = T::Transition;
}
impl<Captures: ?Sized, T, U> ViewLayout<Captures> for BackgroundView<T, U>
where
T: ViewLayout<Captures>,
U: ViewLayout<Captures>,
{
type Sublayout = ResolvedLayout<T::Sublayout>;
// Tuples are rendered first to last
type State = (T::State, U::State);
type FocusTree = BackgroundFocus<T::FocusTree, U::FocusTree>;
fn priority(&self) -> i8 {
self.foreground.priority()
}
fn is_empty(&self) -> bool {
self.foreground.is_empty()
}
fn transition(&self) -> Self::Transition {
self.foreground.transition()
}
fn build_state(&self, captures: &mut Captures) -> Self::State {
(
self.foreground.build_state(captures),
self.background.build_state(captures),
)
}
fn layout(
&self,
offer: &ProposedDimensions,
env: &impl LayoutEnvironment,
captures: &mut Captures,
state: &mut Self::State,
) -> ResolvedLayout<Self::Sublayout> {
self.foreground
.layout(offer, env, captures, &mut state.0)
.nested()
}
fn render_tree(
&self,
layout: &Self::Sublayout,
origin: Point,
env: &impl LayoutEnvironment,
captures: &mut Captures,
state: &mut Self::State,
) -> Self::Renderables {
let foreground_size = layout.resolved_size;
// Propose the foreground size to the background
let background_offer = ProposedDimensions {
width: ProposedDimension::Exact(foreground_size.width.into()),
height: ProposedDimension::Exact(foreground_size.height.into()),
};
let background_layout =
self.background
.layout(&background_offer, env, captures, &mut state.1);
let new_origin = origin
+ Point::new(
self.alignment.horizontal().align(
layout.resolved_size.width.into(),
background_layout.resolved_size.width.into(),
),
self.alignment.vertical().align(
layout.resolved_size.height.into(),
background_layout.resolved_size.height.into(),
),
);
(
self.background.render_tree(
&background_layout.sublayouts,
new_origin,
env,
captures,
&mut state.1,
),
self.foreground
.render_tree(&layout.sublayouts, origin, env, captures, &mut state.0),
)
}
#[expect(clippy::too_many_lines)]
fn handle_event(
&self,
event: &crate::view::Event,
context: &crate::event::EventContext,
render_tree: &mut Self::Renderables,
captures: &mut Captures,
state: &mut Self::State,
focus: &mut Self::FocusTree,
) -> EventResult {
// Handle focus events specially - they need to route through the focus tree
if let Event::Focus {
action: focus_event,
group,
} = event
{
match focus {
BackgroundFocus::Background(background_focus) => {
let result = self.background.handle_event(
event,
context,
&mut render_tree.0,
captures,
&mut state.1,
background_focus,
);
if result.is_handled() || *focus_event == FocusAction::Teardown {
return result;
}
// Background exhausted - only move to foreground on forward navigation
match focus_event {
FocusAction::Focus(FocusDirection::Forward) | FocusAction::Next => {
// Move to foreground
let mut foreground_focus = DefaultFocus::default_first();
let result = self.foreground.handle_event(
&Event::Focus {
action: FocusAction::Focus(FocusDirection::Forward),
group: *group,
},
context,
&mut render_tree.1,
captures,
&mut state.0,
&mut foreground_focus,
);
*focus = BackgroundFocus::Foreground(foreground_focus);
result
}
FocusAction::Focus(FocusDirection::Backward)
| FocusAction::Previous
| FocusAction::Blur
| FocusAction::Select
| FocusAction::Teardown => EventResult::Deferred,
}
}
BackgroundFocus::Foreground(foreground_focus) => {
let result = self.foreground.handle_event(
event,
context,
&mut render_tree.1,
captures,
&mut state.0,
foreground_focus,
);
if result.is_handled() || *focus_event == FocusAction::Teardown {
return result;
}
// Foreground exhausted - only move to background on backward navigation
match focus_event {
FocusAction::Focus(FocusDirection::Backward) | FocusAction::Previous => {
let mut background_focus = DefaultFocus::default_last();
let result = self.background.handle_event(
&Event::Focus {
action: FocusAction::Focus(FocusDirection::Backward),
group: *group,
},
context,
&mut render_tree.0,
captures,
&mut state.1,
&mut background_focus,
);
*focus = BackgroundFocus::Background(background_focus);
result
}
FocusAction::Focus(FocusDirection::Forward)
| FocusAction::Next
| FocusAction::Select
| FocusAction::Blur
| FocusAction::Teardown => EventResult::Deferred,
}
}
}
} else {
// For non-focus events (touch, scroll, etc.), perform DFS back to front
match focus {
BackgroundFocus::Background(_) => {
// Start with background (back)
let background_result = self.background.handle_event(
event,
context,
&mut render_tree.0,
captures,
&mut state.1,
match focus {
BackgroundFocus::Background(focus) => focus,
BackgroundFocus::Foreground(_) => unreachable!(),
},
);
if background_result.is_handled() {
return background_result;
}
// Then foreground (front)
*focus = BackgroundFocus::Foreground(DefaultFocus::default_first());
self.foreground.handle_event(
event,
context,
&mut render_tree.1,
captures,
&mut state.0,
match focus {
BackgroundFocus::Foreground(focus) => focus,
BackgroundFocus::Background(_) => unreachable!(),
},
)
}
BackgroundFocus::Foreground(_) => {
// Start with background (back)
*focus = BackgroundFocus::Background(DefaultFocus::default_first());
let background_result = self.background.handle_event(
event,
context,
&mut render_tree.0,
captures,
&mut state.1,
match focus {
BackgroundFocus::Background(focus) => focus,
BackgroundFocus::Foreground(_) => unreachable!(),
},
);
if background_result.is_handled() {
return background_result;
}
// Then foreground (front)
*focus = BackgroundFocus::Foreground(DefaultFocus::default_first());
self.foreground.handle_event(
event,
context,
&mut render_tree.1,
captures,
&mut state.0,
match focus {
BackgroundFocus::Foreground(focus) => focus,
BackgroundFocus::Background(_) => unreachable!(),
},
)
}
}
}
}
}