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//! `CollapsingHeader` — a clickable header that shows/hides child content.
//!
//! # Composition
//!
//! ```text
//! CollapsingHeader
//! ├── Label (header text, drawn manually)
//! └── child widget (shown when expanded, hidden when collapsed)
//! ```
//!
//! The triangle indicator is drawn as a path. Clicking anywhere on the header
//! row toggles the collapsed/expanded state.
use std::sync::Arc;
use crate::color::Color;
use crate::draw_ctx::DrawCtx;
use crate::event::{Event, EventResult, MouseButton};
use crate::geometry::{Point, Rect, Size};
use crate::text::Font;
use crate::widget::{Widget, paint_subtree};
use crate::widgets::label::Label;
const HEADER_H: f64 = 22.0;
const TRIANGLE_SIZE: f64 = 6.0;
const INDENT: f64 = 12.0;
/// A collapsible section header. When expanded, the child widget is visible
/// below the header row. When collapsed, only the header row is shown.
pub struct CollapsingHeader {
bounds: Rect,
children: Vec<Box<dyn Widget>>,
label: Label,
open: bool,
hovered: bool,
/// The content shown when expanded.
content: Option<Box<dyn Widget>>,
}
impl CollapsingHeader {
/// Create a new header with the given text, using the provided font.
/// Starts expanded by default.
pub fn new(text: impl Into<String>, font: Arc<Font>) -> Self {
let label = Label::new(text, Arc::clone(&font)).with_font_size(13.0);
Self {
bounds: Rect::default(),
children: Vec::new(),
label,
open: true,
hovered: false,
content: None,
}
}
/// Set whether the section is open (expanded) by default.
pub fn default_open(mut self, open: bool) -> Self {
self.open = open;
self
}
/// Set the child content widget shown when expanded.
pub fn with_content(mut self, content: Box<dyn Widget>) -> Self {
self.content = Some(content);
self
}
}
impl Widget for CollapsingHeader {
fn type_name(&self) -> &'static str { "CollapsingHeader" }
fn bounds(&self) -> Rect { self.bounds }
fn set_bounds(&mut self, b: Rect) { self.bounds = b; }
fn children(&self) -> &[Box<dyn Widget>] { &self.children }
fn children_mut(&mut self) -> &mut Vec<Box<dyn Widget>> { &mut self.children }
fn layout(&mut self, available: Size) -> Size {
let w = available.width;
// Sync `children` with `open` state so the framework dispatches events
// to the content only when it is visible. When closed the content
// lives in `self.content`; when open it lives in `self.children[0]`.
if self.open && self.children.is_empty() {
if let Some(c) = self.content.take() {
self.children.push(c);
}
} else if !self.open && !self.children.is_empty() {
if let Some(c) = self.children.pop() {
self.content = Some(c);
}
}
// Layout label inside the header row.
let label_available = Size::new(w - INDENT - TRIANGLE_SIZE * 2.0, HEADER_H);
let ls = self.label.layout(label_available);
let ly = (HEADER_H - ls.height) * 0.5;
self.label.set_bounds(Rect::new(INDENT + TRIANGLE_SIZE * 2.0 + 4.0, ly, ls.width, ls.height));
// Layout content if open — as a child so the framework paints and
// dispatches events normally. Content is inset from the left by
// INDENT * 0.5 for visual hierarchy.
let content_h = if self.open && !self.children.is_empty() {
let inset = INDENT * 0.5;
let avail_w = (w - inset).max(0.0);
let child = &mut self.children[0];
let cs = child.layout(Size::new(avail_w, available.height - HEADER_H));
// Content sits at the bottom of our bounds (Y-up: y = 0).
child.set_bounds(Rect::new(inset, 0.0, cs.width, cs.height));
cs.height
} else {
0.0
};
let total_h = HEADER_H + content_h;
self.bounds = Rect::new(0.0, 0.0, w, total_h);
Size::new(w, total_h)
}
fn paint(&mut self, ctx: &mut dyn DrawCtx) {
let v = ctx.visuals();
let w = self.bounds.width;
let h = self.bounds.height;
// Header row background — always shown at a subtle tint so the header
// reads as a distinct section boundary even when not hovered. Hover
// deepens the tint slightly as click affordance. Sits just below the
// top divider line so the line remains crisp.
let alpha = if self.hovered { 0.10 } else { 0.06 };
ctx.set_fill_color(Color::rgba(
v.text_color.r, v.text_color.g, v.text_color.b, alpha,
));
ctx.begin_path();
ctx.rect(0.0, h - HEADER_H, w, HEADER_H - 1.0);
ctx.fill();
// Top divider line — 1px, full-width, in the shared separator colour
// so a vertical stack of headers forms consistent section boundaries
// matching any `Separator` widgets elsewhere in the UI.
ctx.set_fill_color(v.separator);
ctx.begin_path();
ctx.rect(0.0, h - 1.0, w, 1.0);
ctx.fill();
// Triangle indicator (▶ collapsed, ▼ expanded).
// In Y-up: the header row occupies y = h - HEADER_H .. h.
let center_y = h - HEADER_H * 0.5;
let tx = INDENT;
let ts = TRIANGLE_SIZE * 0.5;
ctx.set_fill_color(v.text_dim);
ctx.begin_path();
if self.open {
// Pointing down (▼): triangle with point at bottom.
ctx.move_to(tx, center_y + ts * 0.5);
ctx.line_to(tx + ts * 2.0, center_y + ts * 0.5);
ctx.line_to(tx + ts, center_y - ts * 0.8);
} else {
// Pointing right (▶): triangle with point to the right.
ctx.move_to(tx, center_y + ts);
ctx.line_to(tx, center_y - ts);
ctx.line_to(tx + ts * 1.6, center_y);
}
ctx.fill();
// Label.
self.label.set_color(v.text_color);
let lb = self.label.bounds();
// Label y is in header-local coords, but header is at top of our bounds (in Y-up).
let label_offset_y = h - HEADER_H + lb.y;
ctx.save();
ctx.translate(lb.x, label_offset_y);
paint_subtree(&mut self.label, ctx);
ctx.restore();
// Content is painted by the framework via normal child recursion —
// it lives in `self.children[0]` (when open) and has its own bounds
// so `dispatch_event` reaches it without manual forwarding.
}
fn on_event(&mut self, event: &Event) -> EventResult {
let h = self.bounds.height;
match event {
Event::MouseMove { pos } => {
// Header row: top portion in Y-up = y from (h - HEADER_H) to h.
let in_header = pos.x >= 0.0 && pos.x <= self.bounds.width
&& pos.y >= h - HEADER_H && pos.y <= h;
let was = self.hovered;
self.hovered = in_header;
if self.hovered != was {
crate::animation::request_tick();
return EventResult::Consumed;
}
EventResult::Ignored
}
Event::MouseDown { button: MouseButton::Left, pos, .. } => {
let in_header = pos.x >= 0.0 && pos.x <= self.bounds.width
&& pos.y >= h - HEADER_H && pos.y <= h;
if in_header {
self.open = !self.open;
crate::animation::request_tick();
return EventResult::Consumed;
}
EventResult::Ignored
}
_ => EventResult::Ignored,
}
}
fn hit_test(&self, local_pos: Point) -> bool {
local_pos.x >= 0.0 && local_pos.x <= self.bounds.width
&& local_pos.y >= 0.0 && local_pos.y <= self.bounds.height
}
}