agg_gui/widgets/
collapsing_header.rs

1//! `CollapsingHeader` — a clickable header that shows/hides child content.
2//!
3//! # Composition
4//!
5//! ```text
6//! CollapsingHeader
7//!   ├── Label (header text, drawn manually)
8//!   └── child widget (shown when expanded, hidden when collapsed)
9//! ```
10//!
11//! The triangle indicator is drawn as a path.  Clicking anywhere on the header
12//! row toggles the collapsed/expanded state.
13
14use std::sync::Arc;
15
16use crate::color::Color;
17use crate::draw_ctx::DrawCtx;
18use crate::event::{Event, EventResult, MouseButton};
19use crate::geometry::{Point, Rect, Size};
20use crate::text::Font;
21use crate::widget::{Widget, paint_subtree};
22use crate::widgets::label::Label;
23
24const HEADER_H: f64 = 22.0;
25const TRIANGLE_SIZE: f64 = 6.0;
26const INDENT: f64 = 12.0;
27
28/// A collapsible section header.  When expanded, the child widget is visible
29/// below the header row.  When collapsed, only the header row is shown.
30pub struct CollapsingHeader {
31    bounds:    Rect,
32    children:  Vec<Box<dyn Widget>>,
33    label:     Label,
34    open:      bool,
35    hovered:   bool,
36    /// The content shown when expanded.
37    content:   Option<Box<dyn Widget>>,
38}
39
40impl CollapsingHeader {
41    /// Create a new header with the given text, using the provided font.
42    /// Starts expanded by default.
43    pub fn new(text: impl Into<String>, font: Arc<Font>) -> Self {
44        let label = Label::new(text, Arc::clone(&font)).with_font_size(13.0);
45        Self {
46            bounds:   Rect::default(),
47            children: Vec::new(),
48            label,
49            open:     true,
50            hovered:  false,
51            content:  None,
52        }
53    }
54
55    /// Set whether the section is open (expanded) by default.
56    pub fn default_open(mut self, open: bool) -> Self {
57        self.open = open;
58        self
59    }
60
61    /// Set the child content widget shown when expanded.
62    pub fn with_content(mut self, content: Box<dyn Widget>) -> Self {
63        self.content = Some(content);
64        self
65    }
66}
67
68impl Widget for CollapsingHeader {
69    fn type_name(&self) -> &'static str { "CollapsingHeader" }
70    fn bounds(&self) -> Rect { self.bounds }
71    fn set_bounds(&mut self, b: Rect) { self.bounds = b; }
72    fn children(&self) -> &[Box<dyn Widget>] { &self.children }
73    fn children_mut(&mut self) -> &mut Vec<Box<dyn Widget>> { &mut self.children }
74
75    fn layout(&mut self, available: Size) -> Size {
76        let w = available.width;
77
78        // Sync `children` with `open` state so the framework dispatches events
79        // to the content only when it is visible.  When closed the content
80        // lives in `self.content`; when open it lives in `self.children[0]`.
81        if self.open && self.children.is_empty() {
82            if let Some(c) = self.content.take() {
83                self.children.push(c);
84            }
85        } else if !self.open && !self.children.is_empty() {
86            if let Some(c) = self.children.pop() {
87                self.content = Some(c);
88            }
89        }
90
91        // Layout label inside the header row.
92        let label_available = Size::new(w - INDENT - TRIANGLE_SIZE * 2.0, HEADER_H);
93        let ls = self.label.layout(label_available);
94        let ly = (HEADER_H - ls.height) * 0.5;
95        self.label.set_bounds(Rect::new(INDENT + TRIANGLE_SIZE * 2.0 + 4.0, ly, ls.width, ls.height));
96
97        // Layout content if open — as a child so the framework paints and
98        // dispatches events normally.  Content is inset from the left by
99        // INDENT * 0.5 for visual hierarchy.
100        let content_h = if self.open && !self.children.is_empty() {
101            let inset = INDENT * 0.5;
102            let avail_w = (w - inset).max(0.0);
103            let child = &mut self.children[0];
104            let cs = child.layout(Size::new(avail_w, available.height - HEADER_H));
105            // Content sits at the bottom of our bounds (Y-up: y = 0).
106            child.set_bounds(Rect::new(inset, 0.0, cs.width, cs.height));
107            cs.height
108        } else {
109            0.0
110        };
111
112        let total_h = HEADER_H + content_h;
113        self.bounds = Rect::new(0.0, 0.0, w, total_h);
114        Size::new(w, total_h)
115    }
116
117    fn paint(&mut self, ctx: &mut dyn DrawCtx) {
118        let v = ctx.visuals();
119        let w = self.bounds.width;
120        let h = self.bounds.height;
121
122        // Header row background — always shown at a subtle tint so the header
123        // reads as a distinct section boundary even when not hovered.  Hover
124        // deepens the tint slightly as click affordance.  Sits just below the
125        // top divider line so the line remains crisp.
126        let alpha = if self.hovered { 0.10 } else { 0.06 };
127        ctx.set_fill_color(Color::rgba(
128            v.text_color.r, v.text_color.g, v.text_color.b, alpha,
129        ));
130        ctx.begin_path();
131        ctx.rect(0.0, h - HEADER_H, w, HEADER_H - 1.0);
132        ctx.fill();
133
134        // Top divider line — 1px, full-width, in the shared separator colour
135        // so a vertical stack of headers forms consistent section boundaries
136        // matching any `Separator` widgets elsewhere in the UI.
137        ctx.set_fill_color(v.separator);
138        ctx.begin_path();
139        ctx.rect(0.0, h - 1.0, w, 1.0);
140        ctx.fill();
141
142        // Triangle indicator (▶ collapsed, ▼ expanded).
143        // In Y-up: the header row occupies y = h - HEADER_H .. h.
144        let center_y = h - HEADER_H * 0.5;
145        let tx = INDENT;
146        let ts = TRIANGLE_SIZE * 0.5;
147        ctx.set_fill_color(v.text_dim);
148        ctx.begin_path();
149        if self.open {
150            // Pointing down (▼): triangle with point at bottom.
151            ctx.move_to(tx,          center_y + ts * 0.5);
152            ctx.line_to(tx + ts * 2.0, center_y + ts * 0.5);
153            ctx.line_to(tx + ts,       center_y - ts * 0.8);
154        } else {
155            // Pointing right (▶): triangle with point to the right.
156            ctx.move_to(tx,            center_y + ts);
157            ctx.line_to(tx,            center_y - ts);
158            ctx.line_to(tx + ts * 1.6, center_y);
159        }
160        ctx.fill();
161
162        // Label.
163        self.label.set_color(v.text_color);
164        let lb = self.label.bounds();
165        // Label y is in header-local coords, but header is at top of our bounds (in Y-up).
166        let label_offset_y = h - HEADER_H + lb.y;
167        ctx.save();
168        ctx.translate(lb.x, label_offset_y);
169        paint_subtree(&mut self.label, ctx);
170        ctx.restore();
171
172        // Content is painted by the framework via normal child recursion —
173        // it lives in `self.children[0]` (when open) and has its own bounds
174        // so `dispatch_event` reaches it without manual forwarding.
175    }
176
177    fn on_event(&mut self, event: &Event) -> EventResult {
178        let h = self.bounds.height;
179
180        match event {
181            Event::MouseMove { pos } => {
182                // Header row: top portion in Y-up = y from (h - HEADER_H) to h.
183                let in_header = pos.x >= 0.0 && pos.x <= self.bounds.width
184                    && pos.y >= h - HEADER_H && pos.y <= h;
185                let was = self.hovered;
186                self.hovered = in_header;
187                if self.hovered != was {
188                    crate::animation::request_tick();
189                    return EventResult::Consumed;
190                }
191                EventResult::Ignored
192            }
193            Event::MouseDown { button: MouseButton::Left, pos, .. } => {
194                let in_header = pos.x >= 0.0 && pos.x <= self.bounds.width
195                    && pos.y >= h - HEADER_H && pos.y <= h;
196                if in_header {
197                    self.open = !self.open;
198                    crate::animation::request_tick();
199                    return EventResult::Consumed;
200                }
201                EventResult::Ignored
202            }
203            _ => EventResult::Ignored,
204        }
205    }
206
207    fn hit_test(&self, local_pos: Point) -> bool {
208        local_pos.x >= 0.0 && local_pos.x <= self.bounds.width
209            && local_pos.y >= 0.0 && local_pos.y <= self.bounds.height
210    }
211}
agg_gui/widgets/collapsing_header.rs

agg_gui/widgets/
collapsing_header.rs
