cranpose_liquid/widgets/
nav_bar.rs

1use std::{cell::RefCell, rc::Rc};
2
3use cranpose_macros::composable;
4use cranpose_ui::{
5    Dp, Modifier, ScrollState,
6    text::{SpanStyle, TextStyle},
7    widgets::{Box, BoxSpec, Row, RowSpec, Text},
8};
9use cranpose_ui_graphics::{Brush, GradientBlurDirection, GraphicsLayer};
10use cranpose_ui_layout::{Alignment, VerticalAlignment};
11
12use crate::theme::{liquid_colors, liquid_typography};
13
14/// Configuration for [`LiquidNavBar`].
15#[derive(Clone, Debug, PartialEq)]
16pub struct LiquidNavBarSpec {
17    pub title: String,
18    /// Scroll distance (dp) over which the large title collapses.
19    pub collapse_range: f32,
20}
21
22impl LiquidNavBarSpec {
23    pub fn new(title: impl Into<String>) -> Self {
24        Self {
25            title: title.into(),
26            collapse_range: 52.0,
27        }
28    }
29}
30
31const BAR_HEIGHT: f32 = 52.0;
32const LARGE_TITLE_HEIGHT: f32 = 52.0;
33const BAND_BLUR_TOP_DP: f32 = 18.0;
34const BAND_BLUR_BOTTOM_DP: f32 = 0.35;
35const SCRIM_TOP_ALPHA: f32 = 0.82;
36const SCRIM_MIDDLE_ALPHA: f32 = 0.40;
37
38/// A large-title navigation bar driven by the content's [`ScrollState`]
39/// (offset 0 = top). `leading`/`trailing` compose the bar buttons.
40///
41/// The bar installs a settle policy on the scroll so it can never rest inside
42/// the large-title collapse band — releasing (or wheel-idling) mid-band snaps
43/// to fully expanded or fully collapsed, exactly like `UINavigationBar`. The
44/// large title composes UNDER the band, so mid-collapse it slides beneath
45/// the blur instead of floating readable next to the inline title.
46///
47/// The band is the crown the showcase and cranscan headers wear: a gradient
48/// blur, frosted at the top edge and sharp where the content emerges, under
49/// a scrim of the background colour, both fading in with the collapse.
50///
51/// Place the bar *after* the scrolling content inside a `Box` so its blur
52/// reads the content sliding underneath.
53#[composable]
54pub fn LiquidNavBar(
55    modifier: Modifier,
56    spec: LiquidNavBarSpec,
57    scroll: ScrollState,
58    leading: impl FnMut() + 'static,
59    trailing: impl FnMut() + 'static,
60) {
61    let colors = liquid_colors();
62    let typography = liquid_typography();
63    let leading = Rc::new(RefCell::new(leading));
64    let trailing = Rc::new(RefCell::new(trailing));
65
66    let collapse_range = spec.collapse_range;
67    if std::env::var_os("CRANPOSE_DISABLE_NAV_SNAP").is_none() {
68        scroll.set_settle_policy(Some(large_title_settle_policy(collapse_range)));
69    }
70    let scroll_offset = scroll.value();
71
72    let progress = (scroll_offset / spec.collapse_range.max(1.0)).clamp(0.0, 1.0);
73    let title = spec.title;
74
75    Box(modifier, BoxSpec::default(), move || {
76        let large_alpha = (1.0 - progress * 1.6).clamp(0.0, 1.0);
77        if large_alpha > 0.0 {
78            let style = TextStyle {
79                span_style: SpanStyle {
80                    color: Some(colors.label.with_alpha(large_alpha)),
81                    ..typography.large_title.span_style.clone()
82                },
83                ..typography.large_title.clone()
84            };
85            let slide = -scroll_offset.min(collapse_range);
86            let large_title = title.clone();
87            Box(
88                Modifier::empty()
89                    .offset(16.0, BAR_HEIGHT)
90                    .height(LARGE_TITLE_HEIGHT)
91                    .graphics_layer(move || GraphicsLayer {
92                        translation_y: slide,
93                        ..Default::default()
94                    }),
95                BoxSpec::default().content_alignment(Alignment::new(
96                    cranpose_ui_layout::HorizontalAlignment::Start,
97                    cranpose_ui_layout::VerticalAlignment::CenterVertically,
98                )),
99                move || {
100                    Text(large_title.clone(), Modifier::empty(), style.clone());
101                },
102            );
103        }
104
105        let background = colors.background;
106        let band = Modifier::empty()
107            .fill_max_width()
108            .height(BAR_HEIGHT)
109            .backdrop_gradient_blur(
110                Dp(BAND_BLUR_TOP_DP * progress),
111                Dp(BAND_BLUR_BOTTOM_DP * progress),
112                GradientBlurDirection::TopToBottom,
113            )
114            .draw_behind(move |scope| {
115                scope.draw_rect(Brush::vertical_gradient(
116                    vec![
117                        background.with_alpha(SCRIM_TOP_ALPHA * progress),
118                        background.with_alpha(SCRIM_MIDDLE_ALPHA * progress),
119                        background.with_alpha(0.0),
120                    ],
121                    0.0,
122                    scope.size().height,
123                ));
124            });
125        Box(band, BoxSpec::default(), || {});
126
127        let inline_alpha = ((progress - 0.5) * 2.0).clamp(0.0, 1.0);
128        let inline_title = title.clone();
129        let inline_typography = typography.clone();
130        let leading = Rc::clone(&leading);
131        let trailing = Rc::clone(&trailing);
132        Row(
133            Modifier::empty()
134                .fill_max_width()
135                .height(BAR_HEIGHT)
136                .padding_horizontal(10.0),
137            RowSpec::default().vertical_alignment(VerticalAlignment::CenterVertically),
138            move || {
139                (leading.borrow_mut())();
140                let style = TextStyle {
141                    span_style: SpanStyle {
142                        color: Some(colors.label.with_alpha(inline_alpha)),
143                        ..inline_typography.headline.span_style.clone()
144                    },
145                    ..inline_typography.headline.clone()
146                };
147                let inline_title = inline_title.clone();
148                Box(
149                    Modifier::empty().weight(1.0),
150                    BoxSpec::default().content_alignment(Alignment::CENTER),
151                    move || {
152                        Text(inline_title.clone(), Modifier::empty(), style.clone());
153                    },
154                );
155                (trailing.borrow_mut())();
156            },
157        );
158    });
159}
160
161pub fn large_title_settle_policy(collapse_range: f32) -> cranpose_ui::ScrollSettlePolicy {
162    let range = collapse_range.max(1.0);
163    Rc::new(move |proposed: f32, _velocity: f32| {
164        if proposed <= 0.0 || proposed >= range {
165            proposed
166        } else if proposed < range * 0.5 {
167            0.0
168        } else {
169            range
170        }
171    })
172}
173
174/// Total height the bar family occupies while expanded (inline bar + large
175/// title) — content's top padding.
176pub fn liquid_nav_bar_expanded_height() -> f32 {
177    BAR_HEIGHT + LARGE_TITLE_HEIGHT
178}
179
180#[cfg(test)]
181#[path = "tests/nav_bar_tests.rs"]
182mod tests;
cranpose_liquid/widgets/nav_bar.rs

cranpose_liquid/widgets/
nav_bar.rs
