cranpose_ui/widgets/
layout.rs

1//! Generic Layout widget and SubcomposeLayout
2
3#![allow(non_snake_case)]
4
5use std::{cell::RefCell, rc::Rc};
6
7use cranpose_core::{NodeId, SlotId};
8use cranpose_ui_graphics::Size;
9use cranpose_ui_layout::{MeasurePolicy, Placement};
10
11use super::{nodes::LayoutNode, scopes::BoxWithConstraintsScopeImpl};
12use crate::{
13    composable,
14    modifier::Modifier,
15    subcompose_layout::{
16        Constraints, MeasurePolicy as SubcomposeMeasurePolicy, MeasureResult, SubcomposeLayoutNode,
17        SubcomposeLayoutScope, SubcomposeMeasureScope, SubcomposeMeasureScopeImpl,
18    },
19};
20
21struct RetainedMeasurePolicy<P> {
22    value: P,
23    policy: Rc<dyn MeasurePolicy>,
24}
25
26#[composable]
27pub fn Layout<F, P>(modifier: Modifier, measure_policy: P, mut content: F) -> NodeId
28where
29    F: FnMut() + 'static,
30    P: MeasurePolicy + Clone + PartialEq + 'static,
31{
32    let policy_holder = cranpose_core::remember({
33        let measure_policy = measure_policy.clone();
34        move || {
35            Rc::new(RefCell::new(RetainedMeasurePolicy {
36                value: measure_policy.clone(),
37                policy: Rc::new(measure_policy),
38            }))
39        }
40    })
41    .with(|holder| holder.clone());
42    let policy = {
43        let mut holder = policy_holder.borrow_mut();
44        if holder.value != measure_policy {
45            holder.value = measure_policy.clone();
46            holder.policy = Rc::new(measure_policy);
47        }
48        Rc::clone(&holder.policy)
49    };
50    let modifier_for_reset = modifier.clone();
51    let policy_for_reset = Rc::clone(&policy);
52    let id = cranpose_core::with_current_composer(|composer| {
53        composer.emit_recyclable_node(
54            || LayoutNode::new(modifier.clone(), Rc::clone(&policy)),
55            move |node| {
56                *node = LayoutNode::new(modifier_for_reset.clone(), Rc::clone(&policy_for_reset));
57            },
58        )
59    });
60    let composed_density = crate::density::density();
61    if let Err(err) = cranpose_core::with_node_mut(id, |node: &mut LayoutNode| {
62        node.set_modifier(modifier.clone());
63        node.set_measure_policy(Rc::clone(&policy));
64        node.set_density(composed_density);
65    }) {
66        debug_assert!(false, "failed to update Layout node: {err}");
67    }
68    cranpose_core::push_parent(id);
69    content();
70    cranpose_core::pop_parent();
71    id
72}
73
74#[composable]
75pub fn SubcomposeLayout(
76    modifier: Modifier,
77    measure_policy: impl for<'scope> Fn(
78        &mut SubcomposeMeasureScopeImpl<'scope>,
79        Constraints,
80    ) -> MeasureResult
81    + 'static,
82) -> NodeId {
83    cranpose_core::debug_label_current_scope("SubcomposeLayout");
84    let policy_cell =
85        cranpose_core::remember(|| Rc::new(RefCell::new(None::<Rc<SubcomposeMeasurePolicy>>)))
86            .with(|cell| cell.clone());
87    let current_policy: Rc<SubcomposeMeasurePolicy> = Rc::new(measure_policy);
88    let policy_captures_changed = {
89        let mut policy_cell_ref = policy_cell.borrow_mut();
90        let changed = policy_cell_ref
91            .as_ref()
92            .is_none_or(|previous| !Rc::ptr_eq(previous, &current_policy));
93        *policy_cell_ref = Some(current_policy);
94        changed
95    };
96    let policy: Rc<SubcomposeMeasurePolicy> = cranpose_core::remember(move || {
97        let policy_cell = policy_cell.clone();
98        let policy: Rc<SubcomposeMeasurePolicy> =
99            Rc::new(
100                move |scope, constraints| match policy_cell.borrow().as_ref().cloned() {
101                    Some(current) => current(scope, constraints),
102                    None => empty_subcompose_measure_result(constraints),
103                },
104            );
105        policy
106    })
107    .with(|policy| policy.clone());
108    let id = cranpose_core::with_current_composer(|composer| {
109        composer.emit_node(|| SubcomposeLayoutNode::new(modifier.clone(), Rc::clone(&policy)))
110    });
111    let captured_context =
112        cranpose_core::with_current_composer(|composer| composer.capture_composition_context());
113    let composed_density = crate::density::density();
114    if let Err(err) = cranpose_core::with_node_mut(id, |node: &mut SubcomposeLayoutNode| {
115        node.set_modifier(modifier.clone());
116        node.set_measure_policy(Rc::clone(&policy));
117        node.set_captured_context(captured_context.clone());
118        node.set_density(composed_density);
119        if policy_captures_changed {
120            node.invalidate_subcomposition();
121        }
122    }) {
123        debug_assert!(false, "failed to update SubcomposeLayout node: {err}");
124    }
125    id
126}
127
128fn empty_subcompose_measure_result(constraints: Constraints) -> MeasureResult {
129    let (width, height) = constraints.constrain(0.0, 0.0);
130    MeasureResult::new(Size { width, height }, Vec::new())
131}
132
133#[composable(no_skip)]
134pub fn BoxWithConstraints<F>(modifier: Modifier, content: F) -> NodeId
135where
136    F: FnMut(BoxWithConstraintsScopeImpl) + 'static,
137{
138    let content_ref: Rc<RefCell<F>> = Rc::new(RefCell::new(content));
139    SubcomposeLayout(modifier, move |scope, constraints| {
140        let scope_impl = BoxWithConstraintsScopeImpl::new(constraints);
141        let scope_for_content = scope_impl;
142        let measurables = {
143            let content_ref = Rc::clone(&content_ref);
144            scope.subcompose(SlotId::new(0), constraints, move || {
145                cranpose_core::debug_label_current_scope("BoxWithConstraints.slot(0)");
146                let mut content = content_ref.borrow_mut();
147                content(scope_for_content);
148            })
149        };
150        let child_constraints = Constraints {
151            min_width: 0.0,
152            max_width: constraints.max_width,
153            min_height: 0.0,
154            max_height: constraints.max_height,
155        };
156
157        let mut width = 0.0_f32;
158        let mut height = 0.0_f32;
159        let mut placements = Vec::with_capacity(measurables.len());
160
161        for measurable in measurables {
162            let placeable = scope.measure(measurable, child_constraints);
163            width = width.max(placeable.width());
164            height = height.max(placeable.height());
165            placeable.place(0.0, 0.0);
166            placements.push(Placement::new(placeable.node_id(), 0.0, 0.0, 0));
167        }
168
169        width = width.clamp(constraints.min_width, constraints.max_width);
170        height = height.clamp(constraints.min_height, constraints.max_height);
171        scope.layout(width, height, placements)
172    })
173}
174
175#[cfg(test)]
176mod tests {
177    use std::cell::Cell;
178
179    use cranpose_core::{Composition, MemoryApplier, MutableState, location_key};
180
181    use super::*;
182
183    #[test]
184    fn layout_recomposes_when_content_reads_state() {
185        let _app_context = crate::render_state::app_context_test_scope();
186        thread_local! {
187            static INVOCATIONS: Cell<usize> = const { Cell::new(0) };
188        }
189
190        let mut composition = Composition::new(MemoryApplier::new());
191        let runtime = composition.runtime_handle();
192        let state = MutableState::with_runtime(0_i32, runtime);
193
194        composition
195            .render(location_key(file!(), line!(), column!()), {
196                let observed_state = state;
197                move || {
198                    Layout(
199                        Modifier::empty(),
200                        crate::layout::policies::EmptyMeasurePolicy,
201                        {
202                            let observed_state = observed_state;
203                            move || {
204                                let _ = observed_state.value();
205                                INVOCATIONS.with(|calls| calls.set(calls.get() + 1));
206                            }
207                        },
208                    );
209                }
210            })
211            .expect("initial layout render");
212
213        INVOCATIONS.with(|calls| assert_eq!(calls.get(), 1));
214
215        state.set_value(1);
216        composition
217            .process_invalid_scopes()
218            .expect("layout content recomposition");
219
220        INVOCATIONS.with(|calls| assert_eq!(calls.get(), 2));
221    }
222
223    #[test]
224    fn subcompose_missing_policy_cell_measures_empty_layout() {
225        let result = empty_subcompose_measure_result(Constraints {
226            min_width: 12.0,
227            max_width: 120.0,
228            min_height: 8.0,
229            max_height: 90.0,
230        });
231
232        assert_eq!(result.size.width, 12.0);
233        assert_eq!(result.size.height, 8.0);
234        assert!(result.placements.is_empty());
235    }
236}
cranpose_ui/widgets/layout.rs

cranpose_ui/widgets/
layout.rs
