cranpose_services/
accessibility_state.rs

1//! What the platform says about the assistive technology in use, for an app
2//! that speaks guidance, slows an automatic step down or drops a gesture-only
3//! path while a screen reader is on.
4
5use std::cell::{Cell, RefCell};
6
7use cranpose_core::{CompositionLocal, CompositionLocalProvider, compositionLocalOf};
8use cranpose_macros::composable;
9
10/// What the platform reports about the assistive technology in use.
11#[derive(Clone, Copy, Debug, PartialEq, Eq, Default)]
12pub struct AccessibilityState {
13    /// Whether a screen reader is on: VoiceOver on iOS, a service such as
14    /// TalkBack on Android, or a reader that connected to the app through
15    /// accesskit on the desktop. The web has no such signal and says no.
16    pub screen_reader_on: bool,
17}
18
19thread_local! {
20    static PLATFORM_ACCESSIBILITY_STATE: Cell<AccessibilityState> =
21        const { Cell::new(AccessibilityState { screen_reader_on: false }) };
22}
23
24/// Installs what the platform reports. A backend calls this on every check
25/// and forces a root render when the answer is true, so composition reads
26/// the new state.
27pub fn set_platform_accessibility_state(state: AccessibilityState) -> bool {
28    PLATFORM_ACCESSIBILITY_STATE.with(|cell| {
29        let changed = cell.get() != state;
30        cell.set(state);
31        changed
32    })
33}
34
35/// What the platform last reported.
36pub fn platform_accessibility_state() -> AccessibilityState {
37    PLATFORM_ACCESSIBILITY_STATE.with(Cell::get)
38}
39
40/// The state a composable reads: what the platform reported, unless a
41/// [`ProvideAccessibilityState`] above it says otherwise.
42pub fn local_accessibility_state() -> CompositionLocal<AccessibilityState> {
43    thread_local! {
44        static LOCAL: RefCell<Option<CompositionLocal<AccessibilityState>>> =
45            const { RefCell::new(None) };
46    }
47
48    LOCAL.with(|cell| {
49        let mut local = cell.borrow_mut();
50        local
51            .get_or_insert_with(|| compositionLocalOf(platform_accessibility_state))
52            .clone()
53    })
54}
55
56/// Gives the content below it a fixed state, for a preview or a test that
57/// wants to see the app as a screen reader user does.
58#[composable]
59pub fn ProvideAccessibilityState(state: AccessibilityState, content: impl FnOnce()) {
60    let local = local_accessibility_state();
61    CompositionLocalProvider(vec![local.provides(state)], move || {
62        content();
63    });
64}
65
66#[cfg(test)]
67#[path = "tests/accessibility_state_tests.rs"]
68mod tests;
cranpose_services/accessibility_state.rs

cranpose_services/
accessibility_state.rs
