cranpose_app_shell/

focus_reveal.rs

use cranpose_core::{NodeId, run_in_mutable_snapshot};
use cranpose_foundation::{ScrollAxisRange, SemanticsScrollBy};
use cranpose_render_common::Renderer;
use cranpose_ui::{LayoutBox, SemanticsNode, layout::can_skip_scroll_reveal_from_applier};
use cranpose_ui_graphics::Rect;

use crate::AppShell;

impl<R: Renderer> AppShell<R>
where
    R::Error: std::fmt::Debug,
{
    /// Reveals a screen reader's target without changing keyboard focus.
    ///
    /// Hidden, disabled, removed and modal-background targets are rejected.
    /// Returns whether a scroll action reports movement.
    pub fn accessibility_reveal(&mut self, node_id: NodeId) -> bool {
        let _app_context = self.app.app_context.enter_scope();
        self.reveal_node_in_context(node_id)
    }

    pub(crate) fn reveal_new_focus(&mut self) {
        let focused = self.app.app_context.active_focus_target();
        if focused == self.app.revealed_focus {
            return;
        }
        self.app.revealed_focus = focused;
        let Some(focused) = focused else { return };
        self.reveal_node_with(focused, true);
    }

    fn reveal_node_in_context(&mut self, focused: NodeId) -> bool {
        self.reveal_node_with(focused, false)
    }

    /// Out of line: a frame checks for a newly focused node and seldom finds
    /// one, so the frame's own code stays small.
    #[inline(never)]
    fn reveal_node_with(&mut self, focused: NodeId, remeasure_containers: bool) -> bool {
        let mut revealed = false;
        for index in 0..self.surfaces.len() {
            let surface = &self.surfaces[index];
            if surface.layout_tree.is_none() && surface.semantics_tree.is_none() {
                self.app.flush_semantics_invalidations();
                if let Some(root) = surface.root_node(&self.app)
                    && can_skip_scroll_reveal_from_applier(
                        &mut self.app.composition.applier_mut(),
                        root,
                        focused,
                    )
                    .unwrap_or(false)
                {
                    continue;
                }
            }
            let ancestors = self.surfaces[index]
                .semantics_tree_for_input(&mut self.app)
                .and_then(|tree| scroll_ancestors(tree.root(), focused))
                .unwrap_or_default();
            if remeasure_containers && !ancestors.is_empty() {
                for &ancestor in &ancestors {
                    cranpose_ui::schedule_measure_repass(ancestor);
                }
                self.app.request_layout_pass();
                self.run_layout_phase_in_context();
            }
            for ancestor in ancestors {
                revealed |= self.reveal_within_container(index, focused, ancestor);
            }
        }
        revealed
    }

    fn reveal_within_container(&mut self, index: usize, focused: NodeId, ancestor: NodeId) -> bool {
        let mut revealed = false;
        let mut previous_distance = f32::INFINITY;
        loop {
            let surface = &mut self.surfaces[index];
            let request = surface
                .layout_tree_in_context(&mut self.app)
                .and_then(|tree| {
                    Some((
                        bounds_of(tree.root(), focused)?,
                        bounds_of(tree.root(), ancestor)?,
                    ))
                })
                .and_then(|(target, viewport)| {
                    let tree = surface.semantics_tree_for_input(&mut self.app)?;
                    scroll_request(semantics_of(tree.root(), ancestor)?, target, viewport)
                });
            let Some((action, dx, dy)) = request else {
                break;
            };
            let distance = dx.abs() + dy.abs();
            if distance >= previous_distance {
                break;
            }
            previous_distance = distance;
            if !run_in_mutable_snapshot(|| action.invoke(dx, dy)).unwrap_or(false) {
                break;
            }
            revealed = true;
            self.app.request_layout_pass();
            self.run_layout_phase_in_context();
        }
        revealed
    }
}

pub(crate) fn scroll_ancestors(node: &SemanticsNode, target: NodeId) -> Option<Vec<NodeId>> {
    if node.hidden || !node.enabled {
        return None;
    }
    if node.node_id == target {
        return Some(Vec::new());
    }
    let mut path = node
        .children
        .iter()
        .find_map(|node| scroll_ancestors(node, target))?;
    if node.details().scroll_by.is_some() {
        path.push(node.node_id);
    }
    Some(path)
}

pub(crate) fn semantics_of(node: &SemanticsNode, target: NodeId) -> Option<&SemanticsNode> {
    if node.node_id == target {
        return Some(node);
    }
    node.children
        .iter()
        .find_map(|node| semantics_of(node, target))
}

pub(crate) fn bounds_of(node: &LayoutBox, target: NodeId) -> Option<Rect> {
    if node.node_id == target {
        return Some(node.rect);
    }
    node.children
        .iter()
        .find_map(|node| bounds_of(node, target))
}

fn scroll_request(
    node: &SemanticsNode,
    target: Rect,
    viewport: Rect,
) -> Option<(SemanticsScrollBy, f32, f32)> {
    let details = node.details();
    let action = details.scroll_by.clone()?;
    let dx = axis_delta(
        target.x,
        target.width,
        viewport.x,
        viewport.width,
        details.horizontal_scroll,
    );
    let dy = axis_delta(
        target.y,
        target.height,
        viewport.y,
        viewport.height,
        details.vertical_scroll,
    );
    (dx != 0.0 || dy != 0.0).then_some((action, dx, dy))
}

fn axis_delta(
    start: f32,
    size: f32,
    viewport_start: f32,
    viewport_size: f32,
    range: Option<ScrollAxisRange>,
) -> f32 {
    let Some(range) = range else { return 0.0 };
    if ![start, size, viewport_start, viewport_size]
        .iter()
        .all(|value| value.is_finite())
        || size <= 0.0
        || viewport_size <= 0.0
    {
        return 0.0;
    }
    let inset_start = range.content_padding_start.max(0.0);
    let inset_end = range.content_padding_end.max(0.0);
    let (viewport_start, viewport_size) = if viewport_size - inset_start - inset_end >= size {
        (
            viewport_start + inset_start,
            viewport_size - inset_start - inset_end,
        )
    } else {
        (viewport_start, viewport_size)
    };
    let delta = range.bring_into_view_spec.calculate_scroll_distance(
        start - viewport_start,
        size,
        viewport_size,
    );
    let delta = if range.reverse { -delta } else { delta };
    if (delta > 0.0 && range.can_scroll_forward()) || (delta < 0.0 && range.can_scroll_backward()) {
        delta
    } else {
        0.0
    }
}

#[cfg(test)]
#[path = "tests/focus_reveal_tests.rs"]
mod tests;