slint/internal/backends/winit/accesskit.rs

// Copyright © SixtyFPS GmbH <info@slint.dev>
// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-Royalty-free-1.1 OR LicenseRef-Slint-commercial

use std::cell::{Cell, RefCell};
use std::collections::HashMap;
use std::pin::Pin;
use std::ptr::NonNull;
use std::rc::Weak;
use std::sync::{Arc, Condvar, Mutex};

use accesskit::{
    Action, ActionRequest, Checked, Node, NodeBuilder, NodeId, Role, Tree, TreeUpdate,
};
use i_slint_core::accessibility::AccessibleStringProperty;
use i_slint_core::item_tree::{ItemTreeRc, ItemTreeRef, ItemTreeWeak};
use i_slint_core::items::{ItemRc, WindowItem};
use i_slint_core::lengths::ScaleFactor;
use i_slint_core::window::WindowInner;
use i_slint_core::{properties::PropertyTracker, window::WindowAdapter};

use super::WinitWindowAdapter;

/// The AccessKit adapter tries to keep the given window adapter's item tree in sync with accesskit's node tree.
///
/// The entire item tree is mapped to accesskit's node tree. Any changes to an individual accessible item results
/// in an access kit tree update with just changed nodes. Any changes in the tree structure result in a complete
/// tree rebuild. This could be implemented more efficiently, but that isn't essential; AccessKit will avoid firing
/// gratuitious events for full-tree updates as long as the node IDs are stable.
///
/// For unix it's necessary to inform accesskit about any changes to the position or size of the window, hence
/// the `on_event` function that needs calling.
///
/// Similarly, when the window adapter is informed about a focus change, handle_focus_change must be called.
/// Finally, when a component is destroyed, `unregister_item_tree` must be called, which rebuilds the entire
/// tree at the moment.
///
/// If we wanted to move this to corelib, `on_event` gets replaced with listening to the events sent from the
/// platform adapter to the slint::Window. `handle_focus_change` is already internal to WindowInner, as well
/// as `component_destroyed`. The `WindowInner` would own this `AccessKit`.
pub struct AccessKitAdapter {
    inner: accesskit_winit::Adapter,
    window_adapter_weak: Weak<WinitWindowAdapter>,

    node_classes: RefCell<accesskit::NodeClassSet>,
    next_component_id: Cell<u32>,
    components_by_id: RefCell<HashMap<u32, ItemTreeWeak>>,
    component_ids: RefCell<HashMap<NonNull<u8>, u32>>,
    all_nodes: RefCell<Vec<CachedNode>>,
    root_node_id: Cell<NodeId>,
    global_property_tracker: Pin<Box<PropertyTracker<AccessibilitiesPropertyTracker>>>,
}

impl AccessKitAdapter {
    pub fn new(
        window_adapter_weak: Weak<WinitWindowAdapter>,
        winit_window: &winit::window::Window,
    ) -> Self {
        let window_id = winit_window.id();
        let ui_thread_id = std::thread::current().id();
        Self {
            inner: accesskit_winit::Adapter::with_action_handler(
                winit_window,
                move || Self::build_initial_tree(window_id, ui_thread_id),
                Box::new(ActionForwarder::new(window_id)),
            ),
            window_adapter_weak: window_adapter_weak.clone(),
            node_classes: RefCell::new(accesskit::NodeClassSet::new()),
            next_component_id: Cell::new(1),
            components_by_id: Default::default(),
            component_ids: Default::default(),
            all_nodes: Default::default(),
            global_property_tracker: Box::pin(PropertyTracker::new_with_dirty_handler(
                AccessibilitiesPropertyTracker { window_adapter_weak: window_adapter_weak.clone() },
            )),
            root_node_id: Cell::new(NodeId(0)),
        }
    }

    pub fn process_event(&self, window: &winit::window::Window, event: &winit::event::WindowEvent) {
        if matches!(event, winit::event::WindowEvent::Focused(_)) {
            self.global_property_tracker.set_dirty();
            let win = self.window_adapter_weak.clone();
            i_slint_core::timers::Timer::single_shot(Default::default(), move || {
                if let Some(window_adapter) = win.upgrade() {
                    window_adapter.accesskit_adapter.rebuild_tree_of_dirty_nodes();
                };
            });
        }
        self.inner.process_event(window, event);
    }

    pub fn handle_focus_item_change(&self) {
        self.inner.update_if_active(|| TreeUpdate {
            nodes: vec![],
            tree: None,
            focus: self.focus_node(),
        })
    }

    fn focus_node(&self) -> NodeId {
        self.window_adapter_weak
            .upgrade()
            .filter(|window_adapter| window_adapter.winit_window().has_focus())
            .and_then(|window_adapter| {
                let window_inner = WindowInner::from_pub(window_adapter.window());
                window_inner
                    .focus_item
                    .borrow()
                    .upgrade()
                    .or_else(|| {
                        window_inner
                            .try_component()
                            .map(|component_rc| ItemRc::new(component_rc, 0))
                    })
                    .and_then(|focus_item| self.find_node_id_by_item_rc(focus_item))
            })
            .unwrap_or_else(|| self.root_node_id.get())
    }

    fn handle_request(&self, request: ActionRequest) {
        let Some(window_adapter) = self.window_adapter_weak.upgrade() else { return };
        if request.action == Action::Focus {
            if let Some(item) = self.item_rc_for_node_id(request.target) {
                WindowInner::from_pub(window_adapter.window()).set_focus_item(&item);
            }
        }
    }

    pub fn register_item_tree(&self) {
        let win = self.window_adapter_weak.clone();
        i_slint_core::timers::Timer::single_shot(Default::default(), move || {
            if let Some(window_adapter) = win.upgrade() {
                let self_ = &window_adapter.accesskit_adapter;
                self_.inner.update_if_active(|| self_.build_new_tree())
            };
        });
    }

    pub fn unregister_item_tree(&self, component: ItemTreeRef) {
        let component_ptr = ItemTreeRef::as_ptr(component);
        if let Some(component_id) = self.component_ids.borrow_mut().remove(&component_ptr) {
            self.components_by_id.borrow_mut().remove(&component_id);
        }

        let win = self.window_adapter_weak.clone();
        i_slint_core::timers::Timer::single_shot(Default::default(), move || {
            if let Some(window_adapter) = win.upgrade() {
                let self_ = &window_adapter.accesskit_adapter;
                self_.inner.update_if_active(|| self_.build_new_tree())
            };
        });
    }

    fn item_rc_for_node_id(&self, id: NodeId) -> Option<ItemRc> {
        let component_id: u32 = (id.0 >> u32::BITS) as _;
        let index: u32 = (id.0 & u32::MAX as u64) as _;
        let component = self.components_by_id.borrow().get(&component_id)?.upgrade()?;
        Some(ItemRc::new(component, index))
    }

    fn find_node_id_by_item_rc(&self, mut item: ItemRc) -> Option<NodeId> {
        while !item.is_accessible() {
            if let Some(parent) = item.parent_item() {
                item = parent;
            } else {
                break;
            }
        }

        self.encode_item_node_id(&item)
    }

    fn encode_item_node_id(&self, item: &ItemRc) -> Option<NodeId> {
        let component = item.item_tree();
        let component_ptr = ItemTreeRef::as_ptr(ItemTreeRc::borrow(component));
        let component_id = *(self.component_ids.borrow().get(&component_ptr)?);
        let index = item.index();
        Some(NodeId((component_id as u64) << u32::BITS | (index as u64 & u32::MAX as u64)))
    }

    fn rebuild_tree_of_dirty_nodes(&self) {
        if !self.global_property_tracker.is_dirty() {
            return;
        }

        // It's possible that we may have been triggered by a timer, but in the meantime
        // the node tree has been emptied due to a tree structure change.
        if self.all_nodes.borrow().is_empty() {
            return;
        }

        let Some(window_adapter) = self.window_adapter_weak.upgrade() else { return };
        let window = window_adapter.window();

        self.inner.update_if_active(|| {
            self.global_property_tracker.as_ref().evaluate_as_dependency_root(|| {
                let all_nodes = self.all_nodes.borrow();
                let nodes = all_nodes.iter().filter_map(|cached_node| {
                    cached_node.tracker.as_ref().evaluate_if_dirty(|| {
                        let scale_factor = ScaleFactor::new(window.scale_factor());
                        let item = self.item_rc_for_node_id(cached_node.id)?;

                        let mut builder = self.build_node_without_children(&item, scale_factor);

                        builder.set_children(cached_node.children.clone());

                        let node = builder.build(&mut self.node_classes.borrow_mut());

                        Some((cached_node.id, node))
                    })?
                });

                TreeUpdate { nodes: nodes.collect(), tree: None, focus: self.focus_node() }
            })
        })
    }

    fn build_node_for_item_recursively(
        &self,
        item: ItemRc,
        nodes: &mut Vec<(NodeId, Node)>,
        scale_factor: ScaleFactor,
    ) -> NodeId {
        let tracker = Box::pin(PropertyTracker::default());

        let mut builder =
            tracker.as_ref().evaluate(|| self.build_node_without_children(&item, scale_factor));

        let children = i_slint_core::accessibility::accessible_descendents(&item)
            .map(|child| self.build_node_for_item_recursively(child, nodes, scale_factor))
            .collect::<Vec<NodeId>>();

        builder.set_children(children.clone());

        let component = item.item_tree();
        let component_ptr = ItemTreeRef::as_ptr(ItemTreeRc::borrow(component));
        if !self.component_ids.borrow().contains_key(&component_ptr) {
            let component_id = self.next_component_id.get();
            self.next_component_id.set(component_id + 1);
            self.component_ids.borrow_mut().insert(component_ptr, component_id);
            self.components_by_id
                .borrow_mut()
                .insert(component_id, ItemTreeRc::downgrade(component));
        }

        let id = self.encode_item_node_id(&item).unwrap();
        self.all_nodes.borrow_mut().push(CachedNode { id, children, tracker });
        let node = builder.build(&mut self.node_classes.borrow_mut());

        nodes.push((id, node));

        id
    }

    fn build_new_tree(&self) -> TreeUpdate {
        let Some(window_adapter) = self.window_adapter_weak.upgrade() else {
            return TreeUpdate {
                nodes: Default::default(),
                tree: Default::default(),
                focus: self.root_node_id.get(),
            };
        };
        let window = window_adapter.window();
        let window_inner = i_slint_core::window::WindowInner::from_pub(window);

        let root_item = ItemRc::new(window_inner.component(), 0);

        self.all_nodes.borrow_mut().clear();
        let mut nodes = Vec::new();

        let root_id = self.global_property_tracker.as_ref().evaluate_as_dependency_root(|| {
            self.build_node_for_item_recursively(
                root_item,
                &mut nodes,
                ScaleFactor::new(window.scale_factor()),
            )
        });
        self.root_node_id.set(root_id);

        TreeUpdate { nodes, tree: Some(Tree::new(root_id)), focus: self.focus_node() }
    }

    fn build_initial_tree(
        window_id: winit::window::WindowId,
        ui_thread_id: std::thread::ThreadId,
    ) -> TreeUpdate {
        if std::thread::current().id() == ui_thread_id {
            return crate::event_loop::window_by_id(window_id)
                .map(|adapter| adapter.accesskit_adapter.build_new_tree())
                .unwrap_or_else(|| {
                    // We failed to upgrade the Weak window adapter despite being called in the mean thread. That means
                    // we're trying to build the initial tree while the window adapter is still being constructed. Report
                    // a dummy tree and schedule a rebuild later.

                    i_slint_core::timers::Timer::single_shot(Default::default(), move || {
                        if let Some(window_adapter) = crate::event_loop::window_by_id(window_id) {
                            let self_ = &window_adapter.accesskit_adapter;
                            self_.inner.update_if_active(|| self_.build_new_tree())
                        };
                    });

                    let dummy_node_id = NodeId(0);
                    TreeUpdate {
                        nodes: vec![(
                            dummy_node_id,
                            NodeBuilder::new(Role::Window).build(&mut Default::default()),
                        )],
                        tree: Some(Tree::new(dummy_node_id)),
                        focus: dummy_node_id,
                    }
                });
        }

        let update_from_main_thread = Arc::new((Mutex::new(None), Condvar::new()));
        let update_result = i_slint_core::api::invoke_from_event_loop({
            let update_from_main_thread = update_from_main_thread.clone();
            move || {
                let (lock, wait_condition) = &*update_from_main_thread;
                let mut update = lock.lock().unwrap();

                *update = Some(Self::build_initial_tree(window_id, ui_thread_id));

                wait_condition.notify_one();
            }
        });

        if update_result.is_err() {
            // If we're having trouble calling `invoke_from_event_loop` then the event loop is probably
            // dead. Fall back to returning a dummy tree.
            let dummy_node_id = NodeId(0);
            return TreeUpdate {
                nodes: vec![(
                    dummy_node_id,
                    NodeBuilder::new(Role::Window).build(&mut Default::default()),
                )],
                tree: Some(Tree::new(dummy_node_id)),
                focus: dummy_node_id,
            };
        }

        let (lock, wait_condition) = &*update_from_main_thread;
        let mut update = lock.lock().unwrap();
        while update.is_none() {
            update = wait_condition.wait(update).unwrap();
        }

        update.take().unwrap()
    }

    fn build_node_without_children(&self, item: &ItemRc, scale_factor: ScaleFactor) -> NodeBuilder {
        let (role, label) = if let Some(window_item) = item.downcast::<WindowItem>() {
            (Role::Window, window_item.as_pin_ref().title().to_string())
        } else {
            (
                match item.accessible_role() {
                    i_slint_core::items::AccessibleRole::None => Role::Unknown,
                    i_slint_core::items::AccessibleRole::Button => Role::Button,
                    i_slint_core::items::AccessibleRole::Checkbox => Role::CheckBox,
                    i_slint_core::items::AccessibleRole::Combobox => Role::ComboBox,
                    i_slint_core::items::AccessibleRole::Slider => Role::Slider,
                    i_slint_core::items::AccessibleRole::Spinbox => Role::SpinButton,
                    i_slint_core::items::AccessibleRole::Tab => Role::Tab,
                    i_slint_core::items::AccessibleRole::Text => Role::StaticText,
                    i_slint_core::items::AccessibleRole::ProgressIndicator => {
                        Role::ProgressIndicator
                    }
                },
                item.accessible_string_property(
                    i_slint_core::accessibility::AccessibleStringProperty::Label,
                )
                .to_string(),
            )
        };

        let mut builder = NodeBuilder::new(role);

        builder.set_name(label);

        let geometry = item.geometry();
        let absolute_origin = item.map_to_window(geometry.origin);
        let physical_origin = (absolute_origin * scale_factor).cast::<f64>();
        let physical_size = (geometry.size * scale_factor).cast::<f64>();
        builder.set_bounds(accesskit::Rect {
            x0: physical_origin.x,
            y0: physical_origin.y,
            x1: physical_origin.x + physical_size.width,
            y1: physical_origin.y + physical_size.height,
        });

        if item.accessible_string_property(AccessibleStringProperty::Checkable) == "true" {
            builder.set_checked(
                if item.accessible_string_property(AccessibleStringProperty::Checked) == "true" {
                    Checked::True
                } else {
                    Checked::False
                },
            );
        }

        builder.set_description(
            item.accessible_string_property(AccessibleStringProperty::Description).to_string(),
        );

        if matches!(
            role,
            Role::Button
                | Role::CheckBox
                | Role::ComboBox
                | Role::Slider
                | Role::SpinButton
                | Role::Tab
        ) {
            builder.add_action(Action::Focus);
        }

        let min = item.accessible_string_property(AccessibleStringProperty::ValueMinimum);
        let max = item.accessible_string_property(AccessibleStringProperty::ValueMaximum);
        let step = item.accessible_string_property(AccessibleStringProperty::ValueStep);
        let value = item.accessible_string_property(AccessibleStringProperty::Value).to_string();

        match (min.parse(), max.parse(), value.parse(), step.parse()) {
            (Ok(min), Ok(max), Ok(value), Ok(step)) => {
                builder.set_min_numeric_value(min);
                builder.set_max_numeric_value(max);
                builder.set_numeric_value(value);
                builder.set_numeric_value_step(step);
            }
            _ => {
                builder.set_value(value);
            }
        }

        builder
    }
}

struct AccessibilitiesPropertyTracker {
    window_adapter_weak: Weak<WinitWindowAdapter>,
}

impl i_slint_core::properties::PropertyDirtyHandler for AccessibilitiesPropertyTracker {
    fn notify(&self) {
        let win = self.window_adapter_weak.clone();
        i_slint_core::timers::Timer::single_shot(Default::default(), move || {
            if let Some(window_adapter) = win.upgrade() {
                window_adapter.accesskit_adapter.rebuild_tree_of_dirty_nodes();
            };
        })
    }
}

struct CachedNode {
    id: NodeId,
    children: Vec<NodeId>,
    tracker: Pin<Box<PropertyTracker>>,
}

struct ActionForwarder {
    window_id: winit::window::WindowId,
}

impl ActionForwarder {
    pub fn new(window_id: winit::window::WindowId) -> Self {
        Self { window_id }
    }
}

impl accesskit::ActionHandler for ActionForwarder {
    fn do_action(&mut self, request: ActionRequest) {
        let window_id = self.window_id;
        i_slint_core::api::invoke_from_event_loop(move || {
            let Some(window_adapter) = crate::event_loop::window_by_id(window_id) else {
                return;
            };
            window_adapter.accesskit_adapter.handle_request(request)
        })
        .ok();
    }
}