Integrate AccessKit (#6874)

# Objective

UIs created for Bevy cannot currently be made accessible. This PR aims to address that.

## Solution

Integrate AccessKit as a dependency, adding accessibility support to existing bevy_ui widgets.

## Changelog

### Added

* Integrate with and expose [AccessKit](https://accesskit.dev) for platform accessibility.
* Add `Label` for marking text specifically as a label for UI controls.

Cargo.toml

@@ -209,6 +209,10 @@ detailed_trace = ["bevy_internal/detailed_trace"]
 # Include tonemapping Look Up Tables KTX2 files
 tonemapping_luts = ["bevy_internal/tonemapping_luts"]
 
+# Enable AccessKit on Unix backends (currently only works with experimental
+# screen readers and forks.)
+accesskit_unix = ["bevy_internal/accesskit_unix"]
+
 [dependencies]
 bevy_dylib = { path = "crates/bevy_dylib", version = "0.9.0", default-features = false, optional = true }
 bevy_internal = { path = "crates/bevy_internal", version = "0.9.0", default-features = false }

crates/bevy_a11y/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "bevy_a11y"
+version = "0.9.0"
+edition = "2021"
+description = "Provides accessibility support for Bevy Engine"
+homepage = "https://bevyengine.org"
+repository = "https://github.com/bevyengine/bevy"
+license = "MIT OR Apache-2.0"
+keywords = ["bevy", "accessibility", "a11y"]
+
+[dependencies]
+# bevy
+bevy_app = { path = "../bevy_app", version = "0.9.0" }
+bevy_derive = { path = "../bevy_derive", version = "0.9.0" }
+bevy_ecs = { path = "../bevy_ecs", version = "0.9.0" }
+
+accesskit = "0.10"

crates/bevy_a11y/src/lib.rs

@@ -0,0 +1,70 @@
+//! Accessibility for Bevy
+
+#![warn(missing_docs)]
+#![forbid(unsafe_code)]
+
+use std::{
+    num::NonZeroU128,
+    sync::{atomic::AtomicBool, Arc},
+};
+
+pub use accesskit;
+use accesskit::{NodeBuilder, NodeId};
+use bevy_app::Plugin;
+use bevy_derive::{Deref, DerefMut};
+use bevy_ecs::{
+    prelude::{Component, Entity},
+    system::Resource,
+};
+
+/// Resource that tracks whether an assistive technology has requested
+/// accessibility information.
+///
+/// Useful if a third-party plugin needs to conditionally integrate with
+/// `AccessKit`
+#[derive(Resource, Default, Clone, Debug, Deref, DerefMut)]
+pub struct AccessibilityRequested(Arc<AtomicBool>);
+
+/// Component to wrap a [`accesskit::Node`], representing this entity to the platform's
+/// accessibility API.
+///
+/// If an entity has a parent, and that parent also has an `AccessibilityNode`,
+/// the entity's node will be a child of the parent's node.
+///
+/// If the entity doesn't have a parent, or if the immediate parent doesn't have
+/// an `AccessibilityNode`, its node will be an immediate child of the primary window.
+#[derive(Component, Clone, Deref, DerefMut)]
+pub struct AccessibilityNode(pub NodeBuilder);
+
+impl From<NodeBuilder> for AccessibilityNode {
+    fn from(node: NodeBuilder) -> Self {
+        Self(node)
+    }
+}
+
+/// Extensions to ease integrating entities with [`AccessKit`](https://accesskit.dev).
+pub trait AccessKitEntityExt {
+    /// Convert an entity to a stable [`NodeId`].
+    fn to_node_id(&self) -> NodeId;
+}
+
+impl AccessKitEntityExt for Entity {
+    fn to_node_id(&self) -> NodeId {
+        let id = NonZeroU128::new(self.to_bits() as u128 + 1);
+        NodeId(id.unwrap())
+    }
+}
+
+/// Resource representing which entity has keyboard focus, if any.
+#[derive(Resource, Default, Deref, DerefMut)]
+pub struct Focus(Option<Entity>);
+
+/// Plugin managing non-GUI aspects of integrating with accessibility APIs.
+pub struct AccessibilityPlugin;
+
+impl Plugin for AccessibilityPlugin {
+    fn build(&self, app: &mut bevy_app::App) {
+        app.init_resource::<AccessibilityRequested>()
+            .init_resource::<Focus>();
+    }
+}

crates/bevy_internal/Cargo.toml

@@ -82,10 +82,15 @@ dynamic_linking = ["bevy_diagnostic/dynamic_linking"]
 # Enable using a shared stdlib for cxx on Android.
 android_shared_stdcxx = ["bevy_audio/android_shared_stdcxx"]
 
+# Enable AccessKit on Unix backends (currently only works with experimental
+# screen readers and forks.)
+accesskit_unix = ["bevy_winit/accesskit_unix"]
+
 bevy_text = ["dep:bevy_text", "bevy_ui?/bevy_text"]
 
 [dependencies]
 # bevy
+bevy_a11y = { path = "../bevy_a11y", version = "0.9.0" }
 bevy_app = { path = "../bevy_app", version = "0.9.0" }
 bevy_core = { path = "../bevy_core", version = "0.9.0" }
 bevy_derive = { path = "../bevy_derive", version = "0.9.0" }

crates/bevy_internal/src/default_plugins.rs

@@ -50,7 +50,8 @@ impl PluginGroup for DefaultPlugins {
             .add(bevy_hierarchy::HierarchyPlugin::default())
             .add(bevy_diagnostic::DiagnosticsPlugin::default())
             .add(bevy_input::InputPlugin::default())
-            .add(bevy_window::WindowPlugin::default());
+            .add(bevy_window::WindowPlugin::default())
+            .add(bevy_a11y::AccessibilityPlugin);
 
         #[cfg(feature = "bevy_asset")]
         {

crates/bevy_internal/src/lib.rs

@@ -7,6 +7,11 @@ pub mod prelude;
 mod default_plugins;
 pub use default_plugins::*;
 
+pub mod a11y {
+    //! Integrate with platform accessibility APIs.
+    pub use bevy_a11y::*;
+}
+
 pub mod app {
     //! Build bevy apps, create plugins, and read events.
     pub use bevy_app::*;

crates/bevy_ui/Cargo.toml

@@ -10,6 +10,7 @@ keywords = ["bevy"]
 
 [dependencies]
 # bevy
+bevy_a11y = { path = "../bevy_a11y", version = "0.9.0" }
 bevy_app = { path = "../bevy_app", version = "0.9.0" }
 bevy_asset = { path = "../bevy_asset", version = "0.9.0" }
 bevy_core_pipeline = { path = "../bevy_core_pipeline", version = "0.9.0" }

crates/bevy_ui/src/accessibility.rs

@@ -0,0 +1,157 @@
+use bevy_a11y::{
+    accesskit::{NodeBuilder, Rect, Role},
+    AccessibilityNode,
+};
+use bevy_app::{App, Plugin};
+
+use bevy_ecs::{
+    prelude::Entity,
+    query::{Changed, Or, Without},
+    system::{Commands, Query},
+};
+use bevy_hierarchy::Children;
+
+use bevy_render::prelude::Camera;
+use bevy_text::Text;
+use bevy_transform::prelude::GlobalTransform;
+
+use crate::{
+    prelude::{Button, Label},
+    Node, UiImage,
+};
+
+fn calc_name(texts: &Query<&Text>, children: &Children) -> Option<Box<str>> {
+    let mut name = None;
+    for child in children.iter() {
+        if let Ok(text) = texts.get(*child) {
+            let values = text
+                .sections
+                .iter()
+                .map(|v| v.value.to_string())
+                .collect::<Vec<String>>();
+            name = Some(values.join(" "));
+        }
+    }
+    name.map(|v| v.into_boxed_str())
+}
+
+fn calc_bounds(
+    camera: Query<(&Camera, &GlobalTransform)>,
+    mut nodes: Query<
+        (&mut AccessibilityNode, &Node, &GlobalTransform),
+        Or<(Changed<Node>, Changed<GlobalTransform>)>,
+    >,
+) {
+    if let Ok((camera, camera_transform)) = camera.get_single() {
+        for (mut accessible, node, transform) in &mut nodes {
+            if let Some(translation) =
+                camera.world_to_viewport(camera_transform, transform.translation())
+            {
+                let bounds = Rect::new(
+                    translation.x.into(),
+                    translation.y.into(),
+                    (translation.x + node.calculated_size.x).into(),
+                    (translation.y + node.calculated_size.y).into(),
+                );
+                accessible.set_bounds(bounds);
+            }
+        }
+    }
+}
+
+fn button_changed(
+    mut commands: Commands,
+    mut query: Query<(Entity, &Children, Option<&mut AccessibilityNode>), Changed<Button>>,
+    texts: Query<&Text>,
+) {
+    for (entity, children, accessible) in &mut query {
+        let name = calc_name(&texts, children);
+        if let Some(mut accessible) = accessible {
+            accessible.set_role(Role::Button);
+            if let Some(name) = name {
+                accessible.set_name(name);
+            } else {
+                accessible.clear_name();
+            }
+        } else {
+            let mut node = NodeBuilder::new(Role::Button);
+            if let Some(name) = name {
+                node.set_name(name);
+            }
+            commands
+                .entity(entity)
+                .insert(AccessibilityNode::from(node));
+        }
+    }
+}
+
+fn image_changed(
+    mut commands: Commands,
+    mut query: Query<
+        (Entity, &Children, Option<&mut AccessibilityNode>),
+        (Changed<UiImage>, Without<Button>),
+    >,
+    texts: Query<&Text>,
+) {
+    for (entity, children, accessible) in &mut query {
+        let name = calc_name(&texts, children);
+        if let Some(mut accessible) = accessible {
+            accessible.set_role(Role::Image);
+            if let Some(name) = name {
+                accessible.set_name(name);
+            } else {
+                accessible.clear_name();
+            }
+        } else {
+            let mut node = NodeBuilder::new(Role::Image);
+            if let Some(name) = name {
+                node.set_name(name);
+            }
+            commands
+                .entity(entity)
+                .insert(AccessibilityNode::from(node));
+        }
+    }
+}
+
+fn label_changed(
+    mut commands: Commands,
+    mut query: Query<(Entity, &Text, Option<&mut AccessibilityNode>), Changed<Label>>,
+) {
+    for (entity, text, accessible) in &mut query {
+        let values = text
+            .sections
+            .iter()
+            .map(|v| v.value.to_string())
+            .collect::<Vec<String>>();
+        let name = Some(values.join(" ").into_boxed_str());
+        if let Some(mut accessible) = accessible {
+            accessible.set_role(Role::LabelText);
+            if let Some(name) = name {
+                accessible.set_name(name);
+            } else {
+                accessible.clear_name();
+            }
+        } else {
+            let mut node = NodeBuilder::new(Role::LabelText);
+            if let Some(name) = name {
+                node.set_name(name);
+            }
+            commands
+                .entity(entity)
+                .insert(AccessibilityNode::from(node));
+        }
+    }
+}
+
+/// `AccessKit` integration for `bevy_ui`.
+pub(crate) struct AccessibilityPlugin;
+
+impl Plugin for AccessibilityPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_system(calc_bounds)
+            .add_system(button_changed)
+            .add_system(image_changed)
+            .add_system(label_changed);
+    }
+}

crates/bevy_ui/src/lib.rs

@@ -9,6 +9,7 @@ mod render;
 mod stack;
 mod ui_node;
 
+mod accessibility;
 pub mod camera_config;
 pub mod node_bundles;
 pub mod update;
@@ -27,8 +28,7 @@ pub use ui_node::*;
 pub mod prelude {
     #[doc(hidden)]
     pub use crate::{
-        camera_config::*, geometry::*, node_bundles::*, ui_node::*, widget::Button, Interaction,
-        UiScale,
+        camera_config::*, geometry::*, node_bundles::*, ui_node::*, widget::*, Interaction, UiScale,
     };
 }
 
@@ -102,6 +102,8 @@ impl Plugin for UiPlugin {
             .register_type::<UiImage>()
             .register_type::<Val>()
             .register_type::<widget::Button>()
+            .register_type::<widget::Label>()
+            .add_plugin(accessibility::AccessibilityPlugin)
             .configure_set(UiSystem::Focus.in_base_set(CoreSet::PreUpdate))
             .configure_set(UiSystem::Flex.in_base_set(CoreSet::PostUpdate))
             .configure_set(UiSystem::Stack.in_base_set(CoreSet::PostUpdate))

crates/bevy_ui/src/widget/label.rs

@@ -0,0 +1,9 @@
+use bevy_ecs::prelude::Component;
+use bevy_ecs::reflect::ReflectComponent;
+use bevy_reflect::std_traits::ReflectDefault;
+use bevy_reflect::Reflect;
+
+/// Marker struct for labels
+#[derive(Component, Debug, Default, Clone, Copy, Reflect)]
+#[reflect(Component, Default)]
+pub struct Label;

crates/bevy_ui/src/widget/mod.rs

@@ -2,10 +2,12 @@
 
 mod button;
 mod image;
+mod label;
 #[cfg(feature = "bevy_text")]
 mod text;
 
 pub use button::*;
 pub use image::*;
+pub use label::*;
 #[cfg(feature = "bevy_text")]
 pub use text::*;

crates/bevy_winit/Cargo.toml

@@ -12,18 +12,23 @@ keywords = ["bevy"]
 trace = []
 wayland = ["winit/wayland"]
 x11 = ["winit/x11"]
+accesskit_unix = ["accesskit_winit/accesskit_unix"]
 
 [dependencies]
 # bevy
+bevy_a11y = { path = "../bevy_a11y", version = "0.9.0" }
 bevy_app = { path = "../bevy_app", version = "0.9.0" }
+bevy_derive = { path = "../bevy_derive", version = "0.9.0" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.9.0" }
+bevy_hierarchy = { path = "../bevy_hierarchy", version = "0.9.0" }
 bevy_input = { path = "../bevy_input", version = "0.9.0" }
 bevy_math = { path = "../bevy_math", version = "0.9.0" }
 bevy_window = { path = "../bevy_window", version = "0.9.0" }
 bevy_utils = { path = "../bevy_utils", version = "0.9.0" }
 
 # other
 winit = { version = "0.28", default-features = false }
+accesskit_winit = { version = "0.12", default-features = false }
 approx = { version = "0.5", default-features = false }
 raw-window-handle = "0.5"