Implement accessibility APIs via AccessKit (#2294)

* squash before rebase

* Update AccessKit, introducing support for editable spinners on Windows and an important fix for navigation order on macOS

* Restore support for increment and decrement actions in DragValue

* Avoid VoiceOver race condition bug

* fix clippy lint

* Tell AccessKit that the default action for a text edit (equivalent to a click) is to set the focus. This matters to some platform adapters.

* Refactor InputState functions for AccessKit actions

* Support the AccessKit SetValue for DragValue; this is the only way for a Windows AT to programmatically adjust the value

* Same for Slider

* Properly associate the slider label with both the slider and the drag value

* Lazily activate egui's AccessKit support

* fix clippy lint

* Update AccessKit

* More documentation, particularly around lazy activation

* Tweak one of the doc comments

* See if I can get AccessKit exempted from the 'missing backticks' lint

* Make PlatformOutput::accesskit_update an Option

* Refactor lazy activation

* Refactor node mutation (again)

* Eliminate the need for an explicit is_accesskit_active method, at least for now

* Fix doc comment

* More refactoring of tree construction; don't depend on Arc::get_mut

* Override a clippy lint; I seem to have no other choice

* Final planned refactor: a more flexible approach to hierarchy

* Last AccessKit update for this PR; includes an important macOS DPI fix

* Move and document the optional accesskit dependency

* Fix comment typo

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* reformat

* More elegant code for conditionally creating a node

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

* Set step to 1.0 for all integer sliders

* Add doc example for Response::labelled_by

* Clarify a TODO comment I left for myself

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

CHANGELOG.md

@@ -24,6 +24,7 @@ NOTE: [`epaint`](crates/epaint/CHANGELOG.md), [`eframe`](crates/eframe/CHANGELOG
 * Added `Area::constrain` and `Window::constrain` which constrains area to the screen bounds. ([#2270](https://github.com/emilk/egui/pull/2270)).
 * Added `Area::pivot` and `Window::pivot` which controls what part of the window to position. ([#2303](https://github.com/emilk/egui/pull/2303)).
 * Added support for [thin space](https://en.wikipedia.org/wiki/Thin_space).
+* Added optional integration with [AccessKit](https://accesskit.dev/) for implementing platform accessibility APIs. ([#2294](https://github.com/emilk/egui/pull/2294)).
 
 ### Changed 🔧
 * Panels always have a separator line, but no stroke on other sides. Their spacing has also changed slightly ([#2261](https://github.com/emilk/egui/pull/2261)).

clippy.toml

@@ -0,0 +1 @@
+doc-valid-idents = ["AccessKit", ".."]

crates/eframe/CHANGELOG.md

@@ -18,6 +18,7 @@ NOTE: [`egui-winit`](../egui-winit/CHANGELOG.md), [`egui_glium`](../egui_glium/C
 * Web: Add `WebInfo::user_agent` ([#2202](https://github.com/emilk/egui/pull/2202)).
 * Wgpu device/adapter/surface creation has now various configuration options exposed via `NativeOptions/WebOptions::wgpu_options` ([#2207](https://github.com/emilk/egui/pull/2207)).
 * Fix: Make sure that `native_pixels_per_point` is updated ([#2256](https://github.com/emilk/egui/pull/2256)).
+* Added optional, but enabled by default, integration with [AccessKit](https://accesskit.dev/) for implementing platform accessibility APIs. ([#2294](https://github.com/emilk/egui/pull/2294)).
 
 
 ## 0.19.0 - 2022-08-20

crates/eframe/Cargo.toml

@@ -20,7 +20,10 @@ all-features = true
 
 
 [features]
-default = ["default_fonts", "glow"]
+default = ["accesskit", "default_fonts", "glow"]
+
+## Enable platform accessibility API implementations through [AccessKit](https://accesskit.dev/).
+accesskit = ["egui/accesskit", "egui-winit/accesskit"]
 
 ## Detect dark mode system preference using [`dark-light`](https://docs.rs/dark-light).
 ##

crates/eframe/src/native/epi_integration.rs

@@ -3,6 +3,10 @@ use winit::event_loop::EventLoopWindowTarget;
 #[cfg(target_os = "macos")]
 use winit::platform::macos::WindowBuilderExtMacOS as _;
 
+#[cfg(feature = "accesskit")]
+use egui::accesskit;
+#[cfg(feature = "accesskit")]
+use egui_winit::accesskit_winit;
 use egui_winit::{native_pixels_per_point, EventResponse, WindowSettings};
 
 use crate::{epi, Theme, WindowInfo};
@@ -262,6 +266,25 @@ impl EpiIntegration {
         }
     }
 
+    #[cfg(feature = "accesskit")]
+    pub fn init_accesskit<E: From<accesskit_winit::ActionRequestEvent> + Send>(
+        &mut self,
+        window: &winit::window::Window,
+        event_loop_proxy: winit::event_loop::EventLoopProxy<E>,
+    ) {
+        let egui_ctx = self.egui_ctx.clone();
+        self.egui_winit
+            .init_accesskit(window, event_loop_proxy, move || {
+                // This function is called when an accessibility client
+                // (e.g. screen reader) makes its first request. If we got here,
+                // we know that an accessibility tree is actually wanted.
+                egui_ctx.enable_accesskit();
+                // Enqueue a repaint so we'll receive a full tree update soon.
+                egui_ctx.request_repaint();
+                egui::accesskit_placeholder_tree_update()
+            });
+    }
+
     pub fn warm_up(&mut self, app: &mut dyn epi::App, window: &winit::window::Window) {
         crate::profile_function!();
         let saved_memory: egui::Memory = self.egui_ctx.memory().clone();
@@ -301,6 +324,11 @@ impl EpiIntegration {
         self.egui_winit.on_event(&self.egui_ctx, event)
     }
 
+    #[cfg(feature = "accesskit")]
+    pub fn on_accesskit_action_request(&mut self, request: accesskit::ActionRequest) {
+        self.egui_winit.on_accesskit_action_request(request);
+    }
+
     pub fn update(
         &mut self,
         app: &mut dyn epi::App,