Remove dependency on tts (#3651)

We were using [`tts`](https://github.com/ndarilek/tts-rs) for the
web-only screen reader. This was overkill, to say the least. It is now
replaced with ten lines of `web-sys` calls.

crates/eframe/src/web/app_runner.rs

@@ -13,7 +13,6 @@ pub struct AppRunner {
     app: Box<dyn epi::App>,
     pub(crate) needs_repaint: std::sync::Arc<NeedRepaint>,
     last_save_time: f64,
-    screen_reader: super::screen_reader::ScreenReader,
     pub(crate) text_cursor_pos: Option<egui::Pos2>,
     pub(crate) mutable_text_under_cursor: bool,
 
@@ -113,7 +112,6 @@ impl AppRunner {
             app,
             needs_repaint,
             last_save_time: now_sec(),
-            screen_reader: Default::default(),
             text_cursor_pos: None,
             mutable_text_under_cursor: false,
             textures_delta: Default::default(),
@@ -235,9 +233,9 @@ impl AppRunner {
     }
 
     fn handle_platform_output(&mut self, platform_output: egui::PlatformOutput) {
+        #[cfg(feature = "web_screen_reader")]
         if self.egui_ctx.options(|o| o.screen_reader) {
-            self.screen_reader
-                .speak(&platform_output.events_description());
+            super::screen_reader::speak(&platform_output.events_description());
         }
 
         let egui::PlatformOutput {

crates/eframe/src/web/mod.rs

@@ -12,6 +12,7 @@ mod web_logger;
 mod web_runner;
 
 /// Access to the browser screen reader.
+#[cfg(feature = "web_screen_reader")]
 pub mod screen_reader;
 
 /// Access to local browser storage.

crates/eframe/src/web/screen_reader.rs

@@ -1,51 +1,20 @@
-/// Screen reader support.
-pub struct ScreenReader {
-    #[cfg(feature = "tts")]
-    tts: Option<tts::Tts>,
-}
-
-#[cfg(not(feature = "tts"))]
-#[allow(clippy::derivable_impls)] // False positive
-impl Default for ScreenReader {
-    fn default() -> Self {
-        Self {}
+/// Speak the given text out loud.
+pub fn speak(text: &str) {
+    if text.is_empty() {
+        return;
     }
-}
 
-#[cfg(feature = "tts")]
-impl Default for ScreenReader {
-    fn default() -> Self {
-        let tts = match tts::Tts::default() {
-            Ok(screen_reader) => {
-                log::debug!("Initialized screen reader.");
-                Some(screen_reader)
-            }
-            Err(err) => {
-                log::warn!("Failed to load screen reader: {}", err);
-                None
-            }
-        };
-        Self { tts }
-    }
-}
+    if let Some(window) = web_sys::window() {
+        log::debug!("Speaking {text:?}");
 
-impl ScreenReader {
-    /// Speak the given text out loud.
-    #[cfg(not(feature = "tts"))]
-    #[allow(clippy::unused_self)]
-    pub fn speak(&mut self, _text: &str) {}
+        if let Ok(speech_synthesis) = window.speech_synthesis() {
+            speech_synthesis.cancel(); // interrupt previous speech, if any
 
-    /// Speak the given text out loud.
-    #[cfg(feature = "tts")]
-    pub fn speak(&mut self, text: &str) {
-        if text.is_empty() {
-            return;
-        }
-        if let Some(tts) = &mut self.tts {
-            log::debug!("Speaking: {:?}", text);
-            let interrupt = true;
-            if let Err(err) = tts.speak(text, interrupt) {
-                log::warn!("Failed to read: {}", err);
+            if let Ok(utterance) = web_sys::SpeechSynthesisUtterance::new_with_text(text) {
+                utterance.set_rate(1.0);
+                utterance.set_pitch(1.0);
+                utterance.set_volume(1.0);
+                speech_synthesis.speak(&utterance);
             }
         }
     }