Remove egui_web and epi (#1545)

* Remove integration name (it is always eframe)

* Remove egui_web crate

* Move egui_web/CHANGELOG.md into eframe/CHANGELOG.md

* Remove all mentions of egui_web

* Remove epi crate and absorb into eframe

* egui_glow: only use puffin on native

* Remove WASM doc from CI (we don't generate it anyways!)

* Remove eframe::epi and improve eframe docs

eframe/src/epi.rs

@@ -0,0 +1,489 @@
+//! Platform-agnostic interface for writing apps using [`egui`] (epi = egui programming interface).
+//!
+//! `epi` provides interfaces for window management and serialization.
+//!
+//! Start by looking at the [`App`] trait, and implement [`App::update`].
+
+#![warn(missing_docs)] // Let's keep `epi` well-documented.
+
+/// This is how your app is created.
+///
+/// You can use the [`CreationContext`] to setup egui, restore state, setup OpenGL things, etc.
+pub type AppCreator = Box<dyn FnOnce(&CreationContext<'_>) -> Box<dyn App>>;
+
+/// Data that is passed to [`AppCreator`] that can be used to setup and initialize your app.
+pub struct CreationContext<'s> {
+    /// The egui Context.
+    ///
+    /// You can use this to customize the look of egui, e.g to call [`egui::Context::set_fonts`],
+    /// [`egui::Context::set_visuals`] etc.
+    pub egui_ctx: egui::Context,
+
+    /// Information about the surrounding environment.
+    pub integration_info: IntegrationInfo,
+
+    /// You can use the storage to restore app state(requires the "persistence" feature).
+    pub storage: Option<&'s dyn Storage>,
+
+    /// The [`glow::Context`] allows you to initialize OpenGL resources (e.g. shaders) that
+    /// you might want to use later from a [`egui::PaintCallback`].
+    pub gl: std::rc::Rc<glow::Context>,
+}
+
+// ----------------------------------------------------------------------------
+
+/// Implement this trait to write apps that can be compiled for both web/wasm and desktop/native using [`eframe`](https://github.com/emilk/egui/tree/master/eframe).
+pub trait App {
+    /// Called each time the UI needs repainting, which may be many times per second.
+    ///
+    /// Put your widgets into a [`egui::SidePanel`], [`egui::TopBottomPanel`], [`egui::CentralPanel`], [`egui::Window`] or [`egui::Area`].
+    ///
+    /// The [`egui::Context`] can be cloned and saved if you like.
+    ///
+    /// To force a repaint, call [`egui::Context::request_repaint`] at any time (e.g. from another thread).
+    fn update(&mut self, ctx: &egui::Context, frame: &mut Frame);
+
+    /// Called on shutdown, and perhaps at regular intervals. Allows you to save state.
+    ///
+    /// Only called when the "persistence" feature is enabled.
+    ///
+    /// On web the state is stored to "Local Storage".
+    /// On native the path is picked using [`directories_next::ProjectDirs::data_dir`](https://docs.rs/directories-next/2.0.0/directories_next/struct.ProjectDirs.html#method.data_dir) which is:
+    /// * Linux:   `/home/UserName/.local/share/APPNAME`
+    /// * macOS:   `/Users/UserName/Library/Application Support/APPNAME`
+    /// * Windows: `C:\Users\UserName\AppData\Roaming\APPNAME`
+    ///
+    /// where `APPNAME` is what is given to `eframe::run_native`.
+    fn save(&mut self, _storage: &mut dyn Storage) {}
+
+    /// Called before an exit that can be aborted.
+    /// By returning `false` the exit will be aborted. To continue the exit return `true`.
+    ///
+    /// A scenario where this method will be run is after pressing the close button on a native
+    /// window, which allows you to ask the user whether they want to do something before exiting.
+    /// See the example at <https://github.com/emilk/egui/blob/master/examples/confirm_exit/> for practical usage.
+    ///
+    /// It will _not_ be called on the web or when the window is forcefully closed.
+    fn on_exit_event(&mut self) -> bool {
+        true
+    }
+
+    /// Called once on shutdown, after [`Self::save`].
+    ///
+    /// If you need to abort an exit use [`Self::on_exit_event`].
+    fn on_exit(&mut self, _gl: &glow::Context) {}
+
+    // ---------
+    // Settings:
+
+    /// Time between automatic calls to [`Self::save`]
+    fn auto_save_interval(&self) -> std::time::Duration {
+        std::time::Duration::from_secs(30)
+    }
+
+    /// The size limit of the web app canvas.
+    ///
+    /// By default the max size is [`egui::Vec2::INFINITY`], i.e. unlimited.
+    ///
+    /// A large canvas can lead to bad frame rates on some older browsers on some platforms
+    /// (see <https://bugzilla.mozilla.org/show_bug.cgi?id=1010527#c0>).
+    fn max_size_points(&self) -> egui::Vec2 {
+        egui::Vec2::INFINITY
+    }
+
+    /// Background color for the app, e.g. what is sent to `gl.clearColor`.
+    /// This is the background of your windows if you don't set a central panel.
+    fn clear_color(&self) -> egui::Rgba {
+        // NOTE: a bright gray makes the shadows of the windows look weird.
+        // We use a bit of transparency so that if the user switches on the
+        // `transparent()` option they get immediate results.
+        egui::Color32::from_rgba_unmultiplied(12, 12, 12, 180).into()
+    }
+
+    /// Controls whether or not the native window position and size will be
+    /// persisted (only if the "persistence" feature is enabled).
+    fn persist_native_window(&self) -> bool {
+        true
+    }
+
+    /// Controls whether or not the egui memory (window positions etc) will be
+    /// persisted (only if the "persistence" feature is enabled).
+    fn persist_egui_memory(&self) -> bool {
+        true
+    }
+
+    /// If `true` a warm-up call to [`Self::update`] will be issued where
+    /// `ctx.memory().everything_is_visible()` will be set to `true`.
+    ///
+    /// This can help pre-caching resources loaded by different parts of the UI, preventing stutter later on.
+    ///
+    /// In this warm-up call, all painted shapes will be ignored.
+    ///
+    /// The default is `false`, and it is unlikely you will want to change this.
+    fn warm_up_enabled(&self) -> bool {
+        false
+    }
+}
+
+/// Options controlling the behavior of a native window.
+///
+/// Only a single native window is currently supported.
+#[derive(Clone)]
+pub struct NativeOptions {
+    /// Sets whether or not the window will always be on top of other windows.
+    pub always_on_top: bool,
+
+    /// Show window in maximized mode
+    pub maximized: bool,
+
+    /// On desktop: add window decorations (i.e. a frame around your app)?
+    /// If false it will be difficult to move and resize the app.
+    pub decorated: bool,
+
+    /// On Windows: enable drag and drop support. Drag and drop can
+    /// not be disabled on other platforms.
+    ///
+    /// See [winit's documentation][drag_and_drop] for information on why you
+    /// might want to disable this on windows.
+    ///
+    /// [drag_and_drop]: https://docs.rs/winit/latest/x86_64-pc-windows-msvc/winit/platform/windows/trait.WindowBuilderExtWindows.html#tymethod.with_drag_and_drop
+    pub drag_and_drop_support: bool,
+
+    /// The application icon, e.g. in the Windows task bar etc.
+    pub icon_data: Option<IconData>,
+
+    /// The initial (inner) position of the native window in points (logical pixels).
+    pub initial_window_pos: Option<egui::Pos2>,
+
+    /// The initial inner size of the native window in points (logical pixels).
+    pub initial_window_size: Option<egui::Vec2>,
+
+    /// The minimum inner window size
+    pub min_window_size: Option<egui::Vec2>,
+
+    /// The maximum inner window size
+    pub max_window_size: Option<egui::Vec2>,
+
+    /// Should the app window be resizable?
+    pub resizable: bool,
+
+    /// On desktop: make the window transparent.
+    /// You control the transparency with [`App::clear_color()`].
+    /// You should avoid having a [`egui::CentralPanel`], or make sure its frame is also transparent.
+    pub transparent: bool,
+
+    /// Turn on vertical syncing, limiting the FPS to the display refresh rate.
+    ///
+    /// The default is `true`.
+    pub vsync: bool,
+
+    /// Set the level of the multisampling anti-aliasing (MSAA).
+    ///
+    /// Must be a power-of-two. Higher = more smooth 3D.
+    ///
+    /// A value of `0` turns it off (default).
+    ///
+    /// `egui` already performs anti-aliasing via "feathering"
+    /// (controlled by [`egui::epaint::TessellationOptions`]),
+    /// but if you are embedding 3D in egui you may want to turn on multisampling.
+    pub multisampling: u16,
+
+    /// Sets the number of bits in the depth buffer.
+    ///
+    /// `egui` doesn't need the depth buffer, so the default value is 0.
+    pub depth_buffer: u8,
+
+    /// Sets the number of bits in the stencil buffer.
+    ///
+    /// `egui` doesn't need the stencil buffer, so the default value is 0.
+    pub stencil_buffer: u8,
+}
+
+impl Default for NativeOptions {
+    fn default() -> Self {
+        Self {
+            always_on_top: false,
+            maximized: false,
+            decorated: true,
+            drag_and_drop_support: true,
+            icon_data: None,
+            initial_window_pos: None,
+            initial_window_size: None,
+            min_window_size: None,
+            max_window_size: None,
+            resizable: true,
+            transparent: false,
+            vsync: true,
+            multisampling: 0,
+            depth_buffer: 0,
+            stencil_buffer: 0,
+        }
+    }
+}
+
+/// Image data for an application icon.
+#[derive(Clone)]
+pub struct IconData {
+    /// RGBA pixels, unmultiplied.
+    pub rgba: Vec<u8>,
+
+    /// Image width. This should be a multiple of 4.
+    pub width: u32,
+
+    /// Image height. This should be a multiple of 4.
+    pub height: u32,
+}
+
+/// Represents the surroundings of your app.
+///
+/// It provides methods to inspect the surroundings (are we on the web?),
+/// allocate textures, and change settings (e.g. window size).
+pub struct Frame {
+    /// Information about the integration.
+    #[doc(hidden)]
+    pub info: IntegrationInfo,
+
+    /// Where the app can issue commands back to the integration.
+    #[doc(hidden)]
+    pub output: backend::AppOutput,
+
+    /// A place where you can store custom data in a way that persists when you restart the app.
+    #[doc(hidden)]
+    pub storage: Option<Box<dyn Storage>>,
+
+    /// A reference to the underlying [`glow`] (OpenGL) context.
+    #[doc(hidden)]
+    pub gl: std::rc::Rc<glow::Context>,
+}
+
+impl Frame {
+    /// True if you are in a web environment.
+    pub fn is_web(&self) -> bool {
+        self.info.web_info.is_some()
+    }
+
+    /// Information about the integration.
+    pub fn info(&self) -> IntegrationInfo {
+        self.info.clone()
+    }
+
+    /// A place where you can store custom data in a way that persists when you restart the app.
+    pub fn storage(&self) -> Option<&dyn Storage> {
+        self.storage.as_deref()
+    }
+
+    /// A place where you can store custom data in a way that persists when you restart the app.
+    pub fn storage_mut(&mut self) -> Option<&mut (dyn Storage + 'static)> {
+        self.storage.as_deref_mut()
+    }
+
+    /// A reference to the underlying [`glow`] (OpenGL) context.
+    ///
+    /// This can be used, for instance, to:
+    /// * Render things to offscreen buffers.
+    /// * Read the pixel buffer from the previous frame (`glow::Context::read_pixels`).
+    /// * Render things behind the egui windows.
+    ///
+    /// Note that all egui painting is deferred to after the call to [`App::update`]
+    /// ([`egui`] only collects [`egui::Shape`]s and then eframe paints them all in one go later on).
+    pub fn gl(&self) -> &std::rc::Rc<glow::Context> {
+        &self.gl
+    }
+
+    /// Signal the app to stop/exit/quit the app (only works for native apps, not web apps).
+    /// The framework will not quit immediately, but at the end of the this frame.
+    pub fn quit(&mut self) {
+        self.output.quit = true;
+    }
+
+    /// Set the desired inner size of the window (in egui points).
+    pub fn set_window_size(&mut self, size: egui::Vec2) {
+        self.output.window_size = Some(size);
+    }
+
+    /// Set the desired title of the window.
+    pub fn set_window_title(&mut self, title: &str) {
+        self.output.window_title = Some(title.to_owned());
+    }
+
+    /// Set whether to show window decorations (i.e. a frame around you app).
+    /// If false it will be difficult to move and resize the app.
+    pub fn set_decorations(&mut self, decorated: bool) {
+        self.output.decorated = Some(decorated);
+    }
+
+    /// set the position of the outer window
+    pub fn set_window_pos(&mut self, pos: egui::Pos2) {
+        self.output.window_pos = Some(pos);
+    }
+
+    /// When called, the native window will follow the
+    /// movement of the cursor while the primary mouse button is down.
+    ///
+    /// Does not work on the web.
+    pub fn drag_window(&mut self) {
+        self.output.drag_window = true;
+    }
+
+    /// for integrations only: call once per frame
+    #[doc(hidden)]
+    pub fn take_app_output(&mut self) -> backend::AppOutput {
+        std::mem::take(&mut self.output)
+    }
+}
+
+/// Information about the web environment (if applicable).
+#[derive(Clone, Debug)]
+pub struct WebInfo {
+    /// Information about the URL.
+    pub location: Location,
+}
+
+/// Information about the URL.
+///
+/// Everything has been percent decoded (`%20` -> ` ` etc).
+#[derive(Clone, Debug)]
+pub struct Location {
+    /// The full URL (`location.href`) without the hash.
+    ///
+    /// Example: `"http://www.example.com:80/index.html?foo=bar"`.
+    pub url: String,
+
+    /// `location.protocol`
+    ///
+    /// Example: `"http:"`.
+    pub protocol: String,
+
+    /// `location.host`
+    ///
+    /// Example: `"example.com:80"`.
+    pub host: String,
+
+    /// `location.hostname`
+    ///
+    /// Example: `"example.com"`.
+    pub hostname: String,
+
+    /// `location.port`
+    ///
+    /// Example: `"80"`.
+    pub port: String,
+
+    /// The "#fragment" part of "www.example.com/index.html?query#fragment".
+    ///
+    /// Note that the leading `#` is included in the string.
+    /// Also known as "hash-link" or "anchor".
+    pub hash: String,
+
+    /// The "query" part of "www.example.com/index.html?query#fragment".
+    ///
+    /// Note that the leading `?` is NOT included in the string.
+    ///
+    /// Use [`Self::web_query_map]` to get the parsed version of it.
+    pub query: String,
+
+    /// The parsed "query" part of "www.example.com/index.html?query#fragment".
+    ///
+    /// "foo=42&bar%20" is parsed as `{"foo": "42",  "bar ": ""}`
+    pub query_map: std::collections::BTreeMap<String, String>,
+
+    /// `location.origin`
+    ///
+    /// Example: `"http://www.example.com:80"`.
+    pub origin: String,
+}
+
+/// Information about the integration passed to the use app each frame.
+#[derive(Clone, Debug)]
+pub struct IntegrationInfo {
+    /// If the app is running in a Web context, this returns information about the environment.
+    pub web_info: Option<WebInfo>,
+
+    /// Does the system prefer dark mode (over light mode)?
+    /// `None` means "don't know".
+    pub prefer_dark_mode: Option<bool>,
+
+    /// Seconds of cpu usage (in seconds) of UI code on the previous frame.
+    /// `None` if this is the first frame.
+    pub cpu_usage: Option<f32>,
+
+    /// The OS native pixels-per-point
+    pub native_pixels_per_point: Option<f32>,
+}
+
+// ----------------------------------------------------------------------------
+
+/// A place where you can store custom data in a way that persists when you restart the app.
+///
+/// On the web this is backed by [local storage](https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage).
+/// On desktop this is backed by the file system.
+///
+/// See [`CreationContext::storage`] and [`App::save`].
+pub trait Storage {
+    /// Get the value for the given key.
+    fn get_string(&self, key: &str) -> Option<String>;
+    /// Set the value for the given key.
+    fn set_string(&mut self, key: &str, value: String);
+
+    /// write-to-disk or similar
+    fn flush(&mut self);
+}
+
+/// Stores nothing.
+#[derive(Clone, Default)]
+pub(crate) struct DummyStorage {}
+
+impl Storage for DummyStorage {
+    fn get_string(&self, _key: &str) -> Option<String> {
+        None
+    }
+    fn set_string(&mut self, _key: &str, _value: String) {}
+    fn flush(&mut self) {}
+}
+
+/// Get and deserialize the [RON](https://github.com/ron-rs/ron) stored at the given key.
+#[cfg(feature = "ron")]
+pub fn get_value<T: serde::de::DeserializeOwned>(storage: &dyn Storage, key: &str) -> Option<T> {
+    storage
+        .get_string(key)
+        .and_then(|value| ron::from_str(&value).ok())
+}
+
+/// Serialize the given value as [RON](https://github.com/ron-rs/ron) and store with the given key.
+#[cfg(feature = "ron")]
+pub fn set_value<T: serde::Serialize>(storage: &mut dyn Storage, key: &str, value: &T) {
+    storage.set_string(key, ron::ser::to_string(value).unwrap());
+}
+
+/// [`Storage`] key used for app
+pub const APP_KEY: &str = "app";
+
+// ----------------------------------------------------------------------------
+
+/// You only need to look here if you are writing a backend for `epi`.
+#[doc(hidden)]
+pub mod backend {
+    /// Action that can be taken by the user app.
+    #[derive(Clone, Debug, Default)]
+    #[must_use]
+    pub struct AppOutput {
+        /// Set to `true` to stop the app.
+        /// This does nothing for web apps.
+        pub quit: bool,
+
+        /// Set to some size to resize the outer window (e.g. glium window) to this size.
+        pub window_size: Option<egui::Vec2>,
+
+        /// Set to some string to rename the outer window (e.g. glium window) to this title.
+        pub window_title: Option<String>,
+
+        /// Set to some bool to change window decorations.
+        pub decorated: Option<bool>,
+
+        /// Set to true to drag window while primary mouse button is down.
+        pub drag_window: bool,
+
+        /// Set to some position to move the outer window (e.g. glium window) to this position
+        pub window_pos: Option<egui::Pos2>,
+    }
+}

eframe/src/lib.rs

@@ -1,18 +1,14 @@
-//! eframe - the egui framework crate
+//! eframe - the [`egui`] framework crate
 //!
 //! If you are planning to write an app for web or native,
-//! and are happy with just using egui for all visuals,
-//! Then `eframe` is for you!
+//! and want to use [`egui`] for everything, then `eframe` is for you!
 //!
 //! To get started, see the [examples](https://github.com/emilk/egui/tree/master/examples).
 //! To learn how to set up `eframe` for web and native, go to <https://github.com/emilk/eframe_template/> and follow the instructions there!
 //!
-//! In short, you implement [`App`] and then
+//! In short, you implement [`App`] (especially [`App::update`]) and then
 //! call [`crate::run_native`] from your `main.rs`, and/or call `eframe::start_web` from your `lib.rs`.
 //!
-//! `eframe` is implemented using [`egui_web`](https://github.com/emilk/egui/tree/master/egui_web) for web and
-//! [`egui_glow`](https://github.com/emilk/egui/tree/master/egui_glow) for native.
-//!
 //! ## Usage, native:
 //! ``` no_run
 //! use eframe::egui;
@@ -60,7 +56,9 @@
 #![allow(clippy::needless_doctest_main)]
 
 // Re-export all useful libraries:
-pub use {egui, egui::emath, egui::epaint, epi};
+pub use {egui, egui::emath, egui::epaint, glow};
+
+mod epi;
 
 // Re-export everything in `epi` so `eframe` users don't have to care about what `epi` is:
 pub use epi::*;
@@ -69,7 +67,13 @@ pub use epi::*;
 // When compiling for web
 
 #[cfg(target_arch = "wasm32")]
-pub use egui_web::wasm_bindgen;
+mod web;
+
+#[cfg(target_arch = "wasm32")]
+pub use wasm_bindgen;
+
+#[cfg(target_arch = "wasm32")]
+pub use web_sys;
 
 /// Install event listeners to register different input events
 /// and start running the given app.
@@ -90,7 +94,7 @@ pub use egui_web::wasm_bindgen;
 /// ```
 #[cfg(target_arch = "wasm32")]
 pub fn start_web(canvas_id: &str, app_creator: AppCreator) -> Result<(), wasm_bindgen::JsValue> {
-    egui_web::start(canvas_id, app_creator)?;
+    web::start(canvas_id, app_creator)?;
     Ok(())
 }
 

eframe/src/native/epi_integration.rs

@@ -1,3 +1,4 @@
+use crate::epi;
 use egui_winit::{native_pixels_per_point, WindowSettings};
 
 pub fn points_to_size(points: egui::Vec2) -> winit::dpi::LogicalSize<f64> {
@@ -136,7 +137,7 @@ pub fn handle_app_output(
 /// For loading/saving app state and/or egui memory to disk.
 pub fn create_storage(_app_name: &str) -> Option<Box<dyn epi::Storage>> {
     #[cfg(feature = "persistence")]
-    if let Some(storage) = epi::file_storage::FileStorage::from_app_name(_app_name) {
+    if let Some(storage) = super::file_storage::FileStorage::from_app_name(_app_name) {
         return Some(Box::new(storage));
     }
     None
@@ -158,7 +159,6 @@ pub struct EpiIntegration {
 
 impl EpiIntegration {
     pub fn new(
-        integration_name: &'static str,
         gl: std::rc::Rc<glow::Context>,
         max_texture_side: usize,
         window: &winit::window::Window,
@@ -172,7 +172,6 @@ impl EpiIntegration {
 
         let frame = epi::Frame {
             info: epi::IntegrationInfo {
-                name: integration_name,
                 web_info: None,
                 prefer_dark_mode,
                 cpu_usage: None,

eframe/src/native/file_storage.rs

@@ -0,0 +1,116 @@
+use std::{
+    collections::HashMap,
+    path::{Path, PathBuf},
+};
+
+// ----------------------------------------------------------------------------
+
+/// A key-value store backed by a [RON](https://github.com/ron-rs/ron) file on disk.
+/// Used to restore egui state, glium window position/size and app state.
+pub struct FileStorage {
+    ron_filepath: PathBuf,
+    kv: HashMap<String, String>,
+    dirty: bool,
+    last_save_join_handle: Option<std::thread::JoinHandle<()>>,
+}
+
+impl Drop for FileStorage {
+    fn drop(&mut self) {
+        if let Some(join_handle) = self.last_save_join_handle.take() {
+            join_handle.join().ok();
+        }
+    }
+}
+
+impl FileStorage {
+    /// Store the state in this .ron file.
+    pub fn from_ron_filepath(ron_filepath: impl Into<PathBuf>) -> Self {
+        let ron_filepath: PathBuf = ron_filepath.into();
+        Self {
+            kv: read_ron(&ron_filepath).unwrap_or_default(),
+            ron_filepath,
+            dirty: false,
+            last_save_join_handle: None,
+        }
+    }
+
+    /// Find a good place to put the files that the OS likes.
+    pub fn from_app_name(app_name: &str) -> Option<Self> {
+        if let Some(proj_dirs) = directories_next::ProjectDirs::from("", "", app_name) {
+            let data_dir = proj_dirs.data_dir().to_path_buf();
+            if let Err(err) = std::fs::create_dir_all(&data_dir) {
+                tracing::warn!(
+                    "Saving disabled: Failed to create app path at {:?}: {}",
+                    data_dir,
+                    err
+                );
+                None
+            } else {
+                Some(Self::from_ron_filepath(data_dir.join("app.ron")))
+            }
+        } else {
+            tracing::warn!("Saving disabled: Failed to find path to data_dir.");
+            None
+        }
+    }
+}
+
+impl crate::Storage for FileStorage {
+    fn get_string(&self, key: &str) -> Option<String> {
+        self.kv.get(key).cloned()
+    }
+
+    fn set_string(&mut self, key: &str, value: String) {
+        if self.kv.get(key) != Some(&value) {
+            self.kv.insert(key.to_owned(), value);
+            self.dirty = true;
+        }
+    }
+
+    fn flush(&mut self) {
+        if self.dirty {
+            self.dirty = false;
+
+            let file_path = self.ron_filepath.clone();
+            let kv = self.kv.clone();
+
+            if let Some(join_handle) = self.last_save_join_handle.take() {
+                // wait for previous save to complete.
+                join_handle.join().ok();
+            }
+
+            let join_handle = std::thread::spawn(move || {
+                let file = std::fs::File::create(&file_path).unwrap();
+                let config = Default::default();
+                ron::ser::to_writer_pretty(file, &kv, config).unwrap();
+                tracing::trace!("Persisted to {:?}", file_path);
+            });
+
+            self.last_save_join_handle = Some(join_handle);
+        }
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+fn read_ron<T>(ron_path: impl AsRef<Path>) -> Option<T>
+where
+    T: serde::de::DeserializeOwned,
+{
+    match std::fs::File::open(ron_path) {
+        Ok(file) => {
+            let reader = std::io::BufReader::new(file);
+            match ron::de::from_reader(reader) {
+                Ok(value) => Some(value),
+                Err(err) => {
+                    tracing::warn!("Failed to parse RON: {}", err);
+                    None
+                }
+            }
+        }
+        Err(_err) => {
+            // File probably doesn't exist. That's fine.
+            None
+        }
+    }
+}

eframe/src/native/mod.rs

@@ -1,4 +1,8 @@
 mod epi_integration;
 mod run;
 
+/// File storage which can be used by native backends.
+#[cfg(feature = "persistence")]
+pub mod file_storage;
+
 pub use run::run;

eframe/src/native/run.rs

@@ -1,4 +1,5 @@
 use super::epi_integration;
+use crate::epi;
 use egui_winit::winit;
 
 struct RequestRepaintEvent;
@@ -50,7 +51,6 @@ pub fn run(app_name: &str, native_options: &epi::NativeOptions, app_creator: epi
         .unwrap_or_else(|error| panic!("some OpenGL error occurred {}\n", error));
 
     let mut integration = epi_integration::EpiIntegration::new(
-        "egui_glow",
         gl.clone(),
         painter.max_texture_side(),
         gl_window.window(),

eframe/src/web/backend.rs

@@ -0,0 +1,444 @@
+use super::{glow_wrapping::WrappedGlowPainter, *};
+
+use crate::epi;
+
+use egui::TexturesDelta;
+pub use egui::{pos2, Color32};
+
+// ----------------------------------------------------------------------------
+
+/// Data gathered between frames.
+#[derive(Default)]
+pub struct WebInput {
+    /// Required because we don't get a position on touched
+    pub latest_touch_pos: Option<egui::Pos2>,
+
+    /// Required to maintain a stable touch position for multi-touch gestures.
+    pub latest_touch_pos_id: Option<egui::TouchId>,
+
+    pub raw: egui::RawInput,
+}
+
+impl WebInput {
+    pub fn new_frame(&mut self, canvas_size: egui::Vec2) -> egui::RawInput {
+        egui::RawInput {
+            screen_rect: Some(egui::Rect::from_min_size(Default::default(), canvas_size)),
+            pixels_per_point: Some(native_pixels_per_point()), // We ALWAYS use the native pixels-per-point
+            time: Some(now_sec()),
+            ..self.raw.take()
+        }
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+use std::sync::atomic::Ordering::SeqCst;
+
+pub struct NeedRepaint(std::sync::atomic::AtomicBool);
+
+impl Default for NeedRepaint {
+    fn default() -> Self {
+        Self(true.into())
+    }
+}
+
+impl NeedRepaint {
+    pub fn fetch_and_clear(&self) -> bool {
+        self.0.swap(false, SeqCst)
+    }
+
+    pub fn set_true(&self) {
+        self.0.store(true, SeqCst);
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+fn web_location() -> epi::Location {
+    let location = web_sys::window().unwrap().location();
+
+    let hash = percent_decode(&location.hash().unwrap_or_default());
+
+    let query = location
+        .search()
+        .unwrap_or_default()
+        .strip_prefix('?')
+        .map(percent_decode)
+        .unwrap_or_default();
+
+    let query_map = parse_query_map(&query)
+        .iter()
+        .map(|(k, v)| ((*k).to_string(), (*v).to_string()))
+        .collect();
+
+    epi::Location {
+        url: percent_decode(&location.href().unwrap_or_default()),
+        protocol: percent_decode(&location.protocol().unwrap_or_default()),
+        host: percent_decode(&location.host().unwrap_or_default()),
+        hostname: percent_decode(&location.hostname().unwrap_or_default()),
+        port: percent_decode(&location.port().unwrap_or_default()),
+        hash,
+        query,
+        query_map,
+        origin: percent_decode(&location.origin().unwrap_or_default()),
+    }
+}
+
+fn parse_query_map(query: &str) -> BTreeMap<&str, &str> {
+    query
+        .split('&')
+        .filter_map(|pair| {
+            if pair.is_empty() {
+                None
+            } else {
+                Some(if let Some((key, value)) = pair.split_once('=') {
+                    (key, value)
+                } else {
+                    (pair, "")
+                })
+            }
+        })
+        .collect()
+}
+
+#[test]
+fn test_parse_query() {
+    assert_eq!(parse_query_map(""), BTreeMap::default());
+    assert_eq!(parse_query_map("foo"), BTreeMap::from_iter([("foo", "")]));
+    assert_eq!(
+        parse_query_map("foo=bar"),
+        BTreeMap::from_iter([("foo", "bar")])
+    );
+    assert_eq!(
+        parse_query_map("foo=bar&baz=42"),
+        BTreeMap::from_iter([("foo", "bar"), ("baz", "42")])
+    );
+    assert_eq!(
+        parse_query_map("foo&baz=42"),
+        BTreeMap::from_iter([("foo", ""), ("baz", "42")])
+    );
+    assert_eq!(
+        parse_query_map("foo&baz&&"),
+        BTreeMap::from_iter([("foo", ""), ("baz", "")])
+    );
+}
+
+// ----------------------------------------------------------------------------
+
+pub struct AppRunner {
+    pub(crate) frame: epi::Frame,
+    egui_ctx: egui::Context,
+    painter: WrappedGlowPainter,
+    pub(crate) input: WebInput,
+    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,
+    textures_delta: TexturesDelta,
+}
+
+impl AppRunner {
+    pub fn new(canvas_id: &str, app_creator: epi::AppCreator) -> Result<Self, JsValue> {
+        let painter = WrappedGlowPainter::new(canvas_id).map_err(JsValue::from)?;
+
+        let prefer_dark_mode = super::prefer_dark_mode();
+
+        let frame = epi::Frame {
+            info: epi::IntegrationInfo {
+                web_info: Some(epi::WebInfo {
+                    location: web_location(),
+                }),
+                prefer_dark_mode,
+                cpu_usage: None,
+                native_pixels_per_point: Some(native_pixels_per_point()),
+            },
+            output: Default::default(),
+            storage: Some(Box::new(LocalStorage::default())),
+            gl: painter.gl().clone(),
+        };
+
+        let needs_repaint: std::sync::Arc<NeedRepaint> = Default::default();
+
+        let egui_ctx = egui::Context::default();
+
+        {
+            let needs_repaint = needs_repaint.clone();
+            egui_ctx.set_request_repaint_callback(move || {
+                needs_repaint.0.store(true, SeqCst);
+            });
+        }
+
+        load_memory(&egui_ctx);
+        if prefer_dark_mode == Some(true) {
+            egui_ctx.set_visuals(egui::Visuals::dark());
+        } else {
+            egui_ctx.set_visuals(egui::Visuals::light());
+        }
+
+        let app = app_creator(&epi::CreationContext {
+            egui_ctx: egui_ctx.clone(),
+            integration_info: frame.info(),
+            storage: frame.storage(),
+            gl: painter.painter.gl().clone(),
+        });
+
+        let mut runner = Self {
+            frame,
+            egui_ctx,
+            painter,
+            input: Default::default(),
+            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(),
+        };
+
+        runner.input.raw.max_texture_side = Some(runner.painter.max_texture_side());
+
+        Ok(runner)
+    }
+
+    pub fn egui_ctx(&self) -> &egui::Context {
+        &self.egui_ctx
+    }
+
+    pub fn auto_save(&mut self) {
+        let now = now_sec();
+        let time_since_last_save = now - self.last_save_time;
+
+        if time_since_last_save > self.app.auto_save_interval().as_secs_f64() {
+            if self.app.persist_egui_memory() {
+                save_memory(&self.egui_ctx);
+            }
+            if let Some(storage) = self.frame.storage_mut() {
+                self.app.save(storage);
+            }
+            self.last_save_time = now;
+        }
+    }
+
+    pub fn canvas_id(&self) -> &str {
+        self.painter.canvas_id()
+    }
+
+    pub fn warm_up(&mut self) -> Result<(), JsValue> {
+        if self.app.warm_up_enabled() {
+            let saved_memory: egui::Memory = self.egui_ctx.memory().clone();
+            self.egui_ctx.memory().set_everything_is_visible(true);
+            self.logic()?;
+            *self.egui_ctx.memory() = saved_memory; // We don't want to remember that windows were huge.
+            self.egui_ctx.clear_animations();
+        }
+        Ok(())
+    }
+
+    /// Returns `true` if egui requests a repaint.
+    ///
+    /// Call [`Self::paint`] later to paint
+    pub fn logic(&mut self) -> Result<(bool, Vec<egui::ClippedPrimitive>), JsValue> {
+        let frame_start = now_sec();
+
+        resize_canvas_to_screen_size(self.canvas_id(), self.app.max_size_points());
+        let canvas_size = canvas_size_in_points(self.canvas_id());
+        let raw_input = self.input.new_frame(canvas_size);
+
+        let full_output = self.egui_ctx.run(raw_input, |egui_ctx| {
+            self.app.update(egui_ctx, &mut self.frame);
+        });
+        let egui::FullOutput {
+            platform_output,
+            needs_repaint,
+            textures_delta,
+            shapes,
+        } = full_output;
+
+        self.handle_platform_output(platform_output);
+        self.textures_delta.append(textures_delta);
+        let clipped_primitives = self.egui_ctx.tessellate(shapes);
+
+        {
+            let app_output = self.frame.take_app_output();
+            let epi::backend::AppOutput {
+                quit: _,         // Can't quit a web page
+                window_size: _,  // Can't resize a web page
+                window_title: _, // TODO: change title of window
+                decorated: _,    // Can't toggle decorations
+                drag_window: _,  // Can't be dragged
+                window_pos: _,   // Can't set position of a web page
+            } = app_output;
+        }
+
+        self.frame.info.cpu_usage = Some((now_sec() - frame_start) as f32);
+        Ok((needs_repaint, clipped_primitives))
+    }
+
+    pub fn clear_color_buffer(&self) {
+        self.painter.clear(self.app.clear_color());
+    }
+
+    /// Paint the results of the last call to [`Self::logic`].
+    pub fn paint(&mut self, clipped_primitives: &[egui::ClippedPrimitive]) -> Result<(), JsValue> {
+        let textures_delta = std::mem::take(&mut self.textures_delta);
+
+        self.painter.paint_and_update_textures(
+            clipped_primitives,
+            self.egui_ctx.pixels_per_point(),
+            &textures_delta,
+        )?;
+
+        Ok(())
+    }
+
+    fn handle_platform_output(&mut self, platform_output: egui::PlatformOutput) {
+        if self.egui_ctx.options().screen_reader {
+            self.screen_reader
+                .speak(&platform_output.events_description());
+        }
+
+        let egui::PlatformOutput {
+            cursor_icon,
+            open_url,
+            copied_text,
+            events: _, // already handled
+            mutable_text_under_cursor,
+            text_cursor_pos,
+        } = platform_output;
+
+        set_cursor_icon(cursor_icon);
+        if let Some(open) = open_url {
+            super::open_url(&open.url, open.new_tab);
+        }
+
+        #[cfg(web_sys_unstable_apis)]
+        if !copied_text.is_empty() {
+            set_clipboard_text(&copied_text);
+        }
+
+        #[cfg(not(web_sys_unstable_apis))]
+        let _ = copied_text;
+
+        self.mutable_text_under_cursor = mutable_text_under_cursor;
+
+        if self.text_cursor_pos != text_cursor_pos {
+            text_agent::move_text_cursor(text_cursor_pos, self.canvas_id());
+            self.text_cursor_pos = text_cursor_pos;
+        }
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+pub type AppRunnerRef = Arc<Mutex<AppRunner>>;
+
+pub struct AppRunnerContainer {
+    pub runner: AppRunnerRef,
+    /// Set to `true` if there is a panic.
+    /// Used to ignore callbacks after a panic.
+    pub panicked: Arc<AtomicBool>,
+}
+
+impl AppRunnerContainer {
+    /// Convenience function to reduce boilerplate and ensure that all event handlers
+    /// are dealt with in the same way
+    pub fn add_event_listener<E: wasm_bindgen::JsCast>(
+        &self,
+        target: &EventTarget,
+        event_name: &'static str,
+        mut closure: impl FnMut(E, MutexGuard<'_, AppRunner>) + 'static,
+    ) -> Result<(), JsValue> {
+        use wasm_bindgen::JsCast;
+
+        // Create a JS closure based on the FnMut provided
+        let closure = Closure::wrap({
+            // Clone atomics
+            let runner_ref = self.runner.clone();
+            let panicked = self.panicked.clone();
+
+            Box::new(move |event: web_sys::Event| {
+                // Only call the wrapped closure if the egui code has not panicked
+                if !panicked.load(Ordering::SeqCst) {
+                    // Cast the event to the expected event type
+                    let event = event.unchecked_into::<E>();
+
+                    closure(event, runner_ref.lock());
+                }
+            }) as Box<dyn FnMut(_)>
+        });
+
+        // Add the event listener to the target
+        target.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
+
+        // Bypass closure drop so that event handler can call the closure
+        closure.forget();
+
+        Ok(())
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+/// Install event listeners to register different input events
+/// and start running the given app.
+pub fn start(canvas_id: &str, app_creator: epi::AppCreator) -> Result<AppRunnerRef, JsValue> {
+    let mut runner = AppRunner::new(canvas_id, app_creator)?;
+    runner.warm_up()?;
+    start_runner(runner)
+}
+
+/// Install event listeners to register different input events
+/// and starts running the given [`AppRunner`].
+fn start_runner(app_runner: AppRunner) -> Result<AppRunnerRef, JsValue> {
+    let runner_container = AppRunnerContainer {
+        runner: Arc::new(Mutex::new(app_runner)),
+        panicked: Arc::new(AtomicBool::new(false)),
+    };
+
+    super::events::install_canvas_events(&runner_container)?;
+    super::events::install_document_events(&runner_container)?;
+    text_agent::install_text_agent(&runner_container)?;
+    super::events::repaint_every_ms(&runner_container, 1000)?; // just in case. TODO: make it a parameter
+
+    super::events::paint_and_schedule(&runner_container.runner, runner_container.panicked.clone())?;
+
+    // Disable all event handlers on panic
+    std::panic::set_hook(Box::new({
+        let previous_hook = std::panic::take_hook();
+
+        let panicked = runner_container.panicked;
+
+        move |panic_info| {
+            tracing::info_span!("egui_panic_handler").in_scope(|| {
+                tracing::trace!("setting panicked flag");
+
+                panicked.store(true, SeqCst);
+
+                tracing::info!("egui disabled all event handlers due to panic");
+            });
+
+            // Propagate panic info to the previously registered panic hook
+            previous_hook(panic_info);
+        }
+    }));
+
+    Ok(runner_container.runner)
+}
+
+// ----------------------------------------------------------------------------
+
+#[derive(Default)]
+struct LocalStorage {}
+
+impl epi::Storage for LocalStorage {
+    fn get_string(&self, key: &str) -> Option<String> {
+        local_storage_get(key)
+    }
+    fn set_string(&mut self, key: &str, value: String) {
+        local_storage_set(key, &value);
+    }
+    fn flush(&mut self) {}
+}

eframe/src/web/events.rs

@@ -0,0 +1,544 @@
+use super::*;
+use std::sync::atomic::{AtomicBool, Ordering};
+
+pub fn paint_and_schedule(
+    runner_ref: &AppRunnerRef,
+    panicked: Arc<AtomicBool>,
+) -> Result<(), JsValue> {
+    fn paint_if_needed(runner_ref: &AppRunnerRef) -> Result<(), JsValue> {
+        let mut runner_lock = runner_ref.lock();
+        if runner_lock.needs_repaint.fetch_and_clear() {
+            runner_lock.clear_color_buffer();
+            let (needs_repaint, clipped_primitives) = runner_lock.logic()?;
+            runner_lock.paint(&clipped_primitives)?;
+            if needs_repaint {
+                runner_lock.needs_repaint.set_true();
+            }
+            runner_lock.auto_save();
+        }
+
+        Ok(())
+    }
+
+    fn request_animation_frame(
+        runner_ref: AppRunnerRef,
+        panicked: Arc<AtomicBool>,
+    ) -> Result<(), JsValue> {
+        use wasm_bindgen::JsCast;
+        let window = web_sys::window().unwrap();
+        let closure = Closure::once(move || paint_and_schedule(&runner_ref, panicked));
+        window.request_animation_frame(closure.as_ref().unchecked_ref())?;
+        closure.forget(); // We must forget it, or else the callback is canceled on drop
+        Ok(())
+    }
+
+    // Only paint and schedule if there has been no panic
+    if !panicked.load(Ordering::SeqCst) {
+        paint_if_needed(runner_ref)?;
+        request_animation_frame(runner_ref.clone(), panicked)?;
+    }
+
+    Ok(())
+}
+
+pub fn install_document_events(runner_container: &AppRunnerContainer) -> Result<(), JsValue> {
+    let window = web_sys::window().unwrap();
+    let document = window.document().unwrap();
+
+    runner_container.add_event_listener(
+        &document,
+        "keydown",
+        |event: web_sys::KeyboardEvent, mut runner_lock| {
+            if event.is_composing() || event.key_code() == 229 {
+                // https://www.fxsitecompat.dev/en-CA/docs/2018/keydown-and-keyup-events-are-now-fired-during-ime-composition/
+                return;
+            }
+
+            let modifiers = modifiers_from_event(&event);
+            runner_lock.input.raw.modifiers = modifiers;
+
+            let key = event.key();
+
+            if let Some(key) = translate_key(&key) {
+                runner_lock.input.raw.events.push(egui::Event::Key {
+                    key,
+                    pressed: true,
+                    modifiers,
+                });
+            }
+            if !modifiers.ctrl
+                && !modifiers.command
+                && !should_ignore_key(&key)
+                // When text agent is shown, it sends text event instead.
+                && text_agent::text_agent().hidden()
+            {
+                runner_lock.input.raw.events.push(egui::Event::Text(key));
+            }
+            runner_lock.needs_repaint.set_true();
+
+            let egui_wants_keyboard = runner_lock.egui_ctx().wants_keyboard_input();
+
+            let prevent_default = if matches!(event.key().as_str(), "Tab") {
+                // Always prevent moving cursor to url bar.
+                // egui wants to use tab to move to the next text field.
+                true
+            } else if egui_wants_keyboard {
+                matches!(
+                    event.key().as_str(),
+                    "Backspace" // so we don't go back to previous page when deleting text
+                    | "ArrowDown" | "ArrowLeft" | "ArrowRight" | "ArrowUp" // cmd-left is "back" on Mac (https://github.com/emilk/egui/issues/58)
+                )
+            } else {
+                // We never want to prevent:
+                // * F5 / cmd-R (refresh)
+                // * cmd-shift-C (debug tools)
+                // * cmd/ctrl-c/v/x (or we stop copy/past/cut events)
+                false
+            };
+
+            // tracing::debug!(
+            //     "On key-down {:?}, egui_wants_keyboard: {}, prevent_default: {}",
+            //     event.key().as_str(),
+            //     egui_wants_keyboard,
+            //     prevent_default
+            // );
+
+            if prevent_default {
+                event.prevent_default();
+            }
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &document,
+        "keyup",
+        |event: web_sys::KeyboardEvent, mut runner_lock| {
+            let modifiers = modifiers_from_event(&event);
+            runner_lock.input.raw.modifiers = modifiers;
+            if let Some(key) = translate_key(&event.key()) {
+                runner_lock.input.raw.events.push(egui::Event::Key {
+                    key,
+                    pressed: false,
+                    modifiers,
+                });
+            }
+            runner_lock.needs_repaint.set_true();
+        },
+    )?;
+
+    #[cfg(web_sys_unstable_apis)]
+    runner_container.add_event_listener(
+        &document,
+        "paste",
+        |event: web_sys::ClipboardEvent, mut runner_lock| {
+            if let Some(data) = event.clipboard_data() {
+                if let Ok(text) = data.get_data("text") {
+                    let text = text.replace("\r\n", "\n");
+                    if !text.is_empty() {
+                        runner_lock.input.raw.events.push(egui::Event::Paste(text));
+                        runner_lock.needs_repaint.set_true();
+                    }
+                    event.stop_propagation();
+                    event.prevent_default();
+                }
+            }
+        },
+    )?;
+
+    #[cfg(web_sys_unstable_apis)]
+    runner_container.add_event_listener(
+        &document,
+        "cut",
+        |_: web_sys::ClipboardEvent, mut runner_lock| {
+            runner_lock.input.raw.events.push(egui::Event::Cut);
+            runner_lock.needs_repaint.set_true();
+        },
+    )?;
+
+    #[cfg(web_sys_unstable_apis)]
+    runner_container.add_event_listener(
+        &document,
+        "copy",
+        |_: web_sys::ClipboardEvent, mut runner_lock| {
+            runner_lock.input.raw.events.push(egui::Event::Copy);
+            runner_lock.needs_repaint.set_true();
+        },
+    )?;
+
+    for event_name in &["load", "pagehide", "pageshow", "resize"] {
+        runner_container.add_event_listener(
+            &window,
+            event_name,
+            |_: web_sys::Event, runner_lock| {
+                runner_lock.needs_repaint.set_true();
+            },
+        )?;
+    }
+
+    runner_container.add_event_listener(
+        &window,
+        "hashchange",
+        |_: web_sys::Event, mut runner_lock| {
+            // `epi::Frame::info(&self)` clones `epi::IntegrationInfo`, but we need to modify the original here
+            if let Some(web_info) = &mut runner_lock.frame.info.web_info {
+                web_info.location.hash = location_hash();
+            }
+        },
+    )?;
+
+    Ok(())
+}
+
+/// Repaint at least every `ms` milliseconds.
+pub fn repaint_every_ms(
+    runner_container: &AppRunnerContainer,
+    milliseconds: i32,
+) -> Result<(), JsValue> {
+    assert!(milliseconds >= 0);
+
+    use wasm_bindgen::JsCast;
+
+    let window = web_sys::window().unwrap();
+
+    let closure = Closure::wrap(Box::new({
+        let runner = runner_container.runner.clone();
+        let panicked = runner_container.panicked.clone();
+
+        move || {
+            // Do not lock the runner if the code has panicked
+            if !panicked.load(Ordering::SeqCst) {
+                runner.lock().needs_repaint.set_true();
+            }
+        }
+    }) as Box<dyn FnMut()>);
+
+    window.set_interval_with_callback_and_timeout_and_arguments_0(
+        closure.as_ref().unchecked_ref(),
+        milliseconds,
+    )?;
+
+    closure.forget();
+    Ok(())
+}
+
+pub fn install_canvas_events(runner_container: &AppRunnerContainer) -> Result<(), JsValue> {
+    use wasm_bindgen::JsCast;
+    let canvas = canvas_element(runner_container.runner.lock().canvas_id()).unwrap();
+
+    {
+        // By default, right-clicks open a context menu.
+        // We don't want to do that (right clicks is handled by egui):
+        let event_name = "contextmenu";
+        let closure = Closure::wrap(Box::new(move |event: web_sys::MouseEvent| {
+            event.prevent_default();
+        }) as Box<dyn FnMut(_)>);
+        canvas.add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())?;
+        closure.forget();
+    }
+
+    runner_container.add_event_listener(
+        &canvas,
+        "mousedown",
+        |event: web_sys::MouseEvent, mut runner_lock| {
+            if let Some(button) = button_from_mouse_event(&event) {
+                let pos = pos_from_mouse_event(runner_lock.canvas_id(), &event);
+                let modifiers = runner_lock.input.raw.modifiers;
+                runner_lock
+                    .input
+                    .raw
+                    .events
+                    .push(egui::Event::PointerButton {
+                        pos,
+                        button,
+                        pressed: true,
+                        modifiers,
+                    });
+                runner_lock.needs_repaint.set_true();
+            }
+            event.stop_propagation();
+            // Note: prevent_default breaks VSCode tab focusing, hence why we don't call it here.
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "mousemove",
+        |event: web_sys::MouseEvent, mut runner_lock| {
+            let pos = pos_from_mouse_event(runner_lock.canvas_id(), &event);
+            runner_lock
+                .input
+                .raw
+                .events
+                .push(egui::Event::PointerMoved(pos));
+            runner_lock.needs_repaint.set_true();
+            event.stop_propagation();
+            event.prevent_default();
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "mouseup",
+        |event: web_sys::MouseEvent, mut runner_lock| {
+            if let Some(button) = button_from_mouse_event(&event) {
+                let pos = pos_from_mouse_event(runner_lock.canvas_id(), &event);
+                let modifiers = runner_lock.input.raw.modifiers;
+                runner_lock
+                    .input
+                    .raw
+                    .events
+                    .push(egui::Event::PointerButton {
+                        pos,
+                        button,
+                        pressed: false,
+                        modifiers,
+                    });
+                runner_lock.needs_repaint.set_true();
+
+                text_agent::update_text_agent(runner_lock);
+            }
+            event.stop_propagation();
+            event.prevent_default();
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "mouseleave",
+        |event: web_sys::MouseEvent, mut runner_lock| {
+            runner_lock.input.raw.events.push(egui::Event::PointerGone);
+            runner_lock.needs_repaint.set_true();
+            event.stop_propagation();
+            event.prevent_default();
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "touchstart",
+        |event: web_sys::TouchEvent, mut runner_lock| {
+            let mut latest_touch_pos_id = runner_lock.input.latest_touch_pos_id;
+            let pos =
+                pos_from_touch_event(runner_lock.canvas_id(), &event, &mut latest_touch_pos_id);
+            runner_lock.input.latest_touch_pos_id = latest_touch_pos_id;
+            runner_lock.input.latest_touch_pos = Some(pos);
+            let modifiers = runner_lock.input.raw.modifiers;
+            runner_lock
+                .input
+                .raw
+                .events
+                .push(egui::Event::PointerButton {
+                    pos,
+                    button: egui::PointerButton::Primary,
+                    pressed: true,
+                    modifiers,
+                });
+
+            push_touches(&mut *runner_lock, egui::TouchPhase::Start, &event);
+            runner_lock.needs_repaint.set_true();
+            event.stop_propagation();
+            event.prevent_default();
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "touchmove",
+        |event: web_sys::TouchEvent, mut runner_lock| {
+            let mut latest_touch_pos_id = runner_lock.input.latest_touch_pos_id;
+            let pos =
+                pos_from_touch_event(runner_lock.canvas_id(), &event, &mut latest_touch_pos_id);
+            runner_lock.input.latest_touch_pos_id = latest_touch_pos_id;
+            runner_lock.input.latest_touch_pos = Some(pos);
+            runner_lock
+                .input
+                .raw
+                .events
+                .push(egui::Event::PointerMoved(pos));
+
+            push_touches(&mut *runner_lock, egui::TouchPhase::Move, &event);
+            runner_lock.needs_repaint.set_true();
+            event.stop_propagation();
+            event.prevent_default();
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "touchend",
+        |event: web_sys::TouchEvent, mut runner_lock| {
+            if let Some(pos) = runner_lock.input.latest_touch_pos {
+                let modifiers = runner_lock.input.raw.modifiers;
+                // First release mouse to click:
+                runner_lock
+                    .input
+                    .raw
+                    .events
+                    .push(egui::Event::PointerButton {
+                        pos,
+                        button: egui::PointerButton::Primary,
+                        pressed: false,
+                        modifiers,
+                    });
+                // Then remove hover effect:
+                runner_lock.input.raw.events.push(egui::Event::PointerGone);
+
+                push_touches(&mut *runner_lock, egui::TouchPhase::End, &event);
+                runner_lock.needs_repaint.set_true();
+                event.stop_propagation();
+                event.prevent_default();
+            }
+
+            // Finally, focus or blur text agent to toggle mobile keyboard:
+            text_agent::update_text_agent(runner_lock);
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "touchcancel",
+        |event: web_sys::TouchEvent, mut runner_lock| {
+            push_touches(&mut runner_lock, egui::TouchPhase::Cancel, &event);
+            event.stop_propagation();
+            event.prevent_default();
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "wheel",
+        |event: web_sys::WheelEvent, mut runner_lock| {
+            let scroll_multiplier = match event.delta_mode() {
+                web_sys::WheelEvent::DOM_DELTA_PAGE => {
+                    canvas_size_in_points(runner_lock.canvas_id()).y
+                }
+                web_sys::WheelEvent::DOM_DELTA_LINE => {
+                    #[allow(clippy::let_and_return)]
+                    let points_per_scroll_line = 8.0; // Note that this is intentionally different from what we use in egui_glium / winit.
+                    points_per_scroll_line
+                }
+                _ => 1.0, // DOM_DELTA_PIXEL
+            };
+
+            let mut delta =
+                -scroll_multiplier * egui::vec2(event.delta_x() as f32, event.delta_y() as f32);
+
+            // Report a zoom event in case CTRL (on Windows or Linux) or CMD (on Mac) is pressed.
+            // This if-statement is equivalent to how `Modifiers.command` is determined in
+            // `modifiers_from_event()`, but we cannot directly use that fn for a [`WheelEvent`].
+            if event.ctrl_key() || event.meta_key() {
+                let factor = (delta.y / 200.0).exp();
+                runner_lock.input.raw.events.push(egui::Event::Zoom(factor));
+            } else {
+                if event.shift_key() {
+                    // Treat as horizontal scrolling.
+                    // Note: one Mac we already get horizontal scroll events when shift is down.
+                    delta = egui::vec2(delta.x + delta.y, 0.0);
+                }
+
+                runner_lock
+                    .input
+                    .raw
+                    .events
+                    .push(egui::Event::Scroll(delta));
+            }
+
+            runner_lock.needs_repaint.set_true();
+            event.stop_propagation();
+            event.prevent_default();
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "dragover",
+        |event: web_sys::DragEvent, mut runner_lock| {
+            if let Some(data_transfer) = event.data_transfer() {
+                runner_lock.input.raw.hovered_files.clear();
+                for i in 0..data_transfer.items().length() {
+                    if let Some(item) = data_transfer.items().get(i) {
+                        runner_lock.input.raw.hovered_files.push(egui::HoveredFile {
+                            mime: item.type_(),
+                            ..Default::default()
+                        });
+                    }
+                }
+                runner_lock.needs_repaint.set_true();
+                event.stop_propagation();
+                event.prevent_default();
+            }
+        },
+    )?;
+
+    runner_container.add_event_listener(
+        &canvas,
+        "dragleave",
+        |event: web_sys::DragEvent, mut runner_lock| {
+            runner_lock.input.raw.hovered_files.clear();
+            runner_lock.needs_repaint.set_true();
+            event.stop_propagation();
+            event.prevent_default();
+        },
+    )?;
+
+    runner_container.add_event_listener(&canvas, "drop", {
+        let runner_ref = runner_container.runner.clone();
+
+        move |event: web_sys::DragEvent, mut runner_lock| {
+            if let Some(data_transfer) = event.data_transfer() {
+                runner_lock.input.raw.hovered_files.clear();
+                runner_lock.needs_repaint.set_true();
+                // Unlock the runner so it can be locked after a future await point
+                drop(runner_lock);
+
+                if let Some(files) = data_transfer.files() {
+                    for i in 0..files.length() {
+                        if let Some(file) = files.get(i) {
+                            let name = file.name();
+                            let last_modified = std::time::UNIX_EPOCH
+                                + std::time::Duration::from_millis(file.last_modified() as u64);
+
+                            tracing::debug!("Loading {:?} ({} bytes)…", name, file.size());
+
+                            let future = wasm_bindgen_futures::JsFuture::from(file.array_buffer());
+
+                            let runner_ref = runner_ref.clone();
+                            let future = async move {
+                                match future.await {
+                                    Ok(array_buffer) => {
+                                        let bytes = js_sys::Uint8Array::new(&array_buffer).to_vec();
+                                        tracing::debug!(
+                                            "Loaded {:?} ({} bytes).",
+                                            name,
+                                            bytes.len()
+                                        );
+
+                                        // Re-lock the mutex on the other side of the await point
+                                        let mut runner_lock = runner_ref.lock();
+                                        runner_lock.input.raw.dropped_files.push(
+                                            egui::DroppedFile {
+                                                name,
+                                                last_modified: Some(last_modified),
+                                                bytes: Some(bytes.into()),
+                                                ..Default::default()
+                                            },
+                                        );
+                                        runner_lock.needs_repaint.set_true();
+                                    }
+                                    Err(err) => {
+                                        tracing::error!("Failed to read file: {:?}", err);
+                                    }
+                                }
+                            };
+                            wasm_bindgen_futures::spawn_local(future);
+                        }
+                    }
+                }
+                event.stop_propagation();
+                event.prevent_default();
+            }
+        }
+    })?;
+
+    Ok(())
+}

eframe/src/web/glow_wrapping.rs

@@ -0,0 +1,158 @@
+use egui::{ClippedPrimitive, Rgba};
+use egui_glow::glow;
+use wasm_bindgen::JsCast;
+use wasm_bindgen::JsValue;
+use web_sys::HtmlCanvasElement;
+#[cfg(not(target_arch = "wasm32"))]
+use web_sys::{WebGl2RenderingContext, WebGlRenderingContext};
+
+pub(crate) struct WrappedGlowPainter {
+    pub(crate) canvas: HtmlCanvasElement,
+    pub(crate) canvas_id: String,
+    pub(crate) painter: egui_glow::Painter,
+}
+
+impl WrappedGlowPainter {
+    pub fn new(canvas_id: &str) -> Result<Self, String> {
+        let canvas = super::canvas_element_or_die(canvas_id);
+
+        let (gl, shader_prefix) = init_glow_context_from_canvas(&canvas)?;
+        let gl = std::rc::Rc::new(gl);
+
+        let dimension = [canvas.width() as i32, canvas.height() as i32];
+        let painter = egui_glow::Painter::new(gl, Some(dimension), shader_prefix)
+            .map_err(|error| format!("Error starting glow painter: {}", error))?;
+
+        Ok(Self {
+            canvas,
+            canvas_id: canvas_id.to_owned(),
+            painter,
+        })
+    }
+}
+
+impl WrappedGlowPainter {
+    pub fn gl(&self) -> &std::rc::Rc<glow::Context> {
+        self.painter.gl()
+    }
+
+    pub fn max_texture_side(&self) -> usize {
+        self.painter.max_texture_side()
+    }
+
+    pub fn canvas_id(&self) -> &str {
+        &self.canvas_id
+    }
+
+    pub fn set_texture(&mut self, tex_id: egui::TextureId, delta: &egui::epaint::ImageDelta) {
+        self.painter.set_texture(tex_id, delta);
+    }
+
+    pub fn free_texture(&mut self, tex_id: egui::TextureId) {
+        self.painter.free_texture(tex_id);
+    }
+
+    pub fn clear(&self, clear_color: Rgba) {
+        let canvas_dimension = [self.canvas.width(), self.canvas.height()];
+        egui_glow::painter::clear(self.painter.gl(), canvas_dimension, clear_color);
+    }
+
+    pub fn paint_primitives(
+        &mut self,
+        clipped_primitives: &[ClippedPrimitive],
+        pixels_per_point: f32,
+    ) -> Result<(), JsValue> {
+        let canvas_dimension = [self.canvas.width(), self.canvas.height()];
+        self.painter
+            .paint_primitives(canvas_dimension, pixels_per_point, clipped_primitives);
+        Ok(())
+    }
+
+    pub fn paint_and_update_textures(
+        &mut self,
+        clipped_primitives: &[egui::ClippedPrimitive],
+        pixels_per_point: f32,
+        textures_delta: &egui::TexturesDelta,
+    ) -> Result<(), JsValue> {
+        for (id, image_delta) in &textures_delta.set {
+            self.set_texture(*id, image_delta);
+        }
+
+        self.paint_primitives(clipped_primitives, pixels_per_point)?;
+
+        for &id in &textures_delta.free {
+            self.free_texture(id);
+        }
+
+        Ok(())
+    }
+}
+
+/// Returns glow context and shader prefix.
+fn init_glow_context_from_canvas(
+    canvas: &HtmlCanvasElement,
+) -> Result<(glow::Context, &'static str), String> {
+    const BEST_FIRST: bool = true;
+
+    let result = if BEST_FIRST {
+        // Trying WebGl2 first
+        init_webgl2(canvas).or_else(|| init_webgl1(canvas))
+    } else {
+        // Trying WebGl1 first (useful for testing).
+        tracing::warn!("Looking for WebGL1 first");
+        init_webgl1(canvas).or_else(|| init_webgl2(canvas))
+    };
+
+    if let Some(result) = result {
+        Ok(result)
+    } else {
+        Err("WebGL isn't supported".into())
+    }
+}
+
+fn init_webgl1(canvas: &HtmlCanvasElement) -> Option<(glow::Context, &'static str)> {
+    let gl1_ctx = canvas
+        .get_context("webgl")
+        .expect("Failed to query about WebGL2 context");
+
+    let gl1_ctx = gl1_ctx?;
+    tracing::debug!("WebGL1 selected.");
+
+    let gl1_ctx = gl1_ctx
+        .dyn_into::<web_sys::WebGlRenderingContext>()
+        .unwrap();
+
+    let shader_prefix = if super::webgl1_requires_brightening(&gl1_ctx) {
+        tracing::debug!("Enabling webkitGTK brightening workaround.");
+        "#define APPLY_BRIGHTENING_GAMMA"
+    } else {
+        ""
+    };
+
+    let gl = glow::Context::from_webgl1_context(gl1_ctx);
+
+    Some((gl, shader_prefix))
+}
+
+fn init_webgl2(canvas: &HtmlCanvasElement) -> Option<(glow::Context, &'static str)> {
+    let gl2_ctx = canvas
+        .get_context("webgl2")
+        .expect("Failed to query about WebGL2 context");
+
+    let gl2_ctx = gl2_ctx?;
+    tracing::debug!("WebGL2 selected.");
+
+    let gl2_ctx = gl2_ctx
+        .dyn_into::<web_sys::WebGl2RenderingContext>()
+        .unwrap();
+    let gl = glow::Context::from_webgl2_context(gl2_ctx);
+    let shader_prefix = "";
+
+    Some((gl, shader_prefix))
+}
+
+trait DummyWebGLConstructor {
+    fn from_webgl1_context(context: web_sys::WebGlRenderingContext) -> Self;
+
+    fn from_webgl2_context(context: web_sys::WebGl2RenderingContext) -> Self;
+}

eframe/src/web/input.rs

@@ -0,0 +1,189 @@
+use super::{canvas_element, canvas_origin, AppRunner};
+
+pub fn pos_from_mouse_event(canvas_id: &str, event: &web_sys::MouseEvent) -> egui::Pos2 {
+    let canvas = canvas_element(canvas_id).unwrap();
+    let rect = canvas.get_bounding_client_rect();
+    egui::Pos2 {
+        x: event.client_x() as f32 - rect.left() as f32,
+        y: event.client_y() as f32 - rect.top() as f32,
+    }
+}
+
+pub fn button_from_mouse_event(event: &web_sys::MouseEvent) -> Option<egui::PointerButton> {
+    match event.button() {
+        0 => Some(egui::PointerButton::Primary),
+        1 => Some(egui::PointerButton::Middle),
+        2 => Some(egui::PointerButton::Secondary),
+        _ => None,
+    }
+}
+
+/// A single touch is translated to a pointer movement. When a second touch is added, the pointer
+/// should not jump to a different position. Therefore, we do not calculate the average position
+/// of all touches, but we keep using the same touch as long as it is available.
+///
+/// `touch_id_for_pos` is the [`TouchId`](egui::TouchId) of the [`Touch`](web_sys::Touch) we previously used to determine the
+/// pointer position.
+pub fn pos_from_touch_event(
+    canvas_id: &str,
+    event: &web_sys::TouchEvent,
+    touch_id_for_pos: &mut Option<egui::TouchId>,
+) -> egui::Pos2 {
+    let touch_for_pos = if let Some(touch_id_for_pos) = touch_id_for_pos {
+        // search for the touch we previously used for the position
+        // (unfortunately, `event.touches()` is not a rust collection):
+        (0..event.touches().length())
+            .into_iter()
+            .map(|i| event.touches().get(i).unwrap())
+            .find(|touch| egui::TouchId::from(touch.identifier()) == *touch_id_for_pos)
+    } else {
+        None
+    };
+    // Use the touch found above or pick the first, or return a default position if there is no
+    // touch at all. (The latter is not expected as the current method is only called when there is
+    // at least one touch.)
+    touch_for_pos
+        .or_else(|| event.touches().get(0))
+        .map_or(Default::default(), |touch| {
+            *touch_id_for_pos = Some(egui::TouchId::from(touch.identifier()));
+            pos_from_touch(canvas_origin(canvas_id), &touch)
+        })
+}
+
+fn pos_from_touch(canvas_origin: egui::Pos2, touch: &web_sys::Touch) -> egui::Pos2 {
+    egui::Pos2 {
+        x: touch.page_x() as f32 - canvas_origin.x as f32,
+        y: touch.page_y() as f32 - canvas_origin.y as f32,
+    }
+}
+
+pub fn push_touches(runner: &mut AppRunner, phase: egui::TouchPhase, event: &web_sys::TouchEvent) {
+    let canvas_origin = canvas_origin(runner.canvas_id());
+    for touch_idx in 0..event.changed_touches().length() {
+        if let Some(touch) = event.changed_touches().item(touch_idx) {
+            runner.input.raw.events.push(egui::Event::Touch {
+                device_id: egui::TouchDeviceId(0),
+                id: egui::TouchId::from(touch.identifier()),
+                phase,
+                pos: pos_from_touch(canvas_origin, &touch),
+                force: touch.force(),
+            });
+        }
+    }
+}
+
+/// Web sends all keys as strings, so it is up to us to figure out if it is
+/// a real text input or the name of a key.
+pub fn should_ignore_key(key: &str) -> bool {
+    let is_function_key = key.starts_with('F') && key.len() > 1;
+    is_function_key
+        || matches!(
+            key,
+            "Alt"
+                | "ArrowDown"
+                | "ArrowLeft"
+                | "ArrowRight"
+                | "ArrowUp"
+                | "Backspace"
+                | "CapsLock"
+                | "ContextMenu"
+                | "Control"
+                | "Delete"
+                | "End"
+                | "Enter"
+                | "Esc"
+                | "Escape"
+                | "GroupNext" // https://github.com/emilk/egui/issues/510
+                | "Help"
+                | "Home"
+                | "Insert"
+                | "Meta"
+                | "NumLock"
+                | "PageDown"
+                | "PageUp"
+                | "Pause"
+                | "ScrollLock"
+                | "Shift"
+                | "Tab"
+        )
+}
+
+/// Web sends all all keys as strings, so it is up to us to figure out if it is
+/// a real text input or the name of a key.
+pub fn translate_key(key: &str) -> Option<egui::Key> {
+    match key {
+        "ArrowDown" => Some(egui::Key::ArrowDown),
+        "ArrowLeft" => Some(egui::Key::ArrowLeft),
+        "ArrowRight" => Some(egui::Key::ArrowRight),
+        "ArrowUp" => Some(egui::Key::ArrowUp),
+
+        "Esc" | "Escape" => Some(egui::Key::Escape),
+        "Tab" => Some(egui::Key::Tab),
+        "Backspace" => Some(egui::Key::Backspace),
+        "Enter" => Some(egui::Key::Enter),
+        "Space" | " " => Some(egui::Key::Space),
+
+        "Help" | "Insert" => Some(egui::Key::Insert),
+        "Delete" => Some(egui::Key::Delete),
+        "Home" => Some(egui::Key::Home),
+        "End" => Some(egui::Key::End),
+        "PageUp" => Some(egui::Key::PageUp),
+        "PageDown" => Some(egui::Key::PageDown),
+
+        "0" => Some(egui::Key::Num0),
+        "1" => Some(egui::Key::Num1),
+        "2" => Some(egui::Key::Num2),
+        "3" => Some(egui::Key::Num3),
+        "4" => Some(egui::Key::Num4),
+        "5" => Some(egui::Key::Num5),
+        "6" => Some(egui::Key::Num6),
+        "7" => Some(egui::Key::Num7),
+        "8" => Some(egui::Key::Num8),
+        "9" => Some(egui::Key::Num9),
+
+        "a" | "A" => Some(egui::Key::A),
+        "b" | "B" => Some(egui::Key::B),
+        "c" | "C" => Some(egui::Key::C),
+        "d" | "D" => Some(egui::Key::D),
+        "e" | "E" => Some(egui::Key::E),
+        "f" | "F" => Some(egui::Key::F),
+        "g" | "G" => Some(egui::Key::G),
+        "h" | "H" => Some(egui::Key::H),
+        "i" | "I" => Some(egui::Key::I),
+        "j" | "J" => Some(egui::Key::J),
+        "k" | "K" => Some(egui::Key::K),
+        "l" | "L" => Some(egui::Key::L),
+        "m" | "M" => Some(egui::Key::M),
+        "n" | "N" => Some(egui::Key::N),
+        "o" | "O" => Some(egui::Key::O),
+        "p" | "P" => Some(egui::Key::P),
+        "q" | "Q" => Some(egui::Key::Q),
+        "r" | "R" => Some(egui::Key::R),
+        "s" | "S" => Some(egui::Key::S),
+        "t" | "T" => Some(egui::Key::T),
+        "u" | "U" => Some(egui::Key::U),
+        "v" | "V" => Some(egui::Key::V),
+        "w" | "W" => Some(egui::Key::W),
+        "x" | "X" => Some(egui::Key::X),
+        "y" | "Y" => Some(egui::Key::Y),
+        "z" | "Z" => Some(egui::Key::Z),
+
+        _ => None,
+    }
+}
+
+pub fn modifiers_from_event(event: &web_sys::KeyboardEvent) -> egui::Modifiers {
+    egui::Modifiers {
+        alt: event.alt_key(),
+        ctrl: event.ctrl_key(),
+        shift: event.shift_key(),
+
+        // Ideally we should know if we are running or mac or not,
+        // but this works good enough for now.
+        mac_cmd: event.meta_key(),
+
+        // Ideally we should know if we are running or mac or not,
+        // but this works good enough for now.
+        command: event.ctrl_key() || event.meta_key(),
+    }
+}

eframe/src/web/mod.rs

@@ -0,0 +1,273 @@
+//! [`egui`] bindings for web apps (compiling to WASM).
+
+#![allow(clippy::missing_errors_doc)] // So many `-> Result<_, JsValue>`
+
+pub mod backend;
+mod events;
+mod glow_wrapping;
+mod input;
+pub mod screen_reader;
+pub mod storage;
+mod text_agent;
+
+pub use backend::*;
+pub use events::*;
+pub use storage::*;
+
+use std::collections::BTreeMap;
+use std::sync::{
+    atomic::{AtomicBool, Ordering},
+    Arc,
+};
+
+use egui::mutex::{Mutex, MutexGuard};
+use wasm_bindgen::prelude::*;
+use web_sys::EventTarget;
+
+use input::*;
+
+// ----------------------------------------------------------------------------
+
+/// Current time in seconds (since undefined point in time)
+pub fn now_sec() -> f64 {
+    web_sys::window()
+        .expect("should have a Window")
+        .performance()
+        .expect("should have a Performance")
+        .now()
+        / 1000.0
+}
+
+pub fn screen_size_in_native_points() -> Option<egui::Vec2> {
+    let window = web_sys::window()?;
+    Some(egui::vec2(
+        window.inner_width().ok()?.as_f64()? as f32,
+        window.inner_height().ok()?.as_f64()? as f32,
+    ))
+}
+
+pub fn native_pixels_per_point() -> f32 {
+    let pixels_per_point = web_sys::window().unwrap().device_pixel_ratio() as f32;
+    if pixels_per_point > 0.0 && pixels_per_point.is_finite() {
+        pixels_per_point
+    } else {
+        1.0
+    }
+}
+
+pub fn prefer_dark_mode() -> Option<bool> {
+    Some(
+        web_sys::window()?
+            .match_media("(prefers-color-scheme: dark)")
+            .ok()??
+            .matches(),
+    )
+}
+
+pub fn canvas_element(canvas_id: &str) -> Option<web_sys::HtmlCanvasElement> {
+    use wasm_bindgen::JsCast;
+    let document = web_sys::window()?.document()?;
+    let canvas = document.get_element_by_id(canvas_id)?;
+    canvas.dyn_into::<web_sys::HtmlCanvasElement>().ok()
+}
+
+pub fn canvas_element_or_die(canvas_id: &str) -> web_sys::HtmlCanvasElement {
+    canvas_element(canvas_id)
+        .unwrap_or_else(|| panic!("Failed to find canvas with id '{}'", canvas_id))
+}
+
+fn canvas_origin(canvas_id: &str) -> egui::Pos2 {
+    let rect = canvas_element(canvas_id)
+        .unwrap()
+        .get_bounding_client_rect();
+    egui::Pos2::new(rect.left() as f32, rect.top() as f32)
+}
+
+pub fn canvas_size_in_points(canvas_id: &str) -> egui::Vec2 {
+    let canvas = canvas_element(canvas_id).unwrap();
+    let pixels_per_point = native_pixels_per_point();
+    egui::vec2(
+        canvas.width() as f32 / pixels_per_point,
+        canvas.height() as f32 / pixels_per_point,
+    )
+}
+
+pub fn resize_canvas_to_screen_size(canvas_id: &str, max_size_points: egui::Vec2) -> Option<()> {
+    let canvas = canvas_element(canvas_id)?;
+
+    let screen_size_points = screen_size_in_native_points()?;
+    let pixels_per_point = native_pixels_per_point();
+
+    let max_size_pixels = pixels_per_point * max_size_points;
+
+    let canvas_size_pixels = pixels_per_point * screen_size_points;
+    let canvas_size_pixels = canvas_size_pixels.min(max_size_pixels);
+    let canvas_size_points = canvas_size_pixels / pixels_per_point;
+
+    // Make sure that the height and width are always even numbers.
+    // otherwise, the page renders blurry on some platforms.
+    // See https://github.com/emilk/egui/issues/103
+    fn round_to_even(v: f32) -> f32 {
+        (v / 2.0).round() * 2.0
+    }
+
+    canvas
+        .style()
+        .set_property(
+            "width",
+            &format!("{}px", round_to_even(canvas_size_points.x)),
+        )
+        .ok()?;
+    canvas
+        .style()
+        .set_property(
+            "height",
+            &format!("{}px", round_to_even(canvas_size_points.y)),
+        )
+        .ok()?;
+    canvas.set_width(round_to_even(canvas_size_pixels.x) as u32);
+    canvas.set_height(round_to_even(canvas_size_pixels.y) as u32);
+
+    Some(())
+}
+
+// ----------------------------------------------------------------------------
+
+pub fn set_cursor_icon(cursor: egui::CursorIcon) -> Option<()> {
+    let document = web_sys::window()?.document()?;
+    document
+        .body()?
+        .style()
+        .set_property("cursor", cursor_web_name(cursor))
+        .ok()
+}
+
+#[cfg(web_sys_unstable_apis)]
+pub fn set_clipboard_text(s: &str) {
+    if let Some(window) = web_sys::window() {
+        if let Some(clipboard) = window.navigator().clipboard() {
+            let promise = clipboard.write_text(s);
+            let future = wasm_bindgen_futures::JsFuture::from(promise);
+            let future = async move {
+                if let Err(err) = future.await {
+                    tracing::error!("Copy/cut action denied: {:?}", err);
+                }
+            };
+            wasm_bindgen_futures::spawn_local(future);
+        }
+    }
+}
+
+fn cursor_web_name(cursor: egui::CursorIcon) -> &'static str {
+    match cursor {
+        egui::CursorIcon::Alias => "alias",
+        egui::CursorIcon::AllScroll => "all-scroll",
+        egui::CursorIcon::Cell => "cell",
+        egui::CursorIcon::ContextMenu => "context-menu",
+        egui::CursorIcon::Copy => "copy",
+        egui::CursorIcon::Crosshair => "crosshair",
+        egui::CursorIcon::Default => "default",
+        egui::CursorIcon::Grab => "grab",
+        egui::CursorIcon::Grabbing => "grabbing",
+        egui::CursorIcon::Help => "help",
+        egui::CursorIcon::Move => "move",
+        egui::CursorIcon::NoDrop => "no-drop",
+        egui::CursorIcon::None => "none",
+        egui::CursorIcon::NotAllowed => "not-allowed",
+        egui::CursorIcon::PointingHand => "pointer",
+        egui::CursorIcon::Progress => "progress",
+        egui::CursorIcon::ResizeHorizontal => "ew-resize",
+        egui::CursorIcon::ResizeNeSw => "nesw-resize",
+        egui::CursorIcon::ResizeNwSe => "nwse-resize",
+        egui::CursorIcon::ResizeVertical => "ns-resize",
+
+        egui::CursorIcon::ResizeEast => "e-resize",
+        egui::CursorIcon::ResizeSouthEast => "se-resize",
+        egui::CursorIcon::ResizeSouth => "s-resize",
+        egui::CursorIcon::ResizeSouthWest => "sw-resize",
+        egui::CursorIcon::ResizeWest => "w-resize",
+        egui::CursorIcon::ResizeNorthWest => "nw-resize",
+        egui::CursorIcon::ResizeNorth => "n-resize",
+        egui::CursorIcon::ResizeNorthEast => "ne-resize",
+        egui::CursorIcon::ResizeColumn => "col-resize",
+        egui::CursorIcon::ResizeRow => "row-resize",
+
+        egui::CursorIcon::Text => "text",
+        egui::CursorIcon::VerticalText => "vertical-text",
+        egui::CursorIcon::Wait => "wait",
+        egui::CursorIcon::ZoomIn => "zoom-in",
+        egui::CursorIcon::ZoomOut => "zoom-out",
+    }
+}
+
+pub fn open_url(url: &str, new_tab: bool) -> Option<()> {
+    let name = if new_tab { "_blank" } else { "_self" };
+
+    web_sys::window()?
+        .open_with_url_and_target(url, name)
+        .ok()?;
+    Some(())
+}
+
+/// e.g. "#fragment" part of "www.example.com/index.html#fragment",
+///
+/// Percent decoded
+pub fn location_hash() -> String {
+    percent_decode(
+        &web_sys::window()
+            .unwrap()
+            .location()
+            .hash()
+            .unwrap_or_default(),
+    )
+}
+
+pub fn percent_decode(s: &str) -> String {
+    percent_encoding::percent_decode_str(s)
+        .decode_utf8_lossy()
+        .to_string()
+}
+
+// ----------------------------------------------------------------------------
+
+pub(crate) fn webgl1_requires_brightening(gl: &web_sys::WebGlRenderingContext) -> bool {
+    // See https://github.com/emilk/egui/issues/794
+
+    // detect WebKitGTK
+
+    // WebKitGTK use WebKit default unmasked vendor and renderer
+    // but safari use same vendor and renderer
+    // so exclude "Mac OS X" user-agent.
+    let user_agent = web_sys::window().unwrap().navigator().user_agent().unwrap();
+    !user_agent.contains("Mac OS X") && is_safari_and_webkit_gtk(gl)
+}
+
+/// detecting Safari and `webkitGTK`.
+///
+/// Safari and `webkitGTK` use unmasked renderer :Apple GPU
+///
+/// If we detect safari or `webkitGTKs` returns true.
+///
+/// This function used to avoid displaying linear color with `sRGB` supported systems.
+fn is_safari_and_webkit_gtk(gl: &web_sys::WebGlRenderingContext) -> bool {
+    // This call produces a warning in Firefox ("WEBGL_debug_renderer_info is deprecated in Firefox and will be removed.")
+    // but unless we call it we get errors in Chrome when we call `get_parameter` below.
+    // TODO: do something smart based on user agent?
+    if gl
+        .get_extension("WEBGL_debug_renderer_info")
+        .unwrap()
+        .is_some()
+    {
+        if let Ok(renderer) =
+            gl.get_parameter(web_sys::WebglDebugRendererInfo::UNMASKED_RENDERER_WEBGL)
+        {
+            if let Some(renderer) = renderer.as_string() {
+                if renderer.contains("Apple") {
+                    return true;
+                }
+            }
+        }
+    }
+
+    false
+}

eframe/src/web/screen_reader.rs

@@ -0,0 +1,49 @@
+pub struct ScreenReader {
+    #[cfg(feature = "screen_reader")]
+    tts: Option<tts::Tts>,
+}
+
+#[cfg(not(feature = "screen_reader"))]
+#[allow(clippy::derivable_impls)] // False positive
+impl Default for ScreenReader {
+    fn default() -> Self {
+        Self {}
+    }
+}
+
+#[cfg(feature = "screen_reader")]
+impl Default for ScreenReader {
+    fn default() -> Self {
+        let tts = match tts::Tts::default() {
+            Ok(screen_reader) => {
+                tracing::debug!("Initialized screen reader.");
+                Some(screen_reader)
+            }
+            Err(err) => {
+                tracing::warn!("Failed to load screen reader: {}", err);
+                None
+            }
+        };
+        Self { tts }
+    }
+}
+
+impl ScreenReader {
+    #[cfg(not(feature = "screen_reader"))]
+    #[allow(clippy::unused_self)]
+    pub fn speak(&mut self, _text: &str) {}
+
+    #[cfg(feature = "screen_reader")]
+    pub fn speak(&mut self, text: &str) {
+        if text.is_empty() {
+            return;
+        }
+        if let Some(tts) = &mut self.tts {
+            tracing::debug!("Speaking: {:?}", text);
+            let interrupt = true;
+            if let Err(err) = tts.speak(text, interrupt) {
+                tracing::warn!("Failed to read: {}", err);
+            }
+        }
+    }
+}

eframe/src/web/storage.rs

@@ -0,0 +1,43 @@
+fn local_storage() -> Option<web_sys::Storage> {
+    web_sys::window()?.local_storage().ok()?
+}
+
+pub fn local_storage_get(key: &str) -> Option<String> {
+    local_storage().map(|storage| storage.get_item(key).ok())??
+}
+
+pub fn local_storage_set(key: &str, value: &str) {
+    local_storage().map(|storage| storage.set_item(key, value));
+}
+
+#[cfg(feature = "persistence")]
+pub fn load_memory(ctx: &egui::Context) {
+    if let Some(memory_string) = local_storage_get("egui_memory_ron") {
+        match ron::from_str(&memory_string) {
+            Ok(memory) => {
+                *ctx.memory() = memory;
+            }
+            Err(err) => {
+                tracing::error!("Failed to parse memory RON: {}", err);
+            }
+        }
+    }
+}
+
+#[cfg(not(feature = "persistence"))]
+pub fn load_memory(_: &egui::Context) {}
+
+#[cfg(feature = "persistence")]
+pub fn save_memory(ctx: &egui::Context) {
+    match ron::to_string(&*ctx.memory()) {
+        Ok(ron) => {
+            local_storage_set("egui_memory_ron", &ron);
+        }
+        Err(err) => {
+            tracing::error!("Failed to serialize memory as RON: {}", err);
+        }
+    }
+}
+
+#[cfg(not(feature = "persistence"))]
+pub fn save_memory(_: &egui::Context) {}

eframe/src/web/text_agent.rs

@@ -0,0 +1,228 @@
+//! The text agent is an `<input>` element used to trigger
+//! mobile keyboard and IME input.
+
+use super::{canvas_element, AppRunner, AppRunnerContainer};
+use egui::mutex::MutexGuard;
+use std::cell::Cell;
+use std::rc::Rc;
+use wasm_bindgen::prelude::*;
+
+static AGENT_ID: &str = "egui_text_agent";
+
+pub fn text_agent() -> web_sys::HtmlInputElement {
+    use wasm_bindgen::JsCast;
+    web_sys::window()
+        .unwrap()
+        .document()
+        .unwrap()
+        .get_element_by_id(AGENT_ID)
+        .unwrap()
+        .dyn_into()
+        .unwrap()
+}
+
+/// Text event handler,
+pub fn install_text_agent(runner_container: &AppRunnerContainer) -> Result<(), JsValue> {
+    use wasm_bindgen::JsCast;
+    let window = web_sys::window().unwrap();
+    let document = window.document().unwrap();
+    let body = document.body().expect("document should have a body");
+    let input = document
+        .create_element("input")?
+        .dyn_into::<web_sys::HtmlInputElement>()?;
+    let input = std::rc::Rc::new(input);
+    input.set_id(AGENT_ID);
+    let is_composing = Rc::new(Cell::new(false));
+    {
+        let style = input.style();
+        // Transparent
+        style.set_property("opacity", "0").unwrap();
+        // Hide under canvas
+        style.set_property("z-index", "-1").unwrap();
+    }
+    // Set size as small as possible, in case user may click on it.
+    input.set_size(1);
+    input.set_autofocus(true);
+    input.set_hidden(true);
+
+    // When IME is off
+    runner_container.add_event_listener(&input, "input", {
+        let input_clone = input.clone();
+        let is_composing = is_composing.clone();
+
+        move |_event: web_sys::InputEvent, mut runner_lock| {
+            let text = input_clone.value();
+            if !text.is_empty() && !is_composing.get() {
+                input_clone.set_value("");
+                runner_lock.input.raw.events.push(egui::Event::Text(text));
+                runner_lock.needs_repaint.set_true();
+            }
+        }
+    })?;
+
+    {
+        // When IME is on, handle composition event
+        runner_container.add_event_listener(&input, "compositionstart", {
+            let input_clone = input.clone();
+            let is_composing = is_composing.clone();
+
+            move |_event: web_sys::CompositionEvent, mut runner_lock: MutexGuard<'_, AppRunner>| {
+                is_composing.set(true);
+                input_clone.set_value("");
+
+                runner_lock
+                    .input
+                    .raw
+                    .events
+                    .push(egui::Event::CompositionStart);
+                runner_lock.needs_repaint.set_true();
+            }
+        })?;
+
+        runner_container.add_event_listener(
+            &input,
+            "compositionupdate",
+            move |event: web_sys::CompositionEvent, mut runner_lock: MutexGuard<'_, AppRunner>| {
+                if let Some(event) = event.data().map(egui::Event::CompositionUpdate) {
+                    runner_lock.input.raw.events.push(event);
+                    runner_lock.needs_repaint.set_true();
+                }
+            },
+        )?;
+
+        runner_container.add_event_listener(&input, "compositionend", {
+            let input_clone = input.clone();
+
+            move |event: web_sys::CompositionEvent, mut runner_lock: MutexGuard<'_, AppRunner>| {
+                is_composing.set(false);
+                input_clone.set_value("");
+
+                if let Some(event) = event.data().map(egui::Event::CompositionEnd) {
+                    runner_lock.input.raw.events.push(event);
+                    runner_lock.needs_repaint.set_true();
+                }
+            }
+        })?;
+    }
+
+    // When input lost focus, focus on it again.
+    // It is useful when user click somewhere outside canvas.
+    runner_container.add_event_listener(
+        &input,
+        "focusout",
+        move |_event: web_sys::MouseEvent, _| {
+            // Delay 10 ms, and focus again.
+            let func = js_sys::Function::new_no_args(&format!(
+                "document.getElementById('{}').focus()",
+                AGENT_ID
+            ));
+            window
+                .set_timeout_with_callback_and_timeout_and_arguments_0(&func, 10)
+                .unwrap();
+        },
+    )?;
+
+    body.append_child(&input)?;
+
+    Ok(())
+}
+
+/// Focus or blur text agent to toggle mobile keyboard.
+pub fn update_text_agent(runner: MutexGuard<'_, AppRunner>) -> Option<()> {
+    use wasm_bindgen::JsCast;
+    use web_sys::HtmlInputElement;
+    let window = web_sys::window()?;
+    let document = window.document()?;
+    let input: HtmlInputElement = document.get_element_by_id(AGENT_ID)?.dyn_into().unwrap();
+    let canvas_style = canvas_element(runner.canvas_id())?.style();
+
+    if runner.mutable_text_under_cursor {
+        let is_already_editing = input.hidden();
+        if is_already_editing {
+            input.set_hidden(false);
+            input.focus().ok()?;
+
+            // Move up canvas so that text edit is shown at ~30% of screen height.
+            // Only on touch screens, when keyboard popups.
+            if let Some(latest_touch_pos) = runner.input.latest_touch_pos {
+                let window_height = window.inner_height().ok()?.as_f64()? as f32;
+                let current_rel = latest_touch_pos.y / window_height;
+
+                // estimated amount of screen covered by keyboard
+                let keyboard_fraction = 0.5;
+
+                if current_rel > keyboard_fraction {
+                    // below the keyboard
+
+                    let target_rel = 0.3;
+
+                    // Note: `delta` is negative, since we are moving the canvas UP
+                    let delta = target_rel - current_rel;
+
+                    let delta = delta.max(-keyboard_fraction); // Don't move it crazy much
+
+                    let new_pos_percent = format!("{}%", (delta * 100.0).round());
+
+                    canvas_style.set_property("position", "absolute").ok()?;
+                    canvas_style.set_property("top", &new_pos_percent).ok()?;
+                }
+            }
+        }
+    } else {
+        // Drop runner lock
+        drop(runner);
+
+        // Holding the runner lock while calling input.blur() causes a panic.
+        // This is most probably caused by the browser running the event handler
+        // for the triggered blur event synchronously, meaning that the mutex
+        // lock does not get dropped by the time another event handler is called.
+        //
+        // Why this didn't exist before #1290 is a mystery to me, but it exists now
+        // and this apparently is the fix for it
+        //
+        // ¯\_(ツ)_/¯ - @DusterTheFirst
+        input.blur().ok()?;
+
+        input.set_hidden(true);
+        canvas_style.set_property("position", "absolute").ok()?;
+        canvas_style.set_property("top", "0%").ok()?; // move back to normal position
+    }
+    Some(())
+}
+
+/// If context is running under mobile device?
+fn is_mobile() -> Option<bool> {
+    const MOBILE_DEVICE: [&str; 6] = ["Android", "iPhone", "iPad", "iPod", "webOS", "BlackBerry"];
+
+    let user_agent = web_sys::window()?.navigator().user_agent().ok()?;
+    let is_mobile = MOBILE_DEVICE.iter().any(|&name| user_agent.contains(name));
+    Some(is_mobile)
+}
+
+// Move text agent to text cursor's position, on desktop/laptop,
+// candidate window moves following text element (agent),
+// so it appears that the IME candidate window moves with text cursor.
+// On mobile devices, there is no need to do that.
+pub fn move_text_cursor(cursor: Option<egui::Pos2>, canvas_id: &str) -> Option<()> {
+    let style = text_agent().style();
+    // Note: movint agent on mobile devices will lead to unpredictable scroll.
+    if is_mobile() == Some(false) {
+        cursor.as_ref().and_then(|&egui::Pos2 { x, y }| {
+            let canvas = canvas_element(canvas_id)?;
+            let bounding_rect = text_agent().get_bounding_client_rect();
+            let y = (y + (canvas.scroll_top() + canvas.offset_top()) as f32)
+                .min(canvas.client_height() as f32 - bounding_rect.height() as f32);
+            let x = x + (canvas.scroll_left() + canvas.offset_left()) as f32;
+            // Canvas is translated 50% horizontally in html.
+            let x = (x - canvas.offset_width() as f32 / 2.0)
+                .min(canvas.client_width() as f32 - bounding_rect.width() as f32);
+            style.set_property("position", "absolute").ok()?;
+            style.set_property("top", &format!("{}px", y)).ok()?;
+            style.set_property("left", &format!("{}px", x)).ok()
+        })
+    } else {
+        style.set_property("position", "absolute").ok()?;
+        style.set_property("top", "0px").ok()?;
+        style.set_property("left", "0px").ok()
+    }
+}