Add pointer events and focus handling for apps run in a Shadow DOM (#5627)

* [x] I have followed the instructions in the PR template

This PR handles pointer events and focus which did following changes:
- `element_from_point` and focus is now acquired from root node object
by using `get_root_node` from document or a shadow root.
- `TextAgent` is appended individually in each shadow root.

These changes handles pointer events and focus well in a web app that
are running in a shadow dom, or else the hover pointer actions and
keyboard input events are not triggered in a shadow dom.
Helpful for building embeddable/multi-view web-apps.

crates/eframe/Cargo.toml

@@ -253,6 +253,7 @@ web-sys = { workspace = true, features = [
   "ResizeObserverEntry",
   "ResizeObserverOptions",
   "ResizeObserverSize",
+  "ShadowRoot",
   "Storage",
   "Touch",
   "TouchEvent",

crates/eframe/src/web/events.rs

@@ -1,5 +1,3 @@
-use web_sys::EventTarget;
-
 use crate::web::string_from_js_value;
 
 use super::{
@@ -10,6 +8,8 @@ use super::{
     DEBUG_RESIZE,
 };
 
+use web_sys::{Document, EventTarget, ShadowRoot};
+
 // TODO(emilk): there are more calls to `prevent_default` and `stop_propagation`
 // than what is probably needed.
 
@@ -570,10 +570,17 @@ fn install_pointerup(runner_ref: &WebRunner, target: &EventTarget) -> Result<(),
 /// Returns true if the cursor is above the canvas, or if we're dragging something.
 /// Pass in the position in browser viewport coordinates (usually event.clientX/Y).
 fn is_interested_in_pointer_event(runner: &AppRunner, pos: egui::Pos2) -> bool {
-    let document = web_sys::window().unwrap().document().unwrap();
-    let is_hovering_canvas = document
-        .element_from_point(pos.x, pos.y)
-        .is_some_and(|element| element.eq(runner.canvas()));
+    let root_node = runner.canvas().get_root_node();
+
+    let element_at_point = if let Some(document) = root_node.dyn_ref::<Document>() {
+        document.element_from_point(pos.x, pos.y)
+    } else if let Some(shadow) = root_node.dyn_ref::<ShadowRoot>() {
+        shadow.element_from_point(pos.x, pos.y)
+    } else {
+        None
+    };
+
+    let is_hovering_canvas = element_at_point.is_some_and(|element| element.eq(runner.canvas()));
     let is_pointer_down = runner
         .egui_ctx()
         .input(|i| i.pointer.any_down() || i.any_touches());

crates/eframe/src/web/mod.rs

@@ -41,7 +41,7 @@ pub(crate) type ActiveWebPainter = web_painter_wgpu::WebPainterWgpu;
 pub use backend::*;
 
 use wasm_bindgen::prelude::*;
-use web_sys::MediaQueryList;
+use web_sys::{Document, MediaQueryList, Node};
 
 use input::{
     button_from_mouse_event, modifiers_from_kb_event, modifiers_from_mouse_event,
@@ -64,18 +64,22 @@ pub(crate) fn string_from_js_value(value: &JsValue) -> String {
 /// - `<a>`/`<area>` with an `href` attribute
 /// - `<input>`/`<select>`/`<textarea>`/`<button>` which aren't `disabled`
 /// - any other element with a `tabindex` attribute
-pub(crate) fn focused_element() -> Option<web_sys::Element> {
-    web_sys::window()?
-        .document()?
-        .active_element()?
-        .dyn_into()
-        .ok()
+pub(crate) fn focused_element(root: &Node) -> Option<web_sys::Element> {
+    if let Some(document) = root.dyn_ref::<Document>() {
+        document.active_element()
+    } else if let Some(shadow) = root.dyn_ref::<web_sys::ShadowRoot>() {
+        shadow.active_element()
+    } else {
+        None
+    }
 }
 
 pub(crate) fn has_focus<T: JsCast>(element: &T) -> bool {
     fn try_has_focus<T: JsCast>(element: &T) -> Option<bool> {
         let element = element.dyn_ref::<web_sys::Element>()?;
-        let focused_element = focused_element()?;
+        let root = element.get_root_node();
+
+        let focused_element = focused_element(&root)?;
         Some(element == &focused_element)
     }
     try_has_focus(element).unwrap_or(false)

crates/eframe/src/web/text_agent.rs

@@ -4,6 +4,7 @@
 use std::cell::Cell;
 
 use wasm_bindgen::prelude::*;
+use web_sys::{Document, Node};
 
 use super::{AppRunner, WebRunner};
 
@@ -14,7 +15,7 @@ pub struct TextAgent {
 
 impl TextAgent {
     /// Attach the agent to the document.
-    pub fn attach(runner_ref: &WebRunner) -> Result<Self, JsValue> {
+    pub fn attach(runner_ref: &WebRunner, root: Node) -> Result<Self, JsValue> {
         let document = web_sys::window().unwrap().document().unwrap();
 
         // create an `<input>` element
@@ -37,7 +38,17 @@ impl TextAgent {
         style.set_property("position", "absolute")?;
         style.set_property("top", "0")?;
         style.set_property("left", "0")?;
-        document.body().unwrap().append_child(&input)?;
+
+        if root.has_type::<Document>() {
+            // root object is a document, append to its body
+            root.dyn_into::<Document>()?
+                .body()
+                .unwrap()
+                .append_child(&input)?;
+        } else {
+            // append input into root directly
+            root.append_child(&input)?;
+        }
 
         // attach event listeners
 

crates/eframe/src/web/web_runner.rs

@@ -73,7 +73,7 @@ impl WebRunner {
 
         {
             // First set up the app runner:
-            let text_agent = TextAgent::attach(self)?;
+            let text_agent = TextAgent::attach(self, canvas.get_root_node())?;
             let app_runner =
                 AppRunner::new(canvas.clone(), web_options, app_creator, text_agent).await?;
             self.app_runner.replace(Some(app_runner));