From 40962a09ccc73ae06b1809b37d631797a2a5083a Mon Sep 17 00:00:00 2001
From: Nico Burns <nico@nicoburns.com>
Date: Tue, 8 Sep 2026 13:50:24 +0000
Subject: [PATCH] Enable IME for text inputs focussed before first layout

---
 packages/blitz-dom/src/document.rs     | 76 ++++++++++++++++++++++++++
 packages/blitz-dom/src/node/element.rs | 15 +++++
 packages/blitz-dom/src/node/node.rs    | 41 ++++++++------
 packages/blitz-dom/src/resolve.rs      |  5 ++
 4 files changed, 121 insertions(+), 16 deletions(-)

diff --git a/packages/blitz-dom/src/document.rs b/packages/blitz-dom/src/document.rs
index 313cb9c76..50c5ea52b 100644
--- a/packages/blitz-dom/src/document.rs
+++ b/packages/blitz-dom/src/document.rs
@@ -263,6 +263,8 @@ pub struct BaseDocument {
     pub(crate) last_client_pointer_position: Option<taffy::Point<f32>>,
     /// The node which is currently focussed (if any)
     pub(crate) focus_node_id: Option<NodeId>,
+    /// The IME cursor area most recently reported to the shell for the focussed text input
+    pub(crate) last_ime_cursor_area: Option<(f32, f32, f32, f32)>,
     /// The node which is currently active (if any)
     pub(crate) active_node_id: Option<NodeId>,
     /// The node which recieved a mousedown event (if any)
@@ -458,6 +460,7 @@ impl BaseDocument {
             hover_node_is_text: false,
             last_client_pointer_position: None,
             focus_node_id: None,
+            last_ime_cursor_area: None,
             active_node_id: None,
             mousedown_node_id: None,
             has_active_animations: false,
@@ -1672,10 +1675,25 @@ impl BaseDocument {
         );
 
         self.focus_node_id = Some(focus_node_id);
+        self.last_ime_cursor_area = self.nodes[focus_node_id].ime_cursor_area();
 
         true
     }
 
+    /// Report the focussed text input's content box to the shell as the IME cursor area,
+    /// if it has changed since it was last reported. Must be called after layout.
+    pub(crate) fn sync_ime_cursor_area(&mut self) {
+        let Some(node) = self.focus_node_id.and_then(|id| self.get_node(id)) else {
+            return;
+        };
+        let area = node.ime_cursor_area();
+        if let Some((x, y, width, height)) = area.filter(|a| Some(*a) != self.last_ime_cursor_area)
+        {
+            self.shell_provider.set_ime_cursor_area(x, y, width, height);
+            self.last_ime_cursor_area = area;
+        }
+    }
+
     pub fn active_node(&mut self) -> bool {
         let Some(hover_node_id) = self.get_hover_node_id() else {
             return false;
@@ -3296,3 +3314,61 @@ mod font_face_override_tests {
         );
     }
 }
+
+#[cfg(test)]
+mod ime_focus_tests {
+    use super::*;
+    use crate::qual_name;
+    use blitz_traits::shell::{ColorScheme, ShellProvider};
+    use std::sync::Mutex;
+
+    #[derive(Default)]
+    struct RecordingShell {
+        enabled: Mutex<Vec<bool>>,
+        areas: Mutex<Vec<(f32, f32, f32, f32)>>,
+    }
+    impl ShellProvider for RecordingShell {
+        fn set_ime_enabled(&self, is_enabled: bool) {
+            self.enabled.lock().unwrap().push(is_enabled);
+        }
+        fn set_ime_cursor_area(&self, x: f32, y: f32, width: f32, height: f32) {
+            self.areas.lock().unwrap().push((x, y, width, height));
+        }
+    }
+
+    /// An input focussed before the first layout (e.g. via `autofocus`) must still enable
+    /// the IME, and its cursor area must be reported once layout has run.
+    #[test]
+    fn focus_before_layout_enables_ime() {
+        let shell = Arc::new(RecordingShell::default());
+        let mut doc = BaseDocument::new(DocumentConfig {
+            viewport: Some(Viewport::new(400, 300, 1.0, ColorScheme::Light)),
+            shell_provider: Some(shell.clone()),
+            ..Default::default()
+        });
+        doc.add_user_agent_stylesheet("html, body { display: block; margin: 0 } input { display: block; width: 100px; height: 20px; padding: 0; border: 0 }");
+        let root_id = doc.root_node().id;
+        let mut mutator = doc.mutate();
+        let html = mutator.create_element(qual_name!("html"), vec![]);
+        let body = mutator.create_element(qual_name!("body"), vec![]);
+        let input = mutator.create_element(qual_name!("input"), vec![]);
+        mutator.append_children(body, &[input]);
+        mutator.append_children(html, &[body]);
+        mutator.append_children(root_id, &[html]);
+        drop(mutator);
+
+        doc.set_focus_to(input);
+        assert_eq!(*shell.enabled.lock().unwrap(), vec![true]);
+        assert!(shell.areas.lock().unwrap().is_empty());
+
+        doc.resolve(0.0);
+        assert_eq!(*shell.areas.lock().unwrap(), vec![(0.0, 0.0, 100.0, 20.0)]);
+
+        // Unchanged layout does not re-report the area
+        doc.resolve(0.0);
+        assert_eq!(shell.areas.lock().unwrap().len(), 1);
+
+        doc.clear_focus();
+        assert_eq!(*shell.enabled.lock().unwrap(), vec![true, false]);
+    }
+}
diff --git a/packages/blitz-dom/src/node/element.rs b/packages/blitz-dom/src/node/element.rs
index ccce2e186..8d40e69b6 100644
--- a/packages/blitz-dom/src/node/element.rs
+++ b/packages/blitz-dom/src/node/element.rs
@@ -476,6 +476,21 @@ impl ElementData {
         local_names!("button", "input", "select", "textarea").contains(&self.name.local)
     }
 
+    /// Whether this element is a `<textarea>` or an `<input>` of a type that takes text
+    /// input (and so gets a text editor and receives IME events). Unlike
+    /// [`text_input_data`](Self::text_input_data), this does not depend on layout
+    /// having run yet.
+    pub fn is_text_input(&self) -> bool {
+        if self.name.local == local_name!("textarea") {
+            return true;
+        }
+        self.name.local == local_name!("input")
+            && matches!(
+                self.attr(local_name!("type")),
+                None | Some("text" | "password" | "email" | "number" | "search" | "tel" | "url")
+            )
+    }
+
     /// Whether this element is a link (an `<a>` or `<area>` element with an `href` attribute)
     pub fn is_link(&self) -> bool {
         (self.name.local == local_name!("a") || self.name.local == local_name!("area"))
diff --git a/packages/blitz-dom/src/node/node.rs b/packages/blitz-dom/src/node/node.rs
index 3717cba6e..340e64f2e 100644
--- a/packages/blitz-dom/src/node/node.rs
+++ b/packages/blitz-dom/src/node/node.rs
@@ -667,21 +667,34 @@ impl Node {
         self.mark_ancestors_dirty();
 
         // If focussing a text input, enable IME and set IME area
-        if self
-            .element_data()
-            .and_then(|elem| elem.text_input_data())
-            .is_some()
-        {
+        if self.is_text_input() {
             shell_provider.set_ime_enabled(true);
-            let mut pos = self.absolute_position(0.0, 0.0);
-            pos.x += self.final_layout().content_box_x();
-            pos.y += self.final_layout().content_box_y();
-            let width = self.final_layout().content_box_width();
-            let height = self.final_layout().content_box_height();
-            shell_provider.set_ime_cursor_area(pos.x, pos.y, width, height);
+            if let Some((x, y, width, height)) = self.ime_cursor_area() {
+                shell_provider.set_ime_cursor_area(x, y, width, height);
+            }
         }
     }
 
+    /// Whether this node is a text input element (see [`ElementData::is_text_input`])
+    pub fn is_text_input(&self) -> bool {
+        self.element_data().is_some_and(|el| el.is_text_input())
+    }
+
+    /// The node's content box as `(x, y, width, height)` in CSS pixels, for use as the IME
+    /// cursor area. Returns `None` if the node is not a text input or has not been laid out
+    /// yet (e.g. it was focussed before the first layout).
+    pub fn ime_cursor_area(&self) -> Option<(f32, f32, f32, f32)> {
+        self.element_data()?.text_input_data()?;
+        let layout = self.final_layout();
+        let pos = self.absolute_position(0.0, 0.0);
+        Some((
+            pos.x + layout.content_box_x(),
+            pos.y + layout.content_box_y(),
+            layout.content_box_width(),
+            layout.content_box_height(),
+        ))
+    }
+
     pub fn blur(&mut self, shell_provider: Arc<dyn ShellProvider>) {
         if let Some(data) = self.element_data_mut() {
             data.element_state
@@ -690,11 +703,7 @@ impl Node {
         self.mark_ancestors_dirty();
 
         // If blurring a text input, disable IME
-        if self
-            .element_data()
-            .and_then(|elem| elem.text_input_data())
-            .is_some()
-        {
+        if self.is_text_input() {
             shell_provider.set_ime_enabled(false);
         }
     }
diff --git a/packages/blitz-dom/src/resolve.rs b/packages/blitz-dom/src/resolve.rs
index c89b73609..9b48f93ff 100644
--- a/packages/blitz-dom/src/resolve.rs
+++ b/packages/blitz-dom/src/resolve.rs
@@ -129,6 +129,11 @@ impl BaseDocument {
         // if the hovered node actually changes.
         self.refresh_hover();
 
+        // Keep the IME cursor area in sync with the (possibly moved) focussed text input.
+        // This also covers inputs focussed before their first layout (e.g. autofocus),
+        // for which `Node::focus` could not report an area.
+        self.sync_ime_cursor_area();
+
         let mut subdoc_is_animating = false;
         for &node_id in &self.sub_document_nodes {
             let node = &mut self.nodes[node_id];