add caret blink to input

crates/core/src/input.rs

@@ -11,7 +11,8 @@ use gpui::{
     EntityInputHandler, EventEmitter, Font, InteractiveElement as _, IntoElement, KeyBinding,
     KeyDownEvent, MouseButton, MouseDownEvent, MouseMoveEvent, MouseUpEvent, ParentElement as _,
     Pixels, RenderOnce, Role, SharedString, StatefulInteractiveElement as _, Styled as _,
-    TextAlign, TextRun, UTF16Selection, Window, actions, canvas, div, fill, point, px,
+    Subscription, TextAlign, TextRun, UTF16Selection, Window, actions, canvas, div, fill, point,
+    px,
 };
 use gpui_native_theme::{ActiveTheme as _, ColorTokens, Size};
 
@@ -21,6 +22,8 @@ use crate::common::{Sizable, h_flex};
 pub const INPUT_CONTEXT: &str = "Input";
 /// Consecutive edits within this interval merge into one undo entry.
 const DEFAULT_GROUP_INTERVAL: Duration = Duration::from_millis(300);
+/// How often the focused caret blinks.
+const CARET_BLINK_INTERVAL: Duration = Duration::from_millis(500);
 /// Maximum undo entries kept; the oldest drops off the front.
 const MAX_HISTORY: usize = 100;
 
@@ -316,6 +319,93 @@ impl HistoryEntry {
     }
 }
 
+/// Caret blink controller.
+struct CaretBlink {
+    interval: Duration,
+    generation: usize,
+    visible: bool,
+    active: bool,
+    paused: bool,
+}
+
+impl CaretBlink {
+    fn new(_cx: &mut Context<Self>) -> Self {
+        Self {
+            interval: CARET_BLINK_INTERVAL,
+            generation: 0,
+            visible: true,
+            active: false,
+            paused: false,
+        }
+    }
+
+    fn visible(&self) -> bool {
+        self.visible
+    }
+
+    /// Starts blinking; the caret shows first and hides after one interval.
+    fn enable(&mut self, cx: &mut Context<Self>) {
+        if self.active {
+            return;
+        }
+        self.active = true;
+        self.visible = true;
+        self.paused = false;
+        self.schedule(cx);
+    }
+
+    /// Stops blinking. The caret stays hidden; paint gates on focus anyway.
+    fn disable(&mut self, cx: &mut Context<Self>) {
+        self.active = false;
+        self.visible = false;
+        self.paused = false;
+        cx.notify();
+    }
+
+    /// Holds the caret visible and restarts the hide timer.
+    fn pause(&mut self, cx: &mut Context<Self>) {
+        if !self.active {
+            return;
+        }
+        if !self.visible {
+            self.visible = true;
+            cx.notify();
+        }
+        self.paused = true;
+        self.generation += 1;
+        self.schedule_pause(cx);
+    }
+
+    fn tick(&mut self, cx: &mut Context<Self>) {
+        if !self.active || self.paused {
+            return;
+        }
+        self.visible = !self.visible;
+        cx.notify();
+        self.schedule(cx);
+    }
+
+    fn schedule(&mut self, cx: &mut Context<Self>) {
+        self.generation += 1;
+        self.schedule_pause(cx);
+    }
+
+    fn schedule_pause(&mut self, cx: &mut Context<Self>) {
+        let generation = self.generation;
+        let interval = self.interval;
+        cx.spawn(async move |this, cx| {
+            cx.background_executor().timer(interval).await;
+            this.update(cx, |this, cx| {
+                if this.generation == generation {
+                    this.paused = false;
+                    this.tick(cx);
+                }
+            })
+        })
+        .detach();
+    }
+}
+
 /// Input state for a single-line text field.
 pub struct InputState {
     text: String,
@@ -341,15 +431,20 @@ pub struct InputState {
     group_interval: Duration,
     /// When set, user edits are refused, focus, movement, selection and copy stay.
     read_only: bool,
+    /// Drives the focused caret's blink.
+    caret_blink: Entity<CaretBlink>,
     /// The shaped line and element bounds, recorded during each paint,
     /// and shared with hit-testing and the IME geometry conversions.
     layout: Rc<RefCell<Option<InputLayout>>>,
+    /// Keeps the field repainting on blink ticks. Dropping it unsubscribes.
+    _caret_blink_subscription: Subscription,
 }
 
 impl EventEmitter<InputStateEvent> for InputState {}
 
 impl InputState {
-    fn new_inner(cx: &Context<Self>) -> Self {
+    fn new_inner(cx: &mut Context<Self>) -> Self {
+        let caret_blink = cx.new(CaretBlink::new);
         Self {
             text: String::new(),
             cursor: 0,
@@ -372,13 +467,15 @@ impl InputState {
             redo_stack: Vec::new(),
             group_interval: DEFAULT_GROUP_INTERVAL,
             read_only: false,
+            caret_blink: caret_blink.clone(),
             layout: Rc::new(RefCell::new(None)),
+            _caret_blink_subscription: cx.observe(&caret_blink, |_, _, cx| cx.notify()),
         }
     }
 
     /// Creates the state entity for an application-owned input.
     pub fn new(cx: &mut App) -> Entity<Self> {
-        cx.new(|cx| Self::new_inner(cx))
+        cx.new(Self::new_inner)
     }
 
     /// Creates the state entity with initial text, caret at the end.
@@ -522,6 +619,8 @@ impl InputState {
 
     fn notify(&mut self, window: &mut Window, cx: &mut Context<Self>) {
         cx.notify();
+        // Any change holds the caret solid and restarts the blink cycle.
+        self.caret_blink.update(cx, |blink, cx| blink.pause(cx));
         window.notify_text_input_changed(&self.focus_handle);
     }
 
@@ -532,6 +631,12 @@ impl InputState {
         }
         self.focused = focused;
 
+        if focused {
+            self.caret_blink.update(cx, |blink, cx| blink.enable(cx));
+        } else {
+            self.caret_blink.update(cx, |blink, cx| blink.disable(cx));
+        }
+
         cx.emit(if focused {
             InputStateEvent::Focused
         } else {
@@ -539,6 +644,11 @@ impl InputState {
         });
     }
 
+    /// Whether the caret should paint.
+    pub fn caret_visible(&mut self, focused: bool, cx: &mut Context<Self>) -> bool {
+        focused && !self.read_only && self.caret_blink.read(cx).visible()
+    }
+
     /// Replaces a byte range with `text` and collapses the caret to its end.
     fn replace_range(
         &mut self,
@@ -792,7 +902,7 @@ impl InputState {
         self.paint_text(origin, line_height, window, cx);
 
         // A caret promises that typing lands there; in read-only it does not.
-        if focused && !self.read_only && self.selection().is_empty() {
+        if focused && self.caret_visible(focused, cx) && self.selection().is_empty() {
             self.paint_caret(
                 origin,
                 caret_x,