add reveal text

crates/ui/src/message.rs

@@ -1,12 +1,13 @@
 use std::collections::BTreeMap;
 use std::rc::Rc;
+use std::time::Duration;
 
 use gpui::prelude::FluentBuilder as _;
 use gpui::{
-    AnyElement, App, ClickEvent, Context, ElementId, InteractiveElement as _, IntoElement,
-    MouseButton, MouseDownEvent, ObjectFit, ParentElement as _, RenderOnce, SharedString,
-    SharedUri, StatefulInteractiveElement as _, StyleRefinement, Styled, StyledImage, Window, div,
-    img, px,
+    Animation, AnimationExt as _, AnyElement, App, ClickEvent, Context, ElementId,
+    InteractiveElement as _, IntoElement, MouseButton, MouseDownEvent, ObjectFit,
+    ParentElement as _, RenderOnce, SharedString, SharedUri, StatefulInteractiveElement as _,
+    StyleRefinement, Styled, StyledImage, Window, div, img, px,
 };
 use gpui_kit::assets::IconName;
 use gpui_kit::component::button::{Button, ButtonVariants as _};
@@ -750,3 +751,44 @@ impl RenderOnce for MessageActions {
             .refine_style(&style)
     }
 }
+
+/// A message's text revealed word by word, paced by the estimated speech duration.
+#[derive(IntoElement)]
+pub struct RevealText {
+    text: SharedString,
+    duration: Duration,
+}
+
+impl RevealText {
+    pub fn new(text: impl Into<SharedString>, duration: Duration) -> Self {
+        Self {
+            text: text.into(),
+            duration,
+        }
+    }
+}
+
+impl RenderOnce for RevealText {
+    fn render(self, _window: &mut Window, _cx: &mut App) -> impl IntoElement {
+        let words: Vec<SharedString> = self
+            .text
+            .split_whitespace()
+            .map(SharedString::from)
+            .collect();
+        let total = words.len().max(1) as f32;
+
+        div().flex().flex_wrap().gap_x_1().with_animation(
+            "speech-reveal",
+            Animation::new(self.duration).with_max_fps(30.),
+            move |this, progress| {
+                let visible = ((progress * total).ceil() as usize).min(words.len());
+
+                this.children(words.iter().enumerate().map(|(ix, word)| {
+                    div()
+                        .when(ix >= visible, |this| this.invisible())
+                        .child(word.clone())
+                }))
+            },
+        )
+    }
+}