UI: status messages elide in the middle, the command line's placeholder fits its width

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/ui-egui/src/elide.rs

@@ -0,0 +1,84 @@
+//! Text that does not fit: elided in the middle, so both ends of a name stay readable
+//! (`F2:side:a5#[F2…]|F2:side:a6`), with the full text left to a hover.
+
+use std::borrow::Cow;
+
+use egui::{FontId, Ui};
+
+/// The ellipsis put in place of the middle.
+pub const ELLIPSIS: char = '…';
+
+/// `text`, or as much of its start and end as fits in `max_width` around an [`ELLIPSIS`].
+/// `width_of` measures a string as drawn. Ties keep one more character at the start. With no room
+/// even for the ellipsis alone, the ellipsis.
+pub fn middle<'a>(text: &'a str, max_width: f32, width_of: impl Fn(&str) -> f32) -> Cow<'a, str> {
+    if width_of(text) <= max_width {
+        return Cow::Borrowed(text);
+    }
+    let chars: Vec<char> = text.chars().collect();
+    let joined = |kept: usize| -> String {
+        let head = kept.div_ceil(2);
+        let tail = kept - head;
+        let mut s: String = chars.iter().take(head).collect();
+        s.push(ELLIPSIS);
+        s.extend(chars.iter().skip(chars.len() - tail));
+        s
+    };
+    // The widest that fits: the width grows with the characters kept.
+    let (mut lo, mut hi) = (0, chars.len().saturating_sub(1));
+    while lo < hi {
+        let mid = (lo + hi).div_ceil(2);
+        if width_of(&joined(mid)) <= max_width {
+            lo = mid;
+        } else {
+            hi = mid - 1;
+        }
+    }
+    Cow::Owned(joined(lo))
+}
+
+/// The width of `text` on one line in `font`.
+pub fn width(ui: &Ui, text: &str, font: &FontId) -> f32 {
+    ui.painter().layout_no_wrap(text.to_string(), font.clone(), egui::Color32::PLACEHOLDER).size().x
+}
+
+/// [`middle`] measured with `font` as `ui` draws it.
+pub fn middle_in<'a>(ui: &Ui, text: &'a str, font: &FontId, max_width: f32) -> Cow<'a, str> {
+    middle(text, max_width, |s| width(ui, s, font))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// One unit per character.
+    fn chars(s: &str) -> f32 {
+        s.chars().count() as f32
+    }
+
+    #[test]
+    fn fitting_text_is_kept_whole() {
+        assert!(matches!(middle("Seeds", 5.0, chars), Cow::Borrowed("Seeds")));
+    }
+
+    #[test]
+    fn long_text_keeps_both_ends() {
+        let name = "F2:side:a5#[F2:side:a6]|F2:side:a6";
+        let short = middle(name, 15.0, chars);
+        assert_eq!(short, "F2:side…side:a6");
+        assert!(chars(&short) <= 15.0);
+        assert_eq!(middle(name, 16.0, chars), "F2:side:…side:a6");
+    }
+
+    #[test]
+    fn no_room_leaves_the_ellipsis() {
+        assert_eq!(middle("abcdef", 1.0, chars), "…");
+        assert_eq!(middle("abcdef", 0.0, chars), "…");
+        assert_eq!(middle("", -1.0, chars), "…");
+    }
+
+    #[test]
+    fn multibyte_text_splits_on_characters() {
+        assert_eq!(middle("αβγδεζ", 4.0, chars), "αβ…ζ");
+    }
+}

crates/ui-egui/src/lib.rs

@@ -28,6 +28,7 @@ pub mod browser;
 pub mod capture;
 pub mod context;
 pub mod control;
+pub mod elide;
 pub mod fields;
 pub mod files;
 pub mod form;

crates/ui-egui/src/palette.rs

@@ -102,6 +102,28 @@ pub fn submit(app: &mut ModelApp, line: &str) {
     }
 }
 
+/// The command line's width: 40 % of the bar, within these.
+const MIN_LINE_W: f32 = 150.0;
+const MAX_LINE_W: f32 = 440.0;
+
+/// The command line's placeholders, longest first: the longest that fits whole is shown.
+const PLACEHOLDERS: [&str; 5] = [
+    r#"Type a command, e.g. mesh.node.add {"label": 1, "xyz": [0, 0, 0]} — or press S to search"#,
+    "Type a command, e.g. mesh.tet.generate — or press S to search",
+    "Type a command — or press S to search",
+    "Command, or S to search",
+    "Command",
+];
+
+/// The longest [`PLACEHOLDERS`] that fits a command line `width` wide, so it is never cut.
+fn placeholder(ui: &egui::Ui, width: f32) -> &'static str {
+    let font = egui::TextStyle::Body.resolve(ui.style());
+    // A text field's default margin is 4 points a side.
+    let room = width - 8.0;
+    let shortest = PLACEHOLDERS[PLACEHOLDERS.len() - 1];
+    PLACEHOLDERS.iter().copied().find(|p| crate::elide::width(ui, p, &font) <= room).unwrap_or(shortest)
+}
+
 /// The command line, the status and the model's size, above the timeline.
 pub fn command_line(app: &mut ModelApp, ui: &mut egui::Ui) {
     let t = Tokens::get(app.ui.dark);
@@ -112,11 +134,11 @@ pub fn command_line(app: &mut ModelApp, ui: &mut egui::Ui) {
             app.place("command_line", ui.max_rect());
             ui.horizontal_centered(|ui| {
                 ui.label(RichText::new("›").strong().color(t.accent));
+                // The rest of the bar keeps room for the status and the model's size.
+                let width = (ui.available_width() * 0.4).clamp(MIN_LINE_W, MAX_LINE_W);
+                let hint = if app.command_line.is_empty() { placeholder(ui, width) } else { "" };
                 let r = ui.add(
-                    egui::TextEdit::singleline(&mut app.command_line)
-                        .id(egui::Id::new("fc_command_line_text"))
-                        .hint_text(r#"Type a command, e.g. mesh.node.add {"label": 1, "xyz": [0, 0, 0]} — or press S to search"#)
-                        .desired_width(440.0),
+                    egui::TextEdit::singleline(&mut app.command_line).id(egui::Id::new("fc_command_line_text")).hint_text(hint).desired_width(width),
                 );
                 if r.lost_focus() && ui.input(|i| i.key_pressed(egui::Key::Enter)) {
                     let line = std::mem::take(&mut app.command_line);
@@ -134,7 +156,13 @@ pub fn command_line(app: &mut ModelApp, ui: &mut egui::Ui) {
                         Some(s) => (s.text.as_str(), if s.error { t.error } else { t.text }),
                         None => ("Ready", t.text_dim),
                     };
-                    ui.add(egui::Label::new(RichText::new(text).size(11.5).color(color)).truncate());
+                    // Elided in the middle (both the subject and the outcome stay), whole on hover.
+                    let font = FontId::proportional(11.5);
+                    let shown = crate::elide::middle_in(ui, text, &font, ui.available_width());
+                    let r = ui.add(egui::Label::new(RichText::new(shown.as_ref()).font(font).color(color)));
+                    if shown != text {
+                        r.on_hover_text(text);
+                    }
                 });
             });
         });