feat(layout): overlay scrolling tab indicators and hover titles

compositor/src/config.rs

@@ -4,6 +4,7 @@ mod input_motion;
 mod layout;
 mod loading;
 mod outputs;
+mod tab_indicator;
 mod xwayland;
 
 use std::collections::{HashMap, HashSet};
@@ -28,6 +29,7 @@ use outputs::*;
 pub use outputs::{LidPolicy, OutputLayout, OutputModeRequest, OutputProfile, OutputSettings, OutputTransform};
 use serde::Deserialize;
 use smithay::input::keyboard::{Keycode, keysyms, xkb};
+pub(crate) use tab_indicator::TabIndicatorSettings;
 
 use crate::window_rules;
 use crate::window_rules::{WindowRule, WindowRuleConfig};
@@ -167,6 +169,7 @@ impl Config {
             focus_effect: self.focus_effect_settings()?,
             default_column_width: self.default_column_width()?,
             default_column_display: self.default_column_display(),
+            tab_indicator: self.tab_indicator_settings()?,
             scrolling_focus_strategy: self.scrolling_focus_strategy(),
             column_width_presets: self.width_presets()?,
             animations_enabled: self.animations_enabled(),
@@ -230,6 +233,8 @@ enum LayoutModeValue {
 
 #[derive(Debug, Default, Deserialize)]
 struct ScrollingConfig {
+    #[serde(default)]
+    tab_indicator: tab_indicator::TabIndicatorConfig,
     default_column_display: Option<ColumnDisplayValue>,
     default_column_width: Option<ColumnWidthValue>,
     focus_strategy: Option<FocusStrategyValue>,

compositor/src/config/tab_indicator.rs

@@ -0,0 +1,133 @@
+use super::*;
+
+#[derive(Clone, Debug, Deserialize)]
+#[serde(default, deny_unknown_fields)]
+pub(super) struct TabIndicatorConfig {
+    width: f64,
+    segment_height: f64,
+    segment_gap: f64,
+    hit_width: f64,
+    gap_threshold: f64,
+    list_width: f64,
+    row_height: f64,
+    padding: f64,
+    font_size: f64,
+    flash_duration_ms: u64,
+    active_color: Option<String>,
+    inactive_color: Option<String>,
+    background_color: Option<String>,
+    text_color: Option<String>,
+}
+
+impl Default for TabIndicatorConfig {
+    fn default() -> Self {
+        Self {
+            width: 4.0,
+            segment_height: 18.0,
+            segment_gap: 4.0,
+            hit_width: 12.0,
+            gap_threshold: 8.0,
+            list_width: 220.0,
+            row_height: 28.0,
+            padding: 4.0,
+            font_size: 12.0,
+            flash_duration_ms: 1000,
+            active_color: None,
+            inactive_color: None,
+            background_color: None,
+            text_color: None,
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct TabIndicatorSettings {
+    pub width: f64,
+    pub segment_height: f64,
+    pub segment_gap: f64,
+    pub hit_width: f64,
+    pub gap_threshold: f64,
+    pub list_width: f64,
+    pub row_height: f64,
+    pub padding: f64,
+    pub font_size: f64,
+    pub flash_duration: std::time::Duration,
+    pub active_color: Option<[f32; 4]>,
+    pub inactive_color: Option<[f32; 4]>,
+    pub background_color: Option<[f32; 4]>,
+    pub text_color: Option<[f32; 4]>,
+}
+
+impl Config {
+    pub(crate) fn tab_indicator_settings(&self) -> Result<TabIndicatorSettings, ConfigError> {
+        let c = &self.scrolling.tab_indicator;
+        let range = |value: f64, min: f64, max: f64, field: &'static str| {
+            if value.is_finite() && (min..=max).contains(&value) {
+                Ok(value)
+            } else {
+                Err(ConfigError::LayoutValue { field, value })
+            }
+        };
+        let color =
+            |value: &Option<String>, field| value.as_ref().map(|s| parse_color(s, field).map(|c| c.0)).transpose();
+        let width = range(c.width, 1.0, 16.0, "tab_indicator.width")?;
+        let hit_width = range(c.hit_width, width, 64.0, "tab_indicator.hit_width")?;
+        let font_size = range(c.font_size, 8.0, 32.0, "tab_indicator.font_size")?;
+        Ok(TabIndicatorSettings {
+            width,
+            hit_width,
+            font_size,
+            segment_height: range(c.segment_height, width, 128.0, "tab_indicator.segment_height")?,
+            segment_gap: range(c.segment_gap, 0.0, 64.0, "tab_indicator.segment_gap")?,
+            gap_threshold: range(c.gap_threshold, width, 128.0, "tab_indicator.gap_threshold")?,
+            list_width: range(c.list_width, 80.0, 640.0, "tab_indicator.list_width")?,
+            row_height: range(c.row_height, font_size + 6.0, 80.0, "tab_indicator.row_height")?,
+            padding: range(c.padding, 0.0, 24.0, "tab_indicator.padding")?,
+            flash_duration: std::time::Duration::from_millis(range(
+                c.flash_duration_ms as f64,
+                0.0,
+                60_000.0,
+                "tab_indicator.flash_duration_ms",
+            )? as u64),
+            active_color: color(&c.active_color, "tab_indicator.active_color")?,
+            inactive_color: color(&c.inactive_color, "tab_indicator.inactive_color")?,
+            background_color: color(&c.background_color, "tab_indicator.background_color")?,
+            text_color: color(&c.text_color, "tab_indicator.text_color")?,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn indicator_defaults_overrides_and_validation() {
+        let c = Config::parse_source("").unwrap().tab_indicator_settings().unwrap();
+        assert_eq!(
+            (c.width, c.segment_height, c.segment_gap, c.hit_width, c.gap_threshold),
+            (4., 18., 4., 12., 8.)
+        );
+        assert_eq!(c.flash_duration.as_millis(), 1000);
+        assert!(c.active_color.is_none());
+        let config = Config::parse_source(
+            "scrolling { tab-indicator { width 3; hit-width 14; flash-duration-ms 750; active-color \"#ff0000\"; }; }",
+        )
+        .unwrap();
+        let c = config.tab_indicator_settings().unwrap();
+        assert_eq!((c.width, c.hit_width, c.flash_duration.as_millis()), (3., 14., 750));
+        assert_eq!(c.active_color, Some([1., 0., 0., 1.]));
+        for source in [
+            "width 0",
+            "segment-gap -1",
+            "hit-width 2",
+            "row-height 8",
+            "flash-duration-ms 60001",
+            "active-color \"invalid\"",
+        ] {
+            let config = Config::parse_source(&format!("scrolling {{ tab-indicator {{ {source}; }}; }}")).unwrap();
+            assert!(config.tab_indicator_settings().is_err(), "{source}");
+        }
+        assert!(Config::parse_source("scrolling { tab-indicator { typo 1; }; }").is_err());
+    }
+}

compositor/src/input.rs

@@ -484,6 +484,7 @@ impl Ferese {
                 }
                 let position = self.constrain_pointer_position(&pointer, position);
 
+                self.update_tab_indicator_hover(position);
                 pointer.motion(
                     self,
                     self.surface_under(position),
@@ -528,6 +529,7 @@ impl Ferese {
                 let requested = self.clamp_pointer_position(position + delta);
                 let location = self.constrain_pointer_position(&pointer, requested);
 
+                self.update_tab_indicator_hover(location);
                 pointer.motion(
                     self,
                     self.surface_under(location),
@@ -712,6 +714,12 @@ impl Ferese {
                     return;
                 }
                 let pointer = self.seat.get_pointer().expect("seat has a pointer");
+                if self.scroll_tab_indicator(
+                    pointer.current_location(),
+                    if vertical != 0.0 { vertical } else { horizontal },
+                ) {
+                    return;
+                }
                 if self.scroll_overview_strip(
                     pointer.current_location(),
                     if horizontal != 0.0 { horizontal } else { vertical },

compositor/src/overview.rs

@@ -576,6 +576,16 @@ impl Ferese {
         Some(buffer)
     }
 
+    pub(crate) fn indicator_label(
+        &mut self,
+        text: &str,
+        scale: f64,
+        color: [f32; 4],
+        size: f64,
+    ) -> Option<LabelBuffer> {
+        self.overview.label_with_size(text, scale, color, size)
+    }
+
     pub(crate) fn overview_workspace_label(
         &mut self,
         index: u32,

compositor/src/render/mod.rs

@@ -11,6 +11,7 @@ mod overview;
 mod resources;
 mod scene;
 mod shader;
+mod tab_indicator;
 mod tabs;
 use std::collections::HashMap;
 use std::sync::Arc;
@@ -332,6 +333,10 @@ pub(crate) enum OverviewChromePart {
     Caption,
     Tab,
     TabActive,
+    TabRail,
+    TabList,
+    TabRow,
+    TabFlash,
 }
 
 #[derive(Debug)]

compositor/src/render/overview.rs

@@ -122,9 +122,13 @@ pub(super) fn overview_strip_elements(
         && let Some(cache) = state.render.outputs.get_mut(&output_id)
     {
         cache.chrome.retain(|(id, part), _| match part {
-            OverviewChromePart::Caption | OverviewChromePart::Tab | OverviewChromePart::TabActive => {
+            OverviewChromePart::Caption
-                state.windows.window(ferese_layout::WindowId(*id)).is_some()
+            | OverviewChromePart::Tab
-            }
+            | OverviewChromePart::TabActive
+            | OverviewChromePart::TabRail
+            | OverviewChromePart::TabList
+            | OverviewChromePart::TabRow
+            | OverviewChromePart::TabFlash => state.windows.window(ferese_layout::WindowId(*id)).is_some(),
             OverviewChromePart::Card | OverviewChromePart::Outline => card_ids.contains(id),
             OverviewChromePart::Strip => true,
         });

compositor/src/render/resources.rs

@@ -71,7 +71,16 @@ impl RenderResources {
         self.windows.remove(&id);
         for output in self.outputs.values_mut() {
             output.chrome.retain(|(key, part), _| {
-                *key != id.0 || !matches!(part, OverviewChromePart::Tab | OverviewChromePart::TabActive)
+                *key != id.0
+                    || !matches!(
+                        part,
+                        OverviewChromePart::Tab
+                            | OverviewChromePart::TabActive
+                            | OverviewChromePart::TabRail
+                            | OverviewChromePart::TabList
+                            | OverviewChromePart::TabRow
+                            | OverviewChromePart::TabFlash
+                    )
             });
         }
     }

compositor/src/render/tab_indicator.rs

@@ -0,0 +1,247 @@
+use super::*;
+use ferese_layout::{Rect, TabBar, WindowId};
+
+#[allow(clippy::too_many_arguments)]
+fn text_element(
+    state: &mut Ferese,
+    renderer: &mut GlesRenderer,
+    output_origin: Point<i32, Logical>,
+    scale: f64,
+    rect: Rect,
+    text: &str,
+    alpha: f32,
+    centered: bool,
+) -> Option<AnimatedWindowRenderElement> {
+    let settings = state.tab_indicator_settings;
+    let color = settings.text_color.unwrap_or(state.theme_settings.text_primary_color.0);
+    let limit = ((rect.width - 16.0) / (settings.font_size * 0.65)).floor().max(1.0) as usize;
+    let mut chars = text.chars().filter(|c| !c.is_control());
+    let mut title = chars.by_ref().take(limit).collect::<String>();
+    if chars.next().is_some() {
+        title.pop();
+        title.push('…');
+    }
+    let (buffer, size) = state.indicator_label(&title, scale, color, settings.font_size)?;
+    let x = if centered {
+        ((rect.width - f64::from(size.w) / scale) * 0.5).max(8.0)
+    } else {
+        8.0
+    };
+    let location = Point::<i32, Physical>::from((
+        ((rect.x - f64::from(output_origin.x) + x) * scale).round() as i32,
+        ((rect.y - f64::from(output_origin.y) + rect.height * 0.5) * scale).round() as i32 - size.h / 2,
+    ));
+    let element = MemoryRenderBufferRenderElement::from_buffer(
+        renderer,
+        location.to_f64(),
+        &buffer,
+        Some(alpha),
+        Some(Rectangle::from_size((f64::from(size.w), f64::from(size.h)).into())),
+        Some(
+            (
+                (f64::from(size.w) / scale).round() as i32,
+                (f64::from(size.h) / scale).round() as i32,
+            )
+                .into(),
+        ),
+        RenderElementKind::Unspecified,
+    )
+    .ok()?;
+    let element = RescaleRenderElement::from_element(element, location, 1.0);
+    let element = RelocateRenderElement::from_element(element, (0, 0), Relocate::Relative);
+    let clip = Rect::new(rect.x + 8.0, rect.y, (rect.width - 16.0).max(0.0), rect.height);
+    CropRenderElement::from_element(element, scale, physical_rect(clip, output_origin, scale)).map(Into::into)
+}
+
+fn title(state: &Ferese, id: WindowId, capture: bool) -> String {
+    if capture && state.windows.window(id).is_none_or(|w| state.capture_protected(w)) {
+        return "Protected window".into();
+    }
+    state
+        .windows
+        .record(id)
+        .map(|r| {
+            if !r.title.trim().is_empty() {
+                r.title.clone()
+            } else if !r.app_id.is_empty() {
+                r.app_id.clone()
+            } else {
+                "Window".into()
+            }
+        })
+        .unwrap_or_default()
+}
+
+#[allow(clippy::too_many_arguments)]
+pub(super) fn elements(
+    state: &mut Ferese,
+    renderer: &mut GlesRenderer,
+    output: &Output,
+    bar: &TabBar,
+    content: Rect,
+    alpha: f32,
+    capture: bool,
+) -> Vec<AnimatedWindowRenderElement> {
+    let Some(g) = state.tab_indicator_geometry(bar, content) else {
+        return Vec::new();
+    };
+    let Some(output_geometry) = state.space.output_geometry(output) else {
+        return Vec::new();
+    };
+    let scale = output.current_scale().fractional_scale();
+    let settings = state.tab_indicator_settings;
+    let anchor = bar.group.windows[0];
+    let accent = settings.active_color.unwrap_or(state.theme_settings.accent_color.0);
+    let inactive = settings.inactive_color.unwrap_or(state.theme_settings.border_color.0);
+    let background = settings
+        .background_color
+        .unwrap_or(state.theme_settings.surface_base_color.0);
+    let radius = state.theme_settings.material_radius;
+    let hover = state
+        .tab_indicator
+        .hover
+        .as_ref()
+        .filter(|h| h.anchor == anchor)
+        .map_or(0.0, |h| h.opacity.current.clamp(0.0, 1.0) as f32);
+    let flash = state
+        .tab_indicator
+        .flash
+        .as_ref()
+        .filter(|h| h.anchor == anchor)
+        .map_or(0.0, |h| h.opacity.current.clamp(0.0, 1.0) as f32);
+    let mut elements = Vec::new();
+    state.retain_overview_labels();
+    if hover > 0.0 {
+        let first = state
+            .tab_indicator
+            .first_row
+            .min(bar.group.windows.len().saturating_sub(g.rows));
+        for (row, id) in bar.group.windows.iter().copied().skip(first).take(g.rows).enumerate() {
+            let rect = g.row(row);
+            let label = title(state, id, capture);
+            if let Some(element) = text_element(
+                state,
+                renderer,
+                output_geometry.loc,
+                scale,
+                rect,
+                &label,
+                alpha * hover,
+                false,
+            ) {
+                elements.push(element);
+            }
+            if id == bar.group.active {
+                let mut fill = background;
+                for i in 0..3 {
+                    fill[i] += (accent[i] - fill[i]) * 0.2;
+                }
+                fill[3] = alpha * hover;
+                if let Some(element) = overview_chrome_element(
+                    state,
+                    renderer,
+                    output,
+                    output_geometry,
+                    scale,
+                    (id.0, OverviewChromePart::TabRow),
+                    rect,
+                    fill,
+                    0.0,
+                    (radius - g.padding).max(0.0).min(rect.height * 0.5),
+                ) {
+                    elements.push(element.into());
+                }
+            }
+        }
+        if let Some(element) = overview_chrome_element(
+            state,
+            renderer,
+            output,
+            output_geometry,
+            scale,
+            (anchor.0, OverviewChromePart::TabList),
+            g.list,
+            color_with_alpha(background, alpha * hover),
+            0.0,
+            radius.min(g.list.height * 0.5),
+        ) {
+            elements.push(element.into());
+        }
+    } else if flash > 0.0 {
+        let index = bar
+            .group
+            .windows
+            .iter()
+            .position(|id| *id == bar.group.active)
+            .unwrap_or(0);
+        let label = format!(
+            "{}/{} · {}",
+            index + 1,
+            bar.group.windows.len(),
+            title(state, bar.group.active, capture)
+        );
+        let width = (label.chars().count() as f64 * settings.font_size * 0.65 + 24.0).min(g.list.width);
+        let bounds = Rect::new(
+            output_geometry.loc.x as f64,
+            output_geometry.loc.y as f64,
+            output_geometry.size.w as f64,
+            output_geometry.size.h as f64,
+        );
+        let rect = Rect::new(
+            (content.x + (content.width - width) * 0.5).clamp(bounds.x, bounds.x + bounds.width - width),
+            (content.y + settings.padding).clamp(bounds.y, bounds.y + bounds.height - g.row_height),
+            width,
+            g.row_height,
+        );
+        if let Some(element) = text_element(
+            state,
+            renderer,
+            output_geometry.loc,
+            scale,
+            rect,
+            &label,
+            alpha * flash,
+            true,
+        ) {
+            elements.push(element);
+        }
+        if let Some(element) = overview_chrome_element(
+            state,
+            renderer,
+            output,
+            output_geometry,
+            scale,
+            (anchor.0, OverviewChromePart::TabFlash),
+            rect,
+            color_with_alpha(background, alpha * flash),
+            0.0,
+            rect.height * 0.5,
+        ) {
+            elements.push(element.into());
+        }
+    }
+    for (index, id) in bar.group.windows.iter().copied().enumerate() {
+        let rect = Rect::new(
+            g.rail.x,
+            g.rail.y + index as f64 * g.pitch,
+            g.rail.width,
+            g.segment_height,
+        );
+        let color = if id == bar.group.active { accent } else { inactive };
+        if let Some(element) = overview_chrome_element(
+            state,
+            renderer,
+            output,
+            output_geometry,
+            scale,
+            (id.0, OverviewChromePart::TabRail),
+            rect,
+            color_with_alpha(color, alpha),
+            0.0,
+            rect.width.min(rect.height) * 0.5,
+        ) {
+            elements.push(element.into());
+        }
+    }
+    elements
+}

compositor/src/render/tabs.rs

@@ -24,6 +24,20 @@ pub(super) fn tab_elements(
     let Some(sample) = frame.windows.get(&active) else {
         return Vec::new();
     };
+    if matches!(
+        state.workspaces.workspace(workspace).map(|w| &w.layout),
+        Some(ferese_core::WorkspaceLayout::Scrolling(_))
+    ) {
+        return super::tab_indicator::elements(
+            state,
+            renderer,
+            output,
+            &bar,
+            sample.presentation.bounds.current,
+            sample.presentation.alpha(),
+            capture,
+        );
+    }
     if bar.rect.height <= 0.0 {
         return Vec::new();
     }

compositor/src/state.rs

@@ -7,6 +7,7 @@ mod layout;
 mod navigation;
 mod outputs;
 mod reconciliation;
+pub(crate) mod tab_indicator;
 mod tabs;
 #[cfg(test)]
 mod window_lifecycle_tests;
@@ -456,6 +457,8 @@ pub struct Ferese {
     workspace_slides: HashMap<OutputId, WorkspaceSlide>,
     workspace_slide_offsets: HashMap<WorkspaceId, (f64, f64)>,
     pub focused_window: Option<WindowId>,
+    pub(crate) tab_indicator: tab_indicator::TabIndicatorState,
+    pub(crate) tab_indicator_settings: crate::config::TabIndicatorSettings,
     pub(crate) tab_bars: HashMap<WorkspaceId, Vec<ferese_layout::TabBar>>,
     pub(crate) tab_buttons: HashSet<u32>,
     pub(crate) focus_history: ferese_core::FocusHistory,
@@ -576,6 +579,7 @@ pub struct RuntimeConfig {
     pub focus_effect: crate::config::FocusEffectSettings,
     pub default_column_width: ColumnWidth,
     pub default_column_display: ferese_layout::ColumnDisplay,
+    pub(crate) tab_indicator: crate::config::TabIndicatorSettings,
     pub scrolling_focus_strategy: ViewportFocusStrategy,
     pub column_width_presets: Vec<ColumnWidth>,
     pub animations_enabled: bool,
@@ -752,6 +756,8 @@ impl Ferese {
             workspace_slides: HashMap::new(),
             workspace_slide_offsets: HashMap::new(),
             focused_window: None,
+            tab_indicator: tab_indicator::TabIndicatorState::default(),
+            tab_indicator_settings: config.tab_indicator,
             tab_bars: HashMap::new(),
             tab_buttons: HashSet::new(),
             focus_history: Default::default(),
@@ -980,6 +986,8 @@ impl Ferese {
         self.idle_inhibit = config.idle_inhibit;
         self.theme_settings = config.theme_settings;
         self.panel_corner_radius = config.panel_corner_radius;
+        self.tab_indicator_settings = config.tab_indicator;
+        self.clear_tab_indicator();
         self.panel_background_opacity = config.panel_background_opacity;
         self.panel_style = config.panel_style;
         self.focus_effect = config.focus_effect;

compositor/src/state/animation.rs

@@ -102,6 +102,7 @@ impl Ferese {
             || !self.dismissing_popups.is_empty()
             || self.render.snapshots().next().is_some()
             || self.overview.needs_tick()
+            || self.tab_indicator.is_animating()
         {
             return true;
         }
@@ -160,7 +161,9 @@ impl Ferese {
             self.release_presentation_dependencies();
         }
 
-        let mut active_animation = false;
+        let mut active_animation = self
+            .tab_indicator
+            .advance(delta, self.spring_config, self.animations_enabled);
         let mut completed_slides = Vec::new();
         for (output, slide) in &mut self.workspace_slides {
             if slide.held_progress.is_some() {

compositor/src/state/layout.rs

@@ -640,6 +640,7 @@ impl Ferese {
         self.rebuild_presentation_dependencies();
         self.sync_window_stacking();
         self.retarget_overview();
+        self.reconcile_tab_indicator();
         if !finalize {
             return;
         }

compositor/src/state/navigation.rs

@@ -197,6 +197,7 @@ impl Ferese {
         }
 
         self.relayout();
+        self.flash_tab_switch(current, next);
     }
 
     pub fn move_direction(&mut self, direction: Direction) {

compositor/src/state/prediction.rs

@@ -196,6 +196,7 @@ impl Ferese {
             .iter()
             .any(|window| Some(window.output) == self.output_id(output))
             || self.overview.is_animating(self.spring_config)
+            || self.tab_indicator_output_animating(output)
             || self
                 .dismissing_popups
                 .iter()

compositor/src/state/tab_indicator.rs

@@ -0,0 +1,558 @@
+use super::*;
+use crate::config::TabIndicatorSettings;
+use smithay::reexports::calloop::{
+    RegistrationToken,
+    timer::{TimeoutAction, Timer},
+};
+
+#[derive(Debug)]
+pub(crate) struct Overlay {
+    pub anchor: WindowId,
+    pub opacity: AnimatedValue,
+}
+
+#[derive(Debug, Default)]
+pub(crate) struct TabIndicatorState {
+    pub hover: Option<Overlay>,
+    pub flash: Option<Overlay>,
+    pub first_row: usize,
+    timer: Option<RegistrationToken>,
+}
+
+impl TabIndicatorState {
+    pub fn is_animating(&self) -> bool {
+        [&self.hover, &self.flash]
+            .into_iter()
+            .flatten()
+            .any(|o| o.opacity.is_animating())
+    }
+
+    pub fn advance(&mut self, delta: Duration, spring: SpringConfig, enabled: bool) -> bool {
+        let mut moving = false;
+        for overlay in [&mut self.hover, &mut self.flash] {
+            if let Some(value) = overlay {
+                if enabled {
+                    moving |= value
+                        .opacity
+                        .advance(delta, crate::presentation::emphasis_spring(spring));
+                } else {
+                    value.opacity.snap();
+                }
+                if !value.opacity.is_animating() && value.opacity.current == 0.0 {
+                    *overlay = None;
+                }
+            }
+        }
+        moving
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct IndicatorGeometry {
+    pub rail: Rect,
+    pub hit: Rect,
+    pub list: Rect,
+    pub segment_height: f64,
+    pub pitch: f64,
+    pub row_height: f64,
+    pub padding: f64,
+    pub rows: usize,
+}
+
+pub(crate) fn contains(rect: Rect, p: Point<f64, Logical>) -> bool {
+    p.x >= rect.x && p.x < rect.x + rect.width && p.y >= rect.y && p.y < rect.y + rect.height
+}
+
+impl IndicatorGeometry {
+    pub fn new(content: Rect, output: Rect, left_boundary: f64, count: usize, c: TabIndicatorSettings) -> Option<Self> {
+        if count < 2 || content.width <= 0.0 || content.height <= 0.0 || output.width <= 0.0 || output.height <= 0.0 {
+            return None;
+        }
+        let left = content.x.max(output.x);
+        let right = (content.x + content.width).min(output.x + output.width);
+        let top = content.y.max(output.y);
+        let bottom = (content.y + content.height).min(output.y + output.height);
+        if right - left < c.width || bottom <= top {
+            return None;
+        }
+        let gap = (content.x - left_boundary).max(0.0);
+        let x = if content.x >= output.x && gap >= c.gap_threshold {
+            content.x - (c.gap_threshold + c.width) * 0.5
+        } else {
+            left
+        }
+        .clamp(output.x, (right - c.width).max(output.x));
+        let natural = count as f64 * c.segment_height + count.saturating_sub(1) as f64 * c.segment_gap;
+        let fit = ((bottom - top) / natural).min(1.0);
+        let height = (natural * fit).min(bottom - top);
+        let rail = Rect::new(x, top + (bottom - top - height) * 0.5, c.width, height);
+        let hit_width = c.hit_width.min(output.width);
+        let hit = Rect::new(
+            (x + c.width * 0.5 - hit_width * 0.5).clamp(output.x, output.x + output.width - hit_width),
+            rail.y,
+            hit_width,
+            rail.height,
+        );
+        let padding = c.padding.min(output.height * 0.1).min(output.width * 0.1);
+        let row_height = c.row_height.min((output.height - 2.0 * padding).max(f64::EPSILON));
+        let rows = (((output.height - 2.0 * padding) / row_height).floor() as usize)
+            .max(1)
+            .min(count);
+        let list_width = c.list_width.min(output.width);
+        let list_height = (rows as f64 * row_height + 2.0 * padding).min(output.height);
+        let x = if hit.x + hit.width + padding + list_width <= output.x + output.width {
+            hit.x + hit.width + padding
+        } else if hit.x - padding - list_width >= output.x {
+            hit.x - padding - list_width
+        } else {
+            (hit.x + hit.width + padding).clamp(output.x, output.x + output.width - list_width)
+        };
+        let list = Rect::new(
+            x,
+            (rail.y + rail.height * 0.5 - list_height * 0.5).clamp(output.y, output.y + output.height - list_height),
+            list_width,
+            list_height,
+        );
+        Some(Self {
+            rail,
+            hit,
+            list,
+            segment_height: c.segment_height * fit,
+            pitch: (c.segment_height + c.segment_gap) * fit,
+            row_height,
+            padding,
+            rows,
+        })
+    }
+
+    pub fn row(&self, visible_index: usize) -> Rect {
+        Rect::new(
+            self.list.x + self.padding,
+            self.list.y + self.padding + visible_index as f64 * self.row_height,
+            (self.list.width - 2.0 * self.padding).max(0.0),
+            self.row_height,
+        )
+    }
+
+    pub fn hover_contains(&self, p: Point<f64, Logical>) -> bool {
+        let left = self.hit.x.min(self.list.x);
+        let top = self.hit.y.min(self.list.y);
+        contains(
+            Rect::new(
+                left,
+                top,
+                (self.hit.x + self.hit.width).max(self.list.x + self.list.width) - left,
+                (self.hit.y + self.hit.height).max(self.list.y + self.list.height) - top,
+            ),
+            p,
+        )
+    }
+}
+
+impl Ferese {
+    pub(crate) fn scrolling_tab_bar(&self, anchor: WindowId) -> Option<&ferese_layout::TabBar> {
+        let workspace = self.workspaces.workspace_for_window(anchor)?;
+        if !matches!(
+            self.workspaces.workspace(workspace)?.layout,
+            WorkspaceLayout::Scrolling(_)
+        ) {
+            return None;
+        }
+        self.visible_tab_bars(workspace)
+            .find(|bar| bar.group.windows.first() == Some(&anchor))
+    }
+
+    pub(crate) fn tab_indicator_geometry(
+        &self,
+        bar: &ferese_layout::TabBar,
+        content: Rect,
+    ) -> Option<IndicatorGeometry> {
+        let workspace = self.workspaces.workspace_for_window(bar.group.active)?;
+        let output_id = self.output_workspaces.output_for_workspace(workspace)?;
+        if self.output_workspaces.active_workspace(output_id) != Some(workspace) {
+            return None;
+        }
+        let output = self.outputs_by_id.get(&output_id)?;
+        let g = self.space.output_geometry(output)?;
+        let bounds = Rect::new(g.loc.x as f64, g.loc.y as f64, g.size.w as f64, g.size.h as f64);
+        let mut boundary = bounds.x;
+        // Measure the current visible gap, including animated column positions.
+        for window in self.space.elements() {
+            let Some(id) = self.windows.ids().get(window).copied() else {
+                continue;
+            };
+            if id == bar.group.active
+                || self.workspaces.workspace_for_window(id) != Some(workspace)
+                || !self.workspaces.workspace(workspace)?.layout.contains(id)
+            {
+                continue;
+            }
+            let Some(rect) = self.presented_window_rect(id) else {
+                continue;
+            };
+            if rect.x + rect.width <= content.x
+                && rect.y < content.y + content.height
+                && rect.y + rect.height > content.y
+            {
+                boundary = boundary.max(rect.x + rect.width);
+            }
+        }
+        IndicatorGeometry::new(
+            content,
+            bounds,
+            boundary,
+            bar.group.windows.len(),
+            self.tab_indicator_settings,
+        )
+    }
+
+    fn tab_indicator_can_hit(&self, active: WindowId, p: Point<f64, Logical>) -> bool {
+        if self.session_lock.active()
+            || self.input_capture.active()
+            || self.overview.is_presenting()
+            || self.seat.get_pointer().is_some_and(|p| p.is_grabbed())
+            || self.layer_surface_under(p, &[Layer::Overlay, Layer::Top]).is_some()
+        {
+            return false;
+        }
+        // Match the renderer's per-window stacking. An overlay can cover its
+        // own client and lower windows, never floating windows/popups above it.
+        for window in self.space.elements().rev() {
+            let Some(id) = self.windows.ids().get(window).copied() else {
+                continue;
+            };
+            if id == active {
+                break;
+            }
+            if self.presented_window_rect(id).is_some_and(|r| contains(r, p)) {
+                return false;
+            }
+        }
+        if self
+            .window_under_visual(p)
+            .is_some_and(|w| self.windows.ids().get(&w) == Some(&active))
+            && let Some((mut surface, _)) = self.window_surface_under(p)
+        {
+            while let Some(parent) = smithay::wayland::compositor::get_parent(&surface) {
+                surface = parent;
+            }
+            if self
+                .windows
+                .window(active)
+                .and_then(|w| w.toplevel())
+                .is_none_or(|t| t.wl_surface() != &surface)
+            {
+                return false;
+            }
+        }
+        true
+    }
+
+    pub(crate) fn indicator_tab_at(&self, p: Point<f64, Logical>) -> Option<WindowId> {
+        let workspace = self.workspace_under_pointer(p)?;
+        if !matches!(
+            self.workspaces.workspace(workspace)?.layout,
+            WorkspaceLayout::Scrolling(_)
+        ) {
+            return None;
+        }
+        for bar in self.visible_tab_bars(workspace) {
+            let Some(content) = self.presented_window_rect(bar.group.active) else {
+                continue;
+            };
+            let Some(g) = self.tab_indicator_geometry(bar, content) else {
+                continue;
+            };
+            if !self.tab_indicator_can_hit(bar.group.active, p) {
+                continue;
+            }
+            let anchor = bar.group.windows[0];
+            let expanded = self
+                .tab_indicator
+                .hover
+                .as_ref()
+                .is_some_and(|h| h.anchor == anchor && h.opacity.target > 0.0);
+            if expanded && contains(g.list, p) {
+                let first = self
+                    .tab_indicator
+                    .first_row
+                    .min(bar.group.windows.len().saturating_sub(g.rows));
+                let index = ((p.y - g.list.y - g.padding).max(0.0) / g.row_height).floor() as usize;
+                return bar.group.windows.get(first + index.min(g.rows - 1)).copied();
+            }
+            if contains(g.hit, p) {
+                let index = ((p.y - g.rail.y) / g.pitch).floor() as usize;
+                return bar.group.windows.get(index.min(bar.group.windows.len() - 1)).copied();
+            }
+            if expanded && g.hover_contains(p) {
+                return Some(bar.group.active);
+            }
+        }
+        None
+    }
+
+    pub(crate) fn update_tab_indicator_hover(&mut self, p: Point<f64, Logical>) {
+        let anchor = self.indicator_tab_at(p).and_then(|id| {
+            self.workspaces
+                .workspace_for_window(id)
+                .and_then(|ws| self.workspaces.workspace(ws))
+                .and_then(|ws| ws.layout.tab_group(id))
+                .and_then(|group| group.windows.first().copied())
+        });
+        let unchanged = match (anchor, &self.tab_indicator.hover) {
+            (Some(anchor), Some(hover)) => hover.anchor == anchor && hover.opacity.target == 1.0,
+            (None, Some(hover)) => hover.opacity.target == 0.0,
+            (None, None) => true,
+            _ => false,
+        };
+        if unchanged {
+            return;
+        }
+        self.advance_animations(Instant::now());
+        if let Some(anchor) = anchor {
+            let same = self.tab_indicator.hover.as_ref().is_some_and(|h| h.anchor == anchor);
+            if !same {
+                let selected = self
+                    .scrolling_tab_bar(anchor)
+                    .and_then(|bar| {
+                        let g = self.tab_indicator_geometry(bar, self.presented_window_rect(bar.group.active)?)?;
+                        let selected = bar.group.windows.iter().position(|id| *id == bar.group.active)?;
+                        Some(
+                            selected
+                                .saturating_sub(g.rows / 2)
+                                .min(bar.group.windows.len().saturating_sub(g.rows)),
+                        )
+                    })
+                    .unwrap_or(0);
+                self.tab_indicator.first_row = selected;
+                self.tab_indicator.hover = Some(Overlay {
+                    anchor,
+                    opacity: AnimatedValue::new(0.0),
+                });
+            }
+            if let Some(hover) = &mut self.tab_indicator.hover {
+                if hover.opacity.target == 1.0 {
+                    return;
+                }
+                hover.opacity.retarget_preserving_motion(1.0);
+                if !self.animations_enabled {
+                    hover.opacity.snap();
+                }
+            }
+        } else if let Some(hover) = &mut self.tab_indicator.hover {
+            if hover.opacity.target == 0.0 {
+                return;
+            }
+            hover.opacity.retarget_preserving_motion(0.0);
+            if !self.animations_enabled {
+                hover.opacity.snap();
+            }
+        } else {
+            return;
+        }
+        crate::backends::direct::render_all(self);
+    }
+
+    pub(crate) fn scroll_tab_indicator(&mut self, p: Point<f64, Logical>, amount: f64) -> bool {
+        let Some(hover) = &self.tab_indicator.hover else {
+            return false;
+        };
+        if hover.opacity.target == 0.0 || self.indicator_tab_at(p).is_none() {
+            return false;
+        }
+        let Some(bar) = self.scrolling_tab_bar(hover.anchor) else {
+            return false;
+        };
+        let Some(content) = self.presented_window_rect(bar.group.active) else {
+            return false;
+        };
+        let Some(g) = self.tab_indicator_geometry(bar, content) else {
+            return false;
+        };
+        let max = bar.group.windows.len().saturating_sub(g.rows);
+        if amount != 0.0 {
+            self.tab_indicator.first_row = if amount > 0.0 {
+                self.tab_indicator.first_row.saturating_add(1).min(max)
+            } else {
+                self.tab_indicator.first_row.saturating_sub(1).min(max)
+            };
+            crate::backends::direct::render_all(self);
+        }
+        true
+    }
+
+    pub(crate) fn flash_tab_switch(&mut self, previous: WindowId, current: WindowId) {
+        if previous == current {
+            return;
+        }
+        let Some(workspace) = self
+            .workspaces
+            .workspace_for_window(current)
+            .and_then(|ws| self.workspaces.workspace(ws))
+        else {
+            return;
+        };
+        let WorkspaceLayout::Scrolling(layout) = &workspace.layout else {
+            return;
+        };
+        let Some(group) = layout.tab_group(current).filter(|g| g.windows.contains(&previous)) else {
+            return;
+        };
+        if self.tab_indicator_settings.flash_duration.is_zero() {
+            return;
+        }
+        let anchor = group.windows[0];
+        if let Some(token) = self.tab_indicator.timer.take() {
+            self.loop_handle.remove(token);
+        }
+        if let Some(flash) = self.tab_indicator.flash.as_mut().filter(|f| f.anchor == anchor) {
+            flash.opacity.retarget_preserving_motion(1.0);
+        } else {
+            let mut opacity = AnimatedValue::new(0.0);
+            opacity.set_target(1.0);
+            self.tab_indicator.flash = Some(Overlay { anchor, opacity });
+        }
+        if !self.animations_enabled
+            && let Some(flash) = &mut self.tab_indicator.flash
+        {
+            flash.opacity.snap();
+        }
+        match self.loop_handle.insert_source(
+            Timer::from_duration(self.tab_indicator_settings.flash_duration),
+            |_, _, state| {
+                state.tab_indicator.timer = None;
+                if let Some(flash) = &mut state.tab_indicator.flash {
+                    flash.opacity.set_target(0.0);
+                    if !state.animations_enabled {
+                        flash.opacity.snap();
+                    }
+                }
+                crate::backends::direct::render_all(state);
+                TimeoutAction::Drop
+            },
+        ) {
+            Ok(token) => self.tab_indicator.timer = Some(token),
+            Err(error) => {
+                self.tab_indicator.flash = None;
+                tracing::warn!(%error, "could not schedule tab feedback");
+            }
+        }
+        crate::backends::direct::render_all(self);
+    }
+
+    pub(crate) fn reconcile_tab_indicator(&mut self) {
+        if self.session_lock.active() || self.input_capture.active() || self.overview.is_presenting() {
+            self.clear_tab_indicator();
+            return;
+        }
+        if self
+            .tab_indicator
+            .hover
+            .as_ref()
+            .is_some_and(|h| self.scrolling_tab_bar(h.anchor).is_none())
+        {
+            self.tab_indicator.hover = None;
+        }
+        if self
+            .tab_indicator
+            .flash
+            .as_ref()
+            .is_some_and(|h| self.scrolling_tab_bar(h.anchor).is_none())
+        {
+            self.tab_indicator.flash = None;
+            if let Some(token) = self.tab_indicator.timer.take() {
+                self.loop_handle.remove(token);
+            }
+        }
+    }
+
+    pub(crate) fn clear_tab_indicator(&mut self) {
+        if let Some(token) = self.tab_indicator.timer.take() {
+            self.loop_handle.remove(token);
+        }
+        self.tab_indicator = TabIndicatorState::default();
+    }
+
+    pub(crate) fn tab_indicator_output_animating(&self, output: &Output) -> bool {
+        [&self.tab_indicator.hover, &self.tab_indicator.flash]
+            .into_iter()
+            .flatten()
+            .any(|o| o.opacity.is_animating() && self.window_belongs_to_output(o.anchor, output))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn settings() -> TabIndicatorSettings {
+        crate::config::Config::parse_source("")
+            .unwrap()
+            .tab_indicator_settings()
+            .unwrap()
+    }
+
+    #[test]
+    fn rail_uses_gap_or_inner_edge_without_changing_content_geometry() {
+        let content = Rect::new(100.25, 20.5, 400., 300.);
+        let output = Rect::new(0., 0., 800., 600.);
+        let c = settings();
+        for gap in [0., 7.99, 8., 24.] {
+            let g = IndicatorGeometry::new(content, output, content.x - gap, 3, c).unwrap();
+            assert_eq!(
+                (g.rail.width, g.rail.height, g.segment_height, g.pitch),
+                (4., 62., 18., 22.)
+            );
+            assert_eq!(g.rail.y, content.y + (content.height - 62.) * 0.5);
+            assert_eq!(g.hit.width, 12.);
+            if gap >= 8. {
+                assert!(g.rail.x >= content.x - gap && g.rail.x + g.rail.width <= content.x);
+            } else {
+                assert!(g.rail.x >= content.x && g.rail.x + g.rail.width <= content.x + 12.);
+            }
+            assert!(g.hover_contains((g.hit.x + g.hit.width, g.rail.y + 2.).into()));
+        }
+        assert!(IndicatorGeometry::new(content, output, 0., 1, c).is_none());
+    }
+
+    #[test]
+    fn overflow_and_fractional_output_edges_keep_list_and_rail_reachable() {
+        for output in [
+            Rect::new(-800.25, 10.5, 800., 600.),
+            Rect::new(0., 0., 100., 40.),
+            Rect::new(0., 0., 8., 0.5),
+        ] {
+            let content = Rect::new(output.x - 20., output.y, output.width + 40., output.height);
+            let g = IndicatorGeometry::new(content, output, output.x, 100, settings()).unwrap();
+            for rect in [g.rail, g.hit, g.list] {
+                assert!(rect.x >= output.x && rect.y >= output.y);
+                assert!(rect.x + rect.width <= output.x + output.width + 1e-8);
+                assert!(rect.y + rect.height <= output.y + output.height + 1e-8);
+            }
+            assert!(g.rows < 100 && g.rows > 0);
+            assert!(g.segment_height > 0.);
+        }
+    }
+
+    #[test]
+    fn interrupted_hover_spring_keeps_motion_and_settles_without_background_ticks() {
+        let mut state = TabIndicatorState {
+            hover: Some(Overlay {
+                anchor: WindowId(1),
+                opacity: AnimatedValue::new(0.),
+            }),
+            ..Default::default()
+        };
+        state.hover.as_mut().unwrap().opacity.set_target(1.);
+        state.advance(Duration::from_millis(30), SpringConfig::default(), true);
+        let before = state.hover.as_ref().unwrap().opacity;
+        state.hover.as_mut().unwrap().opacity.retarget_preserving_motion(0.);
+        let after = state.hover.as_ref().unwrap().opacity;
+        assert_eq!((before.current, before.velocity), (after.current, after.velocity));
+        for _ in 0..300 {
+            state.advance(Duration::from_millis(16), SpringConfig::default(), true);
+        }
+        assert!(state.hover.is_none());
+        assert!(!state.is_animating());
+    }
+}

compositor/src/state/tabs.rs

@@ -71,8 +71,10 @@ impl Ferese {
         if self.workspaces.active().fullscreen.is_some() {
             return;
         }
-        if let Some(target) = self.workspaces.active().layout.adjacent_tab(window, previous) {
+        if let Some(target) = self.workspaces.active().layout.adjacent_tab(window, previous)
-            self.activate_managed_window(target);
+            && self.activate_managed_window(target)
+        {
+            self.flash_tab_switch(window, target);
         }
     }
 
@@ -100,6 +102,12 @@ impl Ferese {
             return None;
         }
         let workspace = self.workspace_under_pointer(position)?;
+        if matches!(
+            self.workspaces.workspace(workspace)?.layout,
+            WorkspaceLayout::Scrolling(_)
+        ) {
+            return self.indicator_tab_at(position);
+        }
         // Floating windows and popups in front of the group keep their input.
         if self.window_surface_under(position).is_some() {
             return None;

compositor/src/state/window_lifecycle_tests.rs

@@ -1073,3 +1073,101 @@ fn scrolling_tabs_switch_with_directional_focus_and_drop_hidden_resize_holds() {
     assert_eq!(state.space.elements().count(), 2);
     assert_eq!(state.tab_bars[&workspace][0].group.windows, [a, b]);
 }
+
+#[test]
+fn tab_indicator_hover_switch_and_flash_preserve_window_geometry() {
+    if !crate::startup_tests::private_runtime(
+        "state::window_lifecycle_tests::tab_indicator_hover_switch_and_flash_preserve_window_geometry",
+    ) {
+        return;
+    }
+    let (mut events, mut state, _output) = fixture();
+    let (first, _first_wire) = window(&mut state, &mut events, 0xff112233);
+    state.toggle_column_tabbed();
+    let (second, _second_wire) = window(&mut state, &mut events, 0xff445566);
+    state.consume_focused_window();
+    let a = state.windows.ids()[&first];
+    let b = state.windows.ids()[&second];
+    let workspace = state.workspaces.active_id();
+    let bar = state.tab_bars[&workspace][0].clone();
+    let before = state.windows.geometry(&b).unwrap().logical;
+    let g = state
+        .tab_indicator_geometry(&bar, state.presented_window_rect(b).unwrap())
+        .unwrap();
+    let point = (g.hit.x + g.hit.width * 0.5, g.rail.y + g.segment_height * 0.5).into();
+    assert_eq!(state.tab_at(point), Some(a));
+    assert!(
+        state.surface_under(point).is_none(),
+        "the rail must not deliver input to the client"
+    );
+    state.update_tab_indicator_hover(point);
+    assert_eq!(state.tab_indicator.hover.as_ref().unwrap().opacity.current, 1.);
+    assert_eq!(state.windows.geometry(&b).unwrap().logical, before);
+    let row = g.row(0);
+    let point = (row.x + row.width * 0.5, row.y + row.height * 0.5).into();
+    state.update_tab_indicator_hover(point);
+    assert_eq!(state.tab_at(point), Some(a));
+    state.activate_managed_window(a);
+    assert_eq!(state.windows.geometry(&a).unwrap().logical, before);
+    assert!(state.tab_indicator.flash.is_none(), "pointer activation does not flash");
+    state.update_tab_indicator_hover((799., 599.).into());
+    assert_eq!(state.tab_indicator.hover.as_ref().unwrap().opacity.current, 0.);
+    state.tab_indicator_settings.flash_duration = Duration::from_millis(1);
+    state.cycle_tab(false);
+    assert_eq!(state.focused_window, Some(b));
+    assert_eq!(state.tab_indicator.flash.as_ref().unwrap().opacity.current, 1.);
+    assert_eq!(state.windows.geometry(&b).unwrap().logical, before);
+    let deadline = Instant::now() + Duration::from_secs(1);
+    while state
+        .tab_indicator
+        .flash
+        .as_ref()
+        .is_some_and(|f| f.opacity.target != 0.)
+        && Instant::now() < deadline
+    {
+        events.dispatch(Duration::from_millis(5), &mut state).unwrap();
+    }
+    assert_eq!(state.tab_indicator.flash.as_ref().unwrap().opacity.current, 0.);
+    state.toggle_column_tabbed();
+    assert!(state.tab_indicator.hover.is_none());
+    assert!(state.tab_indicator.flash.is_none());
+    assert!(state.tab_at(point).is_none());
+}
+
+#[test]
+fn tab_indicator_yields_to_a_floating_window_and_disappears_with_one_tab() {
+    if !crate::startup_tests::private_runtime(
+        "state::window_lifecycle_tests::tab_indicator_yields_to_a_floating_window_and_disappears_with_one_tab",
+    ) {
+        return;
+    }
+    let (mut events, mut state, _output) = fixture();
+    let (first, _first_wire) = window(&mut state, &mut events, 0xff112233);
+    state.toggle_column_tabbed();
+    let (second, _second_wire) = window(&mut state, &mut events, 0xff445566);
+    state.consume_focused_window();
+    let a = state.windows.ids()[&first];
+    let b = state.windows.ids()[&second];
+    let workspace = state.workspaces.active_id();
+    let (overlay, _overlay_wire) = window(&mut state, &mut events, 0xff778899);
+    let overlay_id = state.windows.ids()[&overlay];
+    state.toggle_focused_floating();
+    let bar = state.tab_bars[&workspace][0].clone();
+    let g = state
+        .tab_indicator_geometry(&bar, state.presented_window_rect(b).unwrap())
+        .unwrap();
+    let point = (g.hit.x + 6., g.hit.y + 5.).into();
+    state
+        .workspaces
+        .set_floating_rect(overlay_id, Rect::new(g.hit.x, g.hit.y, 200., 100.))
+        .unwrap();
+    state.relayout();
+    assert!(
+        state.tab_at(point).is_none(),
+        "floating window above the rail keeps its pointer input"
+    );
+    state.activate_managed_window(b);
+    state.leave_tab();
+    assert!(state.scrolling_tab_bar(a).is_none());
+    assert!(state.tab_indicator.hover.is_none());
+}

crates/ferese-layout/src/scrolling.rs

@@ -834,16 +834,11 @@ impl ScrollingLayout {
             let (column_x, column_width) = column_positions[column_index];
             if column.display == ColumnDisplay::Tabbed {
                 let window = column.windows[column.active];
-                let header = if column.windows.len() > 1 {
-                    crate::TAB_BAR_HEIGHT.min((viewport_height - 1.0).max(0.0))
-                } else {
-                    0.0
-                };
                 let mut rect = Rect::new(
                     bounds.x + outer + column_x - self.viewport_x,
-                    bounds.y + outer + header,
+                    bounds.y + outer,
                     column_width,
-                    viewport_height - header,
+                    viewport_height,
                 );
                 // All tabs use one size, even when their client constraints differ.
                 // Keep the column allocation stable and honor compatible maximums.
@@ -864,13 +859,13 @@ impl ScrollingLayout {
                 let common = normalized_constraints(common);
                 record_minimum_warnings(window, rect, common, &mut result.warnings);
                 apply_maximums(window, &mut rect, common, &mut result.warnings);
-                if header > 0.0 {
+                if column.windows.len() > 1 {
                     result.tab_bars.push(crate::TabBar {
                         group: crate::TabGroup {
                             windows: column.windows.clone(),
                             active: window,
                         },
-                        rect: Rect::new(rect.x, rect.y - header, rect.width, header),
+                        rect,
                     });
                 }
                 result.geometry.insert(window, rect);
@@ -2798,3 +2793,38 @@ mod tabbed_tests {
         }
     }
 }
+
+#[cfg(test)]
+mod overlay_tab_tests {
+    use super::*;
+
+    #[test]
+    fn tab_indicator_never_reserves_layout_space() {
+        let mut layout = ScrollingLayout::default();
+        let a = WindowId(1);
+        let b = WindowId(2);
+        layout.insert(a, None).unwrap();
+        layout.toggle_column_tabbed(a).unwrap();
+        let bounds = Rect::new(0., 0., 800., 600.);
+        let gaps = GapConfig {
+            inner: 12.,
+            outer: 8.,
+            smart: false,
+        };
+        let before = layout
+            .resolve_geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(a))
+            .unwrap();
+        layout.insert(b, Some(a)).unwrap();
+        layout.move_into_column(b, a).unwrap();
+        let after = layout
+            .resolve_geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(b))
+            .unwrap();
+        assert_eq!(before.geometry[&a], after.geometry[&b]);
+        assert_eq!(after.tab_bars[0].rect, after.geometry[&b]);
+        layout.focus_and_reveal(a).unwrap();
+        let switched = layout
+            .resolve_geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(a))
+            .unwrap();
+        assert_eq!(switched.geometry[&a], after.geometry[&b]);
+    }
+}

docs/configuration.md

@@ -559,12 +559,50 @@ column's width and scroll position. Vertical resizing is inactive in tabbed mode
 `join-tab` explicitly makes the destination column tabbed, including when joining
 two rows that already share a column.
 
-The tab bar shows window titles above the active window and reserves space
+Tree groups show a compact title bar above the active window. Scrolling columns
-inside its allocation. Click a title to switch. New windows open beside the
+use a segmented rail along the left edge. Click a segment to select its tab, or
-group. Closing, floating, or moving a tab to another workspace removes it from
+hover over the rail to open a title list. The list stays open while the pointer
-the group; a single remaining window loses its tab bar. Maximized and fullscreen
+is over the rail or list, and scrolls if it is taller than the screen. Keyboard
-windows hide the bar. Fullscreen remains per-window: restore before grouping or
+tab switching briefly shows `n/N · title` near the top of the window.
-switching tabs. Switching layout modes keeps every window but dissolves groups.
+
+The scrolling indicator and its title list are overlays: neither reserves space
+nor changes the window size. With at least 8px of gap to the left, the rail sits
+in that gap; otherwise it sits just inside the window's left edge. Its invisible
+click area is wider than the rail. On very short windows, the segments compress
+to stay within the visible window height.
+
+New windows open beside the group. Closing, floating, or moving a tab to another
+workspace removes it from the group. Single-window groups, maximized windows and
+fullscreen windows hide the tab controls. Fullscreen remains per-window: restore
+before grouping or switching tabs. Switching layout modes keeps every window but
+dissolves groups.
+
+Configure the scrolling indicator under `scrolling.tab-indicator`:
+
+```kdl
+scrolling {
+    tab-indicator {
+        width 4
+        segment-height 18
+        segment-gap 4
+        hit-width 12
+        gap-threshold 8
+        list-width 220
+        row-height 28
+        padding 4
+        font-size 12
+        flash-duration-ms 1000
+    }
+}
+```
+
+Sizes are logical pixels. `flash-duration-ms 0` disables keyboard feedback.
+Optional `active-color`, `inactive-color`, `background-color`, and `text-color`
+accept the same color syntax as theme colors. When omitted, they follow the
+current theme's accent, border, base surface, and primary text respectively.
+The rail has fully rounded ends; the title list follows the shell corner radius.
+Both use flat fills, without blur or shadows. Changes apply on configuration
+reload.
 
 To make future scrolling columns tabbed by default:
 

docs/shortcuts.md

@@ -178,3 +178,7 @@ binding "Super+Q" disabled=#true
 
 See [Commands and bindings](configuration.md#commands-and-bindings) for action
 names, arguments, and physical-key matching.
+
+In scrolling columns, hover over the left-edge tab indicator for window titles.
+Click a segment or title to switch tabs. Keyboard tab switching briefly shows the
+selected tab number and title without opening the list.

scripts/tests/test_tree_tabs_isolated.py

@@ -37,7 +37,8 @@ class TabGroupsTest(unittest.TestCase):
             runtime.mkdir(mode=0o700)
             config = root / "config/ferese"
             config.mkdir(parents=True)
-            (config / "config.kdl").write_text(f'layout {{ mode "{mode}"; }}\nanimations {{ enabled #false; }}\n')
+            (config / "config.kdl").write_text(f'layout {{ mode "{mode}"; }}\nanimations {{ enabled #false; }}\n'
+                + 'scrolling { tab-indicator { active-color "#ff0000"; inactive-color "#00ff00"; }; }\n')
             host = Path(os.environ["WAYLAND_DISPLAY"])
             if not host.is_absolute():
                 host = Path(os.environ["XDG_RUNTIME_DIR"]) / host
@@ -117,6 +118,20 @@ class TabGroupsTest(unittest.TestCase):
                         captured = subprocess.check_output([str(ctl), "screenshot"],
                                                            env=ipc_environment(env), stderr=log, timeout=10)
                         image = Image.open(io.BytesIO(captured)).convert("RGB")
+                        if mode == "scrolling":
+                            # The overlay rail sits inside the left edge at the default 4px gap.
+                            for index, window_id in enumerate(ids):
+                                x = round((active["x"] + 2) * scale)
+                                y = round((active["y"] + active["height"] / 2 + (index - 1) * 22) * scale)
+                                r, g, b = image.getpixel((x, y))
+                                if window_id == active["id"]:
+                                    if r < 180 or g > 60 or b > 60:
+                                        return False
+                                elif g < 180 or r > 60 or b > 60:
+                                    return False
+                            self.assertEqual(active["y"], current_neighbor["y"])
+                            self.assertEqual(active["height"], current_neighbor["height"])
+                            return True
                         for index in range(3):
                             left = active["x"] + active["width"] * index / 3 + 4
                             right = active["x"] + active["width"] * (index + 1) / 3 - 4