all: add support for hy3 like tiling

src/compositor.rs

@@ -62,6 +62,7 @@ use {
             WorkspaceDisplayOrder, WorkspaceNode, container_layout, container_render_positions,
             float_layout, output_render_data,
             placeholder_render_textures,
+            container_tab_render_textures,
         },
         user_session::import_environment,
         utils::{
@@ -265,6 +266,7 @@ fn start_compositor2(
         pending_toplevel_screencasts: Default::default(),
         pending_screencast_reallocs_or_reconfigures: Default::default(),
         pending_placeholder_render_textures: Default::default(),
+        pending_container_tab_render_textures: Default::default(),
         dbus: Dbus::new(&engine, &ring, &run_toplevel),
         fdcloser: FdCloser::new(),
         logger: logger.clone(),
@@ -514,6 +516,11 @@ fn start_global_event_handlers(state: &Rc<State>) -> Vec<SpawnedFuture<()>> {
             Phase::PostLayout,
             placeholder_render_textures(state.clone()),
         ),
+        eng.spawn2(
+            "container tab textures",
+            Phase::PostLayout,
+            container_tab_render_textures(state.clone()),
+        ),
         eng.spawn2(
             "output render",
             Phase::PostLayout,

src/config/handler.rs

@@ -1757,6 +1757,41 @@ impl ConfigProxyHandler {
         Ok(())
     }
 
+    fn handle_seat_toggle_tab(&self, seat: Seat) -> Result<(), CphError> {
+        let seat = self.get_seat(seat)?;
+        seat.toggle_tab();
+        Ok(())
+    }
+
+    fn handle_seat_make_group(
+        &self,
+        seat: Seat,
+        axis: Axis,
+        ephemeral: bool,
+    ) -> Result<(), CphError> {
+        let seat = self.get_seat(seat)?;
+        seat.make_group(axis.into(), ephemeral);
+        Ok(())
+    }
+
+    fn handle_seat_change_group_opposite(&self, seat: Seat) -> Result<(), CphError> {
+        let seat = self.get_seat(seat)?;
+        seat.change_group_opposite();
+        Ok(())
+    }
+
+    fn handle_seat_equalize(&self, seat: Seat, recursive: bool) -> Result<(), CphError> {
+        let seat = self.get_seat(seat)?;
+        seat.equalize(recursive);
+        Ok(())
+    }
+
+    fn handle_seat_move_tab(&self, seat: Seat, right: bool) -> Result<(), CphError> {
+        let seat = self.get_seat(seat)?;
+        seat.move_tab(right);
+        Ok(())
+    }
+
     fn handle_get_window_split(&self, window: Window) -> Result<(), CphError> {
         let window = self.get_window(window)?;
         self.respond(Response::GetWindowSplit {
@@ -2464,6 +2499,12 @@ impl ConfigProxyHandler {
             BAR_SEPARATOR_WIDTH => ThemeSized::bar_separator_width,
             GAP => ThemeSized::gap,
             TITLE_GAP => ThemeSized::title_gap,
+            TAB_BAR_HEIGHT => ThemeSized::tab_bar_height,
+            TAB_BAR_PADDING => ThemeSized::tab_bar_padding,
+            TAB_BAR_RADIUS => ThemeSized::tab_bar_radius,
+            TAB_BAR_BORDER_WIDTH => ThemeSized::tab_bar_border_width,
+            TAB_BAR_TEXT_PADDING => ThemeSized::tab_bar_text_padding,
+            TAB_BAR_GAP => ThemeSized::tab_bar_gap,
             _ => return Err(CphError::UnknownSized(sized.0)),
         };
         Ok(sized)
@@ -2541,6 +2582,14 @@ impl ConfigProxyHandler {
             BAR_STATUS_TEXT_COLOR => ThemeColor::bar_text,
             ATTENTION_REQUESTED_BACKGROUND_COLOR => ThemeColor::attention_requested_background,
             HIGHLIGHT_COLOR => ThemeColor::highlight,
+            TAB_ACTIVE_BACKGROUND_COLOR => ThemeColor::tab_active_background,
+            TAB_ACTIVE_BORDER_COLOR => ThemeColor::tab_active_border,
+            TAB_INACTIVE_BACKGROUND_COLOR => ThemeColor::tab_inactive_background,
+            TAB_INACTIVE_BORDER_COLOR => ThemeColor::tab_inactive_border,
+            TAB_ACTIVE_TEXT_COLOR => ThemeColor::tab_active_text,
+            TAB_INACTIVE_TEXT_COLOR => ThemeColor::tab_inactive_text,
+            TAB_BAR_BACKGROUND_COLOR => ThemeColor::tab_bar_background,
+            TAB_ATTENTION_BACKGROUND_COLOR => ThemeColor::tab_attention_background,
             _ => return Err(CphError::UnknownColor(colorable.0)),
         };
         Ok(colorable)
@@ -3448,6 +3497,40 @@ impl ConfigProxyHandler {
             } => self
                 .handle_window_resize(window, dx1, dy1, dx2, dy2)
                 .wrn("window_resize")?,
+            ClientMessage::SeatToggleTab { seat } => self
+                .handle_seat_toggle_tab(seat)
+                .wrn("seat_toggle_tab")?,
+            ClientMessage::SeatMakeGroup {
+                seat,
+                axis,
+                ephemeral,
+            } => self
+                .handle_seat_make_group(seat, axis, ephemeral)
+                .wrn("seat_make_group")?,
+            ClientMessage::SeatChangeGroupOpposite { seat } => self
+                .handle_seat_change_group_opposite(seat)
+                .wrn("seat_change_group_opposite")?,
+            ClientMessage::SeatEqualize { seat, recursive } => self
+                .handle_seat_equalize(seat, recursive)
+                .wrn("seat_equalize")?,
+            ClientMessage::SetAutotile { enabled } => {
+                self.state.theme.autotile_enabled.set(enabled);
+            }
+            ClientMessage::SeatToggleExpand { .. } => {
+                // Removed feature; kept for binary protocol compatibility.
+            }
+            ClientMessage::SetTabTitleAlign { align } => {
+                use crate::theme::TabTitleAlign;
+                let val = match align {
+                    1 => TabTitleAlign::Center,
+                    2 => TabTitleAlign::End,
+                    _ => TabTitleAlign::Start,
+                };
+                self.state.theme.tab_title_align.set(val);
+            }
+            ClientMessage::SeatMoveTab { seat, right } => self
+                .handle_seat_move_tab(seat, right)
+                .wrn("seat_move_tab")?,
         }
         Ok(())
     }

src/gfx_api.rs

@@ -306,6 +306,8 @@ pub struct RoundedFillRect {
     pub border_width: f32,
     /// Output scale for antialiasing.
     pub scale: f32,
+    /// Sort order hint within the RoundedFill bucket (lower renders first).
+    pub z_order: u32,
 }
 
 impl RoundedFillRect {

src/gfx_apis/vulkan/renderer.rs

@@ -254,6 +254,7 @@ struct VulkanRoundedFillOp {
     border_width: f32,
     scale: f32,
     range_address: DeviceAddress,
+    z_order: u32,
 }
 
 struct VulkanRoundedTexOp {
@@ -923,7 +924,7 @@ impl VulkanRenderer {
                     enum Key {
                         Fill { color: [u32; 4] },
                         Tex(usize),
-                        RoundedFill { color: [u32; 4] },
+                        RoundedFill { z_order: u32, color: [u32; 4] },
                         RoundedTex(usize),
                     }
                     match o {
@@ -932,6 +933,7 @@ impl VulkanRenderer {
                         },
                         VulkanOp::Tex(t) => Key::Tex(t.index),
                         VulkanOp::RoundedFill(f) => Key::RoundedFill {
+                            z_order: f.z_order,
                             color: f.color.map(|c| c.to_bits()),
                         },
                         VulkanOp::RoundedTex(t) => Key::RoundedTex(t.index),
@@ -1152,6 +1154,7 @@ impl VulkanRenderer {
                             border_width: rf.border_width,
                             scale: rf.scale,
                             range_address: 0,
+                            z_order: rf.z_order,
                         }));
                     }
                 }
@@ -2385,12 +2388,13 @@ impl VulkanRenderer {
                     };
                     (opaque, c.target)
                 }
-                GfxApiOpt::RoundedFillRect(_) => {
-                    // Rounded rects are never fully opaque due to AA at corners
-                    continue;
+                GfxApiOpt::RoundedFillRect(rf) => {
+                    // Rounded rects are never fully opaque due to AA at corners,
+                    // but they do paint pixels and need paint regions.
+                    (false, rf.rect)
                 }
-                GfxApiOpt::RoundedCopyTexture(_) => {
-                    continue;
+                GfxApiOpt::RoundedCopyTexture(ct) => {
+                    (false, ct.target)
                 }
             };
             if opaque || bb.is_none() {

src/ifs/wl_seat.rs

@@ -83,7 +83,7 @@ use {
         rect::Rect,
         state::{DeviceHandlerData, State},
         tree::{
-            ContainerNode, ContainerSplit, Direction, FoundNode, Node, NodeId, NodeLayer,
+            ContainerNode, ContainerSplit, ChangeGroupAction, Direction, FoundNode, Node, NodeId, NodeLayer,
             NodeLayerLink, NodeLocation, OutputNode, StackedNode, ToplevelNode, WorkspaceNode,
             generic_node_visitor, toplevel_create_split, toplevel_parent_container,
             toplevel_set_floating, toplevel_set_workspace,
@@ -745,6 +745,40 @@ impl WlSeatGlobal {
         toplevel_create_split(&self.state, tl, axis);
     }
 
+    pub fn toggle_tab(&self) {
+        if let Some(c) = self.kb_parent_container() {
+            c.change_group(ChangeGroupAction::ToggleTab);
+        }
+    }
+
+    pub fn make_group(&self, axis: ContainerSplit, ephemeral: bool) {
+        if let Some(c) = self.kb_parent_container() {
+            c.make_group(axis, ephemeral);
+        }
+    }
+
+    pub fn change_group_opposite(&self) {
+        if let Some(c) = self.kb_parent_container() {
+            c.change_group(ChangeGroupAction::Opposite);
+        }
+    }
+
+    pub fn equalize(&self, recursive: bool) {
+        if let Some(c) = self.kb_parent_container() {
+            if recursive {
+                c.equalize_recursive();
+            } else {
+                c.equalize();
+            }
+        }
+    }
+
+    pub fn move_tab(&self, right: bool) {
+        if let Some(c) = self.kb_parent_container() {
+            c.move_tab(right);
+        }
+    }
+
     pub fn focus_parent(self: &Rc<Self>) {
         if let Some(tl) = self.keyboard_node.get().node_toplevel()
             && let Some(parent) = tl.tl_data().parent.get()

src/renderer.rs

@@ -15,7 +15,7 @@ use {
         theme::{Color, CornerRadius},
         tree::{
             ContainerNode, DisplayNode, FloatNode, OutputNode, PlaceholderNode, ToplevelData,
-            ToplevelNodeBase, WorkspaceNode,
+            ToplevelNodeBase, WorkspaceNode, tab_bar::TabBar,
         },
     },
     std::{ops::Deref, rc::Rc, slice},
@@ -277,6 +277,105 @@ impl Renderer<'_> {
         self.render_tl_aux(placeholder.tl_data(), bounds, true);
     }
 
+    fn render_tab_bar(&mut self, tab_bar: &TabBar, x: i32, y: i32, _container_width: i32) {
+        let srgb_srgb = self.state.color_manager.srgb_gamma22();
+        let srgb = &srgb_srgb.linear;
+        let perceptual = RenderIntent::Perceptual;
+        let scalef = self.base.scalef as f32;
+
+        let radius = self.state.theme.sizes.tab_bar_radius.get();
+        let border_width = self.state.theme.sizes.tab_bar_border_width.get();
+        let text_padding = self.state.theme.sizes.tab_bar_text_padding.get();
+        let bar_height = tab_bar.height;
+        let render_scale = tab_bar.render_scale;
+
+        // Vulkan sorts ops: Fill < Tex < RoundedFill (by z_order, color) < RoundedTex.
+        // We use:
+        //   FillRect           – tiny strip for Vulkan paint regions (hidden)
+        //   RoundedFillRect z0 – solid rounded bg
+        //   RoundedFillRect z1 – rounded border ring (on top of bg)
+        //   RoundedCopyTexture – title text (on top of everything)
+        for entry in &tab_bar.entries {
+            let (bg_color, border_color, _text_color) =
+                TabBar::entry_colors(self.state, entry);
+            let ex = entry.x.get();
+            let ew = entry.width.get();
+            let tab_rect = Rect::new_sized_saturating(ex, 0, ew, bar_height);
+            let tab_cr = CornerRadius::from(radius as f32);
+
+            // Tiny FillRect strip to establish Vulkan paint regions (visually hidden
+            // behind the RoundedFillRect bg that renders later).
+            let strip = Rect::new_sized_saturating(ex + radius, bar_height / 2, (ew - 2 * radius).max(1), 1);
+            self.base
+                .fill_boxes2(slice::from_ref(&strip), &bg_color, srgb, perceptual, x, y);
+
+            // Rounded solid bg fill (z_order=0, renders first among RoundedFill).
+            self.base.fill_rounded_rect_z(
+                tab_rect.move_(x, y),
+                &bg_color,
+                None,
+                srgb,
+                perceptual,
+                tab_cr.scaled_by(scalef),
+                0.0,
+                0,
+            );
+
+            // Rounded border ring on top (z_order=1, renders after bg).
+            if border_width > 0 {
+                self.base.fill_rounded_rect_z(
+                    tab_rect.move_(x, y),
+                    &border_color,
+                    None,
+                    srgb,
+                    perceptual,
+                    tab_cr.scaled_by(scalef),
+                    border_width as f32 * scalef,
+                    1,
+                );
+            }
+
+            // Title text as RoundedCopyTexture (sorts after all RoundedFill).
+            let tex_ref = entry.title_texture.borrow();
+            if let Some(tex) = tex_ref.as_ref()
+                && let Some(texture) = tex.texture()
+            {
+                use crate::theme::TabTitleAlign;
+                let (tw, _th) = texture.size();
+                let tex_width = (tw as f64 / render_scale.to_f64()).round() as i32;
+                let tab_inner = ew - 2 * (text_padding + border_width);
+                let text_x = match self.state.theme.tab_title_align.get() {
+                    TabTitleAlign::Start => x + ex + text_padding + border_width,
+                    TabTitleAlign::Center => {
+                        x + ex + border_width + (tab_inner.max(0) - tex_width).max(0) / 2 + text_padding.min(tab_inner.max(0) / 2)
+                    }
+                    TabTitleAlign::End => {
+                        let end_x = x + ex + ew - tex_width - text_padding - border_width;
+                        end_x.max(x + ex + border_width)
+                    }
+                };
+                let (tx, ty) = self.base.scale_point(text_x, y);
+                self.base.render_rounded_texture(
+                    &texture,
+                    None,
+                    tx,
+                    ty,
+                    None,
+                    None,
+                    render_scale,
+                    None,
+                    None,
+                    AcquireSync::None,
+                    ReleaseSync::None,
+                    self.state.color_manager.srgb_gamma22(),
+                    perceptual,
+                    AlphaMode::PremultipliedElectrical,
+                    CornerRadius::from(0.0_f32),
+                );
+            }
+        }
+    }
+
     fn render_container_decorations(&mut self, container: &ContainerNode, x: i32, y: i32) {
         let srgb_srgb = self.state.color_manager.srgb_gamma22();
         let srgb = &srgb_srgb.linear;
@@ -291,6 +390,13 @@ impl Renderer<'_> {
         self.render_container_decorations(container, x, y);
 
         if let Some(child) = container.mono_child.get() {
+            // Render tab bar if present.
+            {
+                let tab_bar = container.tab_bar.borrow();
+                if let Some(tb) = tab_bar.as_ref() {
+                    self.render_tab_bar(tb, x, y, container.width.get());
+                }
+            }
             let mb = container.mono_body.get();
             if self.state.theme.sizes.gap.get() != 0 {
                 let srgb_srgb = self.state.color_manager.srgb_gamma22();
@@ -308,21 +414,22 @@ impl Renderer<'_> {
                 let perceptual = RenderIntent::Perceptual;
                 if !child.node.node_is_container() {
                     let cr = self.state.theme.corner_radius.get();
-                    let full_h = mb.y2();
+                    let frame_y = mb.y1();
+                    let frame_h = mb.height();
                     if cr.is_zero() {
                         let frame_rects = [
-                            Rect::new_sized_saturating(mb.x1() - bw, 0, bw, full_h),
-                            Rect::new_sized_saturating(mb.x2(), 0, bw, full_h),
-                            Rect::new_sized_saturating(mb.x1() - bw, -bw, full_w + 2 * bw, bw),
-                            Rect::new_sized_saturating(mb.x1() - bw, full_h, full_w + 2 * bw, bw),
+                            Rect::new_sized_saturating(mb.x1() - bw, frame_y, bw, frame_h),
+                            Rect::new_sized_saturating(mb.x2(), frame_y, bw, frame_h),
+                            Rect::new_sized_saturating(mb.x1() - bw, frame_y - bw, full_w + 2 * bw, bw),
+                            Rect::new_sized_saturating(mb.x1() - bw, frame_y + frame_h, full_w + 2 * bw, bw),
                         ];
                         self.base.fill_boxes2(&frame_rects, c, srgb, perceptual, x, y);
                     } else {
                         let outer = Rect::new_sized_saturating(
                             mb.x1() - bw,
-                            -bw,
+                            frame_y - bw,
                             full_w + 2 * bw,
-                            full_h + 2 * bw,
+                            frame_h + 2 * bw,
                         );
                         let scalef = self.base.scalef as f32;
                         let scaled_cr = cr.scaled_by(scalef);

src/renderer/renderer_base.rs

@@ -259,6 +259,20 @@ impl RendererBase<'_> {
         render_intent: RenderIntent,
         corner_radius: CornerRadius,
         border_width: f32,
+    ) {
+        self.fill_rounded_rect_z(rect, color, alpha, cd, render_intent, corner_radius, border_width, 0)
+    }
+
+    pub fn fill_rounded_rect_z(
+        &mut self,
+        rect: Rect,
+        color: &Color,
+        alpha: Option<f32>,
+        cd: &Rc<LinearColorDescription>,
+        render_intent: RenderIntent,
+        corner_radius: CornerRadius,
+        border_width: f32,
+        z_order: u32,
     ) {
         if *color == Color::TRANSPARENT {
             return;
@@ -288,6 +302,7 @@ impl RendererBase<'_> {
                 corner_radius: cr,
                 border_width,
                 scale,
+                z_order,
             }));
     }
 

src/state.rs

@@ -195,6 +195,7 @@ pub struct State {
     pub pending_toplevel_screencasts: AsyncQueue<Rc<JayScreencast>>,
     pub pending_screencast_reallocs_or_reconfigures: AsyncQueue<Rc<JayScreencast>>,
     pub pending_placeholder_render_textures: AsyncQueue<Rc<PlaceholderNode>>,
+    pub pending_container_tab_render_textures: AsyncQueue<Rc<ContainerNode>>,
     pub dbus: Dbus,
     pub fdcloser: Arc<FdCloser>,
     pub logger: Option<Arc<Logger>>,
@@ -1112,6 +1113,7 @@ impl State {
         self.pending_toplevel_screencasts.clear();
         self.pending_screencast_reallocs_or_reconfigures.clear();
         self.pending_placeholder_render_textures.clear();
+        self.pending_container_tab_render_textures.clear();
         self.render_ctx_watchers.clear();
         self.workspace_watchers.clear();
         self.toplevel_lists.clear();

src/theme.rs

@@ -454,6 +454,14 @@ colors! {
     bar_text = (0xff, 0xff, 0xff),
     attention_requested_background = (0x23, 0x09, 0x2c),
     highlight = (0x9d, 0x28, 0xc6, 0x7f),
+    tab_active_background = (0x4c, 0x78, 0x99),
+    tab_active_border = (0x28, 0x55, 0x77),
+    tab_inactive_background = (0x22, 0x22, 0x22),
+    tab_inactive_border = (0x33, 0x33, 0x33),
+    tab_active_text = (0xff, 0xff, 0xff),
+    tab_inactive_text = (0x88, 0x88, 0x88),
+    tab_bar_background = (0x00, 0x00, 0x00, 0x00),
+    tab_attention_background = (0x23, 0x09, 0x2c),
 }
 
 impl StaticText for ThemeColor {
@@ -476,6 +484,14 @@ impl StaticText for ThemeColor {
             ThemeColor::bar_text => "Bar Text",
             ThemeColor::attention_requested_background => "Attention Requested",
             ThemeColor::highlight => "Highlight",
+            ThemeColor::tab_active_background => "Tab Background (active)",
+            ThemeColor::tab_active_border => "Tab Border (active)",
+            ThemeColor::tab_inactive_background => "Tab Background (inactive)",
+            ThemeColor::tab_inactive_border => "Tab Border (inactive)",
+            ThemeColor::tab_active_text => "Tab Text (active)",
+            ThemeColor::tab_inactive_text => "Tab Text (inactive)",
+            ThemeColor::tab_bar_background => "Tab Bar Background",
+            ThemeColor::tab_attention_background => "Tab Attention Background",
         }
     }
 }
@@ -588,6 +604,12 @@ sizes! {
     bar_separator_width = (0, 1000, 1),
     gap = (0, 1000, 0),
     title_gap = (0, 1000, 5),
+    tab_bar_height = (0, 1000, 22),
+    tab_bar_padding = (0, 1000, 6),
+    tab_bar_radius = (0, 1000, 6),
+    tab_bar_border_width = (0, 1000, 2),
+    tab_bar_text_padding = (0, 1000, 4),
+    tab_bar_gap = (0, 1000, 4),
 }
 
 impl StaticText for ThemeSized {
@@ -599,6 +621,12 @@ impl StaticText for ThemeSized {
             ThemeSized::bar_separator_width => "Bar Separator Width",
             ThemeSized::gap => "Gap",
             ThemeSized::title_gap => "Title Gap",
+            ThemeSized::tab_bar_height => "Tab Bar Height",
+            ThemeSized::tab_bar_padding => "Tab Bar Padding",
+            ThemeSized::tab_bar_radius => "Tab Bar Radius",
+            ThemeSized::tab_bar_border_width => "Tab Bar Border Width",
+            ThemeSized::tab_bar_text_padding => "Tab Bar Text Padding",
+            ThemeSized::tab_bar_gap => "Tab Bar Gap",
         }
     }
 }
@@ -732,6 +760,15 @@ impl CornerRadius {
     }
 }
 
+/// Horizontal alignment of title text inside tab buttons.
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
+pub enum TabTitleAlign {
+    #[default]
+    Start,
+    Center,
+    End,
+}
+
 pub struct Theme {
     pub colors: ThemeColors,
     pub sizes: ThemeSizes,
@@ -745,6 +782,8 @@ pub struct Theme {
     pub floating_titles: Cell<bool>,
     pub bar_position: Cell<BarPosition>,
     pub corner_radius: Cell<CornerRadius>,
+    pub autotile_enabled: Cell<bool>,
+    pub tab_title_align: Cell<TabTitleAlign>,
 }
 
 impl Default for Theme {
@@ -761,6 +800,8 @@ impl Default for Theme {
             floating_titles: Cell::new(false),
             bar_position: Default::default(),
             corner_radius: Cell::new(CornerRadius::default()),
+            autotile_enabled: Cell::new(false),
+            tab_title_align: Cell::new(TabTitleAlign::default()),
         }
     }
 }
@@ -770,6 +811,10 @@ impl Theme {
         self.bar_font.get().unwrap_or_else(|| self.font.get())
     }
 
+    pub fn title_font(&self) -> Arc<String> {
+        self.title_font.get().unwrap_or_else(|| self.font.get())
+    }
+
     pub fn title_height(&self) -> i32 {
         0
     }

src/tree.rs

@@ -50,6 +50,7 @@ mod float;
 mod output;
 mod placeholder;
 mod stacked;
+pub mod tab_bar;
 mod toplevel;
 mod walker;
 mod workspace;

src/tree/container.rs

@@ -12,20 +12,24 @@ use {
         },
         rect::Rect,
         renderer::Renderer,
+        scale::Scale,
         state::State,
+        text::TextTexture,
         tree::{
             ContainingNode, Direction, FindTreeResult, FindTreeUsecase, FloatNode, FoundNode, Node,
             NodeId, NodeLayerLink, NodeLocation, OutputNode, TddType, TileDragDestination,
             ToplevelData, ToplevelNode, ToplevelNodeBase, ToplevelType, WorkspaceNode,
-            default_tile_drag_bounds, toplevel_set_workspace,
+            default_tile_drag_bounds, tab_bar::{TabBar, TabBarEntry}, toplevel_set_workspace,
             walker::NodeVisitor,
         },
         utils::{
             clonecell::CloneCell,
+            errorfmt::ErrorFmt,
             event_listener::LazyEventSource,
             hash_map_ext::HashMapExt,
             linkedlist::{LinkedList, LinkedNode, NodeRef},
             numcell::NumCell,
+            on_drop_event::OnDropEvent,
             rc_eq::rc_eq,
             threshold_counter::ThresholdCounter,
         },
@@ -85,6 +89,28 @@ pub enum ContainerFocus {
 
 tree_id!(ContainerNodeId);
 
+/// Ephemeral group state (hy3-style auto-collapse).
+///
+/// An ephemeral container is a transient grouping that auto-collapses back to
+/// its single child when all but one child is removed.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
+pub enum Ephemeral {
+    /// Normal container — never auto-collapses.
+    #[default]
+    Off,
+    /// Ephemeral container — when child count drops to 1, collapse.
+    On,
+}
+
+/// Actions for the `changegroup` operation.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum ChangeGroupAction {
+    /// Toggle between Horizontal and Vertical.
+    Opposite,
+    /// Toggle between tabbed (mono) and split mode.
+    ToggleTab,
+}
+
 #[derive(Default)]
 pub struct ContainerRenderData {
     pub border_rects: Vec<Rect>,
@@ -120,6 +146,9 @@ pub struct ContainerNode {
     pub child_added: Rc<LazyEventSource>,
     pub child_removed: Rc<LazyEventSource>,
     pub all_children_resized: Rc<LazyEventSource>,
+    pub tab_bar: RefCell<Option<TabBar>>,
+    pub update_tab_textures_scheduled: Cell<bool>,
+    pub ephemeral: Cell<Ephemeral>,
 }
 
 impl Debug for ContainerNode {
@@ -231,6 +260,9 @@ impl ContainerNode {
             child_added: state.lazy_event_sources.create_source(),
             child_removed: state.lazy_event_sources.create_source(),
             all_children_resized: state.post_layout_event_sources.create_source(),
+            tab_bar: RefCell::new(None),
+            update_tab_textures_scheduled: Cell::new(false),
+            ephemeral: Cell::new(Ephemeral::Off),
         });
         child.tl_set_parent(slf.clone());
         slf.pull_child_properties(&child_node_ref);
@@ -335,6 +367,8 @@ impl ContainerNode {
         self.sum_factors.set(sum_factors);
         if self.mono_child.is_some() {
             self.activate_child(&new_ref);
+            self.rebuild_tab_bar();
+            self.damage();
         }
         // log::info!("add_child");
         self.schedule_layout();
@@ -549,11 +583,19 @@ impl ContainerNode {
                 self.content_width.set(self.width.get());
             }
         }
+        let tab_bar_height = if self.mono_child.is_some() {
+            // Tab bar sits above the window with a configurable gap.
+            let tbh = self.state.theme.sizes.tab_bar_height.get();
+            let gap = self.state.theme.sizes.tab_bar_gap.get();
+            tbh + gap
+        } else {
+            0
+        };
         self.mono_body.set(Rect::new_sized_saturating(
             0,
-            0,
+            tab_bar_height,
             self.width.get(),
-            self.height.get(),
+            (self.height.get() - tab_bar_height).max(0),
         ));
     }
 
@@ -588,7 +630,9 @@ impl ContainerNode {
                     dist_left,
                     dist_right,
                 } => {
-                    let prev = op.child.prev().unwrap();
+                    let Some(prev) = op.child.prev() else {
+                        return;
+                    };
                     let prev_body = prev.body.get();
                     let child_body = op.child.body.get();
                     let (prev_factor, child_factor) = match self.split.get() {
@@ -656,6 +700,14 @@ impl ContainerNode {
         }
     }
 
+    fn schedule_update_tab_textures(self: &Rc<Self>) {
+        if !self.update_tab_textures_scheduled.replace(true) {
+            self.state
+                .pending_container_tab_render_textures
+                .push(self.clone());
+        }
+    }
+
     fn compute_render_positions(&self) {
         self.compute_render_positions_scheduled.set(false);
         let mut rd = self.render_data.borrow_mut();
@@ -713,6 +765,13 @@ impl ContainerNode {
                 }
             }
             self.mono_child.set(Some(child.clone()));
+            // Keep focus_history in sync with mono_child so that
+            // toggle_tab and other operations that use focus_history.last()
+            // return the correct child.
+            child
+                .focus_history
+                .set(Some(self.focus_history.add_last(child.clone())));
+            self.rebuild_tab_bar();
             if self.toplevel_data.visible.get() {
                 self.perform_layout();
                 child.node.tl_set_visible(true);
@@ -764,9 +823,25 @@ impl ContainerNode {
                 }
             }
         }
-        self.mono_child.set(child);
-        // log::info!("set_mono");
+        self.mono_child.set(child.clone());
+        if child.is_some() {
+            self.rebuild_tab_bar();
+        } else {
+            *self.tab_bar.borrow_mut() = None;
+        }
+        self.update_content_size();
+        self.damage();
         self.schedule_layout();
+        // Notify parent to rebuild its tab bar if we're a child of a mono container.
+        // Our tab title prefix changes when we enter/leave mono mode ([T] vs [H]/[V]).
+        if let Some(parent) = self.toplevel_data.parent.get() {
+            if let Some(pc) = parent.node_into_container() {
+                if pc.mono_child.is_some() {
+                    pc.rebuild_tab_bar();
+                    pc.damage();
+                }
+            }
+        }
     }
 
     pub fn set_split(self: &Rc<Self>, split: ContainerSplit) {
@@ -777,6 +852,233 @@ impl ContainerNode {
         }
     }
 
+    /// Rebuild the tab bar entries from the current children.
+    ///
+    /// Called when entering mono mode or when children change while in mono mode.
+    fn rebuild_tab_bar(self: &Rc<Self>) {
+        self.rebuild_tab_bar_with_override(None, None);
+    }
+
+    /// Generate a tab title for a child node. For windows this is the window
+    /// title or app_id. For container (group) children, we show a layout
+    /// prefix like hy3: `[H] child_title`, `[V] child_title`, `[T] child_title`.
+    fn get_child_tab_title(
+        &self,
+        child: &ContainerChild,
+        override_id: Option<NodeId>,
+        override_title: Option<&str>,
+    ) -> String {
+        let child_id = child.node.node_id();
+        // If this child is a container (group), show layout prefix + focused child title.
+        if let Some(cn) = child.node.clone().node_into_container() {
+            let prefix = if cn.mono_child.is_some() {
+                "[T]"
+            } else {
+                match cn.split.get() {
+                    ContainerSplit::Horizontal => "[H]",
+                    ContainerSplit::Vertical => "[V]",
+                }
+            };
+            // Get the focused child's title recursively.
+            let inner = if let Some(focused) = cn.focus_history.last() {
+                let inner_child = ContainerChild {
+                    node: focused.node.clone(),
+                    active: Cell::new(false),
+                    body: Default::default(),
+                    content: Default::default(),
+                    factor: Cell::new(0.0),
+                    focus_history: Default::default(),
+                    attention_requested: Cell::new(false),
+                    border_color_is_focused: Default::default(),
+                };
+                cn.get_child_tab_title(&inner_child, override_id, override_title)
+            } else {
+                "Group".to_string()
+            };
+            return format!("{} {}", prefix, inner);
+        }
+        // Window node: use override, title, app_id, or "untitled".
+        let raw_title = if override_id == Some(child_id) && override_title.is_some() {
+            override_title.unwrap().to_string()
+        } else {
+            child.node.tl_data().title.borrow().clone()
+        };
+        if !raw_title.is_empty() {
+            return raw_title;
+        }
+        if override_id == Some(child_id) {
+            let app = child.node.tl_data().app_id.borrow().clone();
+            if !app.is_empty() {
+                return app;
+            }
+        } else {
+            let app = child.node.tl_data().app_id.borrow().clone();
+            if !app.is_empty() {
+                return app;
+            }
+        }
+        "untitled".to_string()
+    }
+
+    /// Rebuild the tab bar. If `override_id` and `override_title` are provided,
+    /// use the override title for that child instead of borrowing it (avoids
+    /// RefCell double-borrow when called from node_child_title_changed).
+    fn rebuild_tab_bar_with_override(
+        self: &Rc<Self>,
+        override_id: Option<NodeId>,
+        override_title: Option<&str>,
+    ) {
+        let mono = self.mono_child.get();
+        if mono.is_none() {
+            *self.tab_bar.borrow_mut() = None;
+            return;
+        }
+        let mono_ref = mono.as_ref().unwrap();
+        let active_id = mono_ref.node.node_id();
+        let height = self.state.theme.sizes.tab_bar_height.get();
+        let render_scale = self.workspace.get().output.get().global.persistent.scale.get();
+        let mut bar = TabBar::new(height, render_scale);
+        for child in self.children.iter() {
+            let child_id = child.node.node_id();
+            let title = self.get_child_tab_title(&child, override_id, override_title);
+            bar.entries.push(TabBarEntry {
+                child_id,
+                title,
+                title_texture: Rc::new(RefCell::new(None)),
+                active: child_id == active_id,
+                attention_requested: child.attention_requested.get(),
+                x: Cell::new(0),
+                width: Cell::new(0),
+            });
+        }
+        let padding = self.state.theme.sizes.tab_bar_padding.get();
+        bar.layout_entries(self.width.get(), padding);
+        *self.tab_bar.borrow_mut() = Some(bar);
+        self.schedule_update_tab_textures();
+    }
+
+    /// Wrap the focused child in a new sub-container with the given split direction.
+    ///
+    /// This is hy3's `makegroup` operation.
+    pub fn make_group(self: &Rc<Self>, split: ContainerSplit, ephemeral: bool) {
+        let Some(focused) = self.focus_history.last() else {
+            return;
+        };
+        if self.num_children.get() <= 1 {
+            return;
+        }
+        let focused_node = focused.node.clone();
+        // Record the sibling that comes AFTER the focused child so we can
+        // insert the new group at the same position.
+        let next_sibling: Option<Rc<dyn ToplevelNode>> = {
+            let nodes = self.child_nodes.borrow();
+            nodes
+                .get(&focused_node.node_id())
+                .and_then(|ln| ln.next())
+                .map(|n| n.node.clone())
+        };
+        // Temporarily disable ephemeral collapse during make_group so
+        // removing the focused child doesn't destroy this container.
+        let was_ephemeral = self.ephemeral.replace(Ephemeral::Off);
+        self.clone().cnode_remove_child2(&*focused_node, true);
+        self.ephemeral.set(was_ephemeral);
+        let sub = ContainerNode::new(
+            &self.state,
+            &self.workspace.get(),
+            focused_node,
+            split,
+        );
+        if ephemeral {
+            sub.ephemeral.set(Ephemeral::On);
+        }
+        // Insert at the original position instead of appending to the end.
+        if let Some(ref next) = next_sibling {
+            self.add_child_before(&**next, sub);
+        } else {
+            // Was the last child — append.
+            self.append_child(sub);
+        }
+    }
+
+    /// Change this container's split direction (hy3's `changegroup`).
+    ///
+    /// `opposite` toggles H↔V, `toggletab` toggles between mono and split.
+    pub fn change_group(self: &Rc<Self>, action: ChangeGroupAction) {
+        match action {
+            ChangeGroupAction::Opposite => {
+                let new_split = match self.split.get() {
+                    ContainerSplit::Horizontal => ContainerSplit::Vertical,
+                    ContainerSplit::Vertical => ContainerSplit::Horizontal,
+                };
+                self.set_split(new_split);
+            }
+            ChangeGroupAction::ToggleTab => {
+                if self.mono_child.is_some() {
+                    // Exit mono/tabbed mode.
+                    self.set_mono(None);
+                } else if let Some(focused) = self.focus_history.last() {
+                    // Enter mono/tabbed mode with the focused child.
+                    self.set_mono(Some(&*focused.node));
+                }
+            }
+        }
+    }
+
+    /// Reset all children's factors to equal (hy3's `equalize`).
+    pub fn equalize(self: &Rc<Self>) {
+        let n = self.num_children.get();
+        if n == 0 {
+            return;
+        }
+        let factor = 1.0 / n as f64;
+        let mut sum = 0.0;
+        for child in self.children.iter() {
+            child.factor.set(factor);
+            sum += factor;
+        }
+        self.sum_factors.set(sum);
+        self.schedule_layout();
+    }
+
+    /// Recursively equalize all descendant containers.
+    pub fn equalize_recursive(self: &Rc<Self>) {
+        self.equalize();
+        for child in self.children.iter() {
+            if let Some(cn) = child.node.clone().node_into_container() {
+                cn.equalize_recursive();
+            }
+        }
+    }
+
+    /// Move the currently active tab left or right within the tab bar.
+    ///
+    /// This is the equivalent of hy3's `movewindow` within a tabbed group.
+    pub fn move_tab(self: &Rc<Self>, right: bool) {
+        let mc = match self.mono_child.get() {
+            Some(mc) => mc,
+            None => return,
+        };
+        let child_nodes = self.child_nodes.borrow();
+        let Some(link) = child_nodes.get(&mc.node.node_id()) else {
+            return;
+        };
+        let active_ref = link.to_ref();
+        if right {
+            if let Some(next) = active_ref.next() {
+                // Move active tab after the next sibling (moves right).
+                next.append_existing(&active_ref);
+            }
+        } else {
+            if let Some(prev) = active_ref.prev() {
+                // Move active tab before the previous sibling (moves left).
+                prev.prepend_existing(&active_ref);
+            }
+        }
+        drop(child_nodes);
+        self.rebuild_tab_bar();
+        self.damage();
+    }
+
     fn parent_container(&self) -> Option<Rc<ContainerNode>> {
         self.toplevel_data
             .parent
@@ -955,6 +1257,42 @@ impl ContainerNode {
     }
 
     pub fn insert_child(self: &Rc<Self>, node: Rc<dyn ToplevelNode>, direction: Direction) {
+        // Autotile: if the container would become too narrow/tall, wrap the
+        // focused child and new node in a perpendicular sub-container.
+        if self.state.theme.autotile_enabled.get() && self.mono_child.is_none() {
+            let (pw, ph) = self.predict_child_body_size();
+            let opposite = match self.split.get() {
+                ContainerSplit::Horizontal if pw > 0 && ph > 0 && pw < ph => {
+                    Some(ContainerSplit::Vertical)
+                }
+                ContainerSplit::Vertical if pw > 0 && ph > 0 && ph < pw => {
+                    Some(ContainerSplit::Horizontal)
+                }
+                _ => None,
+            };
+            if let Some(opp_split) = opposite {
+                if let Some(focused) = self.focus_history.last() {
+                    if self.num_children.get() <= 1 {
+                        // Single child, autotile not applicable.
+                    } else {
+                        let focused_node = focused.node.clone();
+                        let was_ephemeral = self.ephemeral.replace(Ephemeral::Off);
+                        self.clone().cnode_remove_child2(&*focused_node, true);
+                        self.ephemeral.set(was_ephemeral);
+                        let sub = ContainerNode::new(
+                            &self.state,
+                            &self.workspace.get(),
+                            focused_node,
+                            opp_split,
+                        );
+                        sub.ephemeral.set(Ephemeral::On);
+                        sub.append_child(node);
+                        self.append_child(sub);
+                        return;
+                    }
+                }
+            }
+        }
         let (split, right) = direction_to_split(direction);
         if split != self.split.get() || right {
             self.append_child(node);
@@ -1050,16 +1388,39 @@ impl ContainerNode {
             if !pressed {
                 return;
             }
+            // Handle tab bar clicks in mono mode.
+            if self.mono_child.is_some() {
+                let tab_bar = self.tab_bar.borrow();
+                if let Some(tb) = tab_bar.as_ref() {
+                    if seat_data.y >= 0 && seat_data.y < tb.height {
+                        if let Some(idx) = tb.entry_at_x(seat_data.x) {
+                            let child_id = tb.entries[idx].child_id;
+                            drop(tab_bar);
+                            drop(seat_datas);
+                            let children = self.child_nodes.borrow();
+                            if let Some(child) = children.get(&child_id) {
+                                let child_ref = child.to_ref();
+                                drop(children);
+                                self.activate_child(&child_ref);
+                            }
+                            return;
+                        }
+                    }
+                }
+            }
             let (kind, child) = 'res: {
                 let mono = self.mono_child.is_some();
                 for child in self.children.iter() {
                     if !mono {
                         if self.split.get() == ContainerSplit::Horizontal {
                             if seat_data.x < child.body.get().x1() {
+                                let Some(prev) = child.prev() else {
+                                    continue;
+                                };
                                 break 'res (
                                     SeatOpKind::Resize {
                                         dist_left: seat_data.x
-                                            - child.prev().unwrap().body.get().x2(),
+                                            - prev.body.get().x2(),
                                         dist_right: child.body.get().x1() - seat_data.x,
                                     },
                                     child,
@@ -1067,10 +1428,13 @@ impl ContainerNode {
                             }
                         } else {
                             if seat_data.y < child.body.get().y1() {
+                                let Some(prev) = child.prev() else {
+                                    continue;
+                                };
                                 break 'res (
                                     SeatOpKind::Resize {
                                         dist_left: seat_data.y
-                                            - child.prev().unwrap().body.get().y2(),
+                                            - prev.body.get().y2(),
                                         dist_right: child.body.get().y1() - seat_data.y,
                                     },
                                     child,
@@ -1285,6 +1649,78 @@ pub async fn container_render_positions(state: Rc<State>) {
     }
 }
 
+pub async fn container_tab_render_textures(state: Rc<State>) {
+    loop {
+        let container = state.pending_container_tab_render_textures.pop().await;
+        container.update_tab_textures_scheduled.set(false);
+        let (event, textures) = container.update_tab_textures_phase1();
+        event.triggered().await;
+        container.update_tab_textures_phase2(&textures);
+    }
+}
+
+impl ContainerNode {
+    fn update_tab_textures_phase1(
+        self: &Rc<Self>,
+    ) -> (Rc<crate::utils::asyncevent::AsyncEvent>, Vec<Rc<RefCell<Option<TextTexture>>>>) {
+        let on_completed = Rc::new(OnDropEvent::default());
+        let (entries, bar_height, render_scale) = {
+            let tab_bar = self.tab_bar.borrow();
+            let Some(tb) = tab_bar.as_ref() else {
+                return (on_completed.event(), vec![]);
+            };
+            let entries: Vec<_> = tb.entries.iter().map(|e| {
+                (e.title.clone(), TabBar::entry_colors(&self.state, e), e.title_texture.clone())
+            }).collect();
+            (entries, tb.height, tb.render_scale)
+        };
+        let Some(ctx) = self.state.render_ctx.get() else {
+            log::warn!("tab text phase1: no render context");
+            return (on_completed.event(), vec![]);
+        };
+        let font = self.state.theme.title_font();
+        let scale = if render_scale != Scale::from_int(1) {
+            Some(render_scale.to_f64())
+        } else {
+            None
+        };
+        let mut texture_height = bar_height;
+        if let Some(s) = scale {
+            texture_height = (bar_height as f64 * s).round() as _;
+        }
+        let mut scheduled = 0;
+        let mut texture_refs = Vec::new();
+        for (title, (_, _, text_color), title_texture) in &entries {
+            let mut tex_ref = title_texture.borrow_mut();
+            let tex = tex_ref.get_or_insert_with(|| TextTexture::new(&self.state, &ctx));
+            tex.schedule_render_fitting(
+                on_completed.clone(),
+                Some(texture_height),
+                &font,
+                title,
+                *text_color,
+                false,
+                scale,
+            );
+            texture_refs.push(title_texture.clone());
+            scheduled += 1;
+        }
+        (on_completed.event(), texture_refs)
+    }
+
+    fn update_tab_textures_phase2(&self, textures: &[Rc<RefCell<Option<TextTexture>>>]) {
+        for title_texture in textures {
+            let tex_ref = title_texture.borrow();
+            if let Some(tex) = tex_ref.as_ref() {
+                if let Err(e) = tex.flip() {
+                    log::warn!("Could not render tab text: {}", ErrorFmt(e));
+                }
+            }
+        }
+        self.damage();
+    }
+}
+
 impl Node for ContainerNode {
     fn node_id(&self) -> NodeId {
         self.id.into()
@@ -1329,8 +1765,9 @@ impl Node for ContainerNode {
         self.toplevel_data.node_layer()
     }
 
-    fn node_child_title_changed(self: Rc<Self>, _child: &dyn Node, _title: &str) {
-        // Titlebars removed; no title tracking needed
+    fn node_child_title_changed(self: Rc<Self>, child: &dyn Node, title: &str) {
+        self.rebuild_tab_bar_with_override(Some(child.node_id()), Some(title));
+        self.damage();
     }
 
     fn node_do_focus(self: Rc<Self>, seat: &Rc<WlSeatGlobal>, direction: Direction) {
@@ -1433,8 +1870,31 @@ impl Node for ContainerNode {
         self.button(id, seat, time_usec, state == ButtonState::Pressed, button);
     }
 
-    fn node_on_axis_event(self: Rc<Self>, _seat: &Rc<WlSeatGlobal>, _event: &PendingScroll) {
-        // Scroll-to-switch-tabs was a title bar feature; no-op without titles
+    fn node_on_axis_event(self: Rc<Self>, _seat: &Rc<WlSeatGlobal>, event: &PendingScroll) {
+        if self.mono_child.is_none() {
+            return;
+        }
+        // Use vertical scroll (index 1) to switch tabs.
+        let v = match event.v120[1].get() {
+            Some(v) if v != 0 => v,
+            _ => return,
+        };
+        let mono = match self.mono_child.get() {
+            Some(m) => m,
+            None => return,
+        };
+        let next = if v > 0 {
+            // Scroll down → next tab.
+            mono.next().or_else(|| self.children.first())
+        } else {
+            // Scroll up → previous tab.
+            mono.prev().or_else(|| self.children.last())
+        };
+        if let Some(next) = next {
+            if next.node.node_id() != mono.node.node_id() {
+                self.activate_child(&next);
+            }
+        }
     }
 
     fn node_on_leave(&self, seat: &WlSeatGlobal) {
@@ -1644,7 +2104,27 @@ impl ContainingNode for ContainerNode {
             }
         }
         self.sum_factors.set(sum);
+        // Ephemeral collapse: if this container is ephemeral and has exactly
+        // one child remaining, replace this container with that child in the parent.
+        if self.ephemeral.get() == Ephemeral::On
+            && num_children == 1
+            && !self.toplevel_data.is_fullscreen.get()
+        {
+            if let Some(parent) = self.toplevel_data.parent.get() {
+                if let Some(only_child) = self.children.first() {
+                    let child_node = only_child.node.clone();
+                    if parent.cnode_accepts_child(&*child_node) {
+                        parent.cnode_replace_child(self.deref(), child_node);
+                        self.toplevel_data.parent.take();
+                        self.child_nodes.borrow_mut().clear();
+                        self.tl_destroy();
+                        return;
+                    }
+                }
+            }
+        }
         // log::info!("cnode_remove_child2");
+        self.rebuild_tab_bar();
         self.schedule_layout();
         self.cancel_seat_ops();
         self.child_removed.trigger();
@@ -1664,6 +2144,8 @@ impl ContainingNode for ContainerNode {
             return;
         }
         self.mod_attention_requests(set);
+        drop(children);
+        self.rebuild_tab_bar();
         self.schedule_compute_render_positions();
     }
 
@@ -1882,6 +2364,13 @@ impl ToplevelNodeBase for ContainerNode {
         size_changed |= self.height.replace(rect.height()) != rect.height();
         if size_changed {
             self.update_content_size();
+            // Re-layout tab bar entries when container size changes in mono mode.
+            if self.mono_child.is_some() {
+                if let Some(bar) = self.tab_bar.borrow().as_ref() {
+                    let padding = self.state.theme.sizes.tab_bar_padding.get();
+                    bar.layout_entries(rect.width(), padding);
+                }
+            }
             // log::info!("tl_change_extents");
             self.perform_layout();
             self.cancel_seat_ops();

src/tree/tab_bar.rs

@@ -0,0 +1,113 @@
+use {
+    crate::{
+        scale::Scale,
+        state::State,
+        text::TextTexture,
+        theme::Color,
+        tree::NodeId,
+    },
+    std::{cell::{Cell, RefCell}, rc::Rc},
+};
+
+/// A single entry (tab) within a tab bar.
+pub struct TabBarEntry {
+    /// The node ID of the child this tab represents.
+    pub child_id: NodeId,
+    /// The display title of the tab.
+    pub title: String,
+    /// Pre-rendered text texture for the tab title.
+    pub title_texture: Rc<RefCell<Option<TextTexture>>>,
+    /// Whether this is the active (visible) tab.
+    pub active: bool,
+    /// Whether this tab's window has requested attention.
+    pub attention_requested: bool,
+    /// X offset of this tab within the tab bar (relative to tab bar start).
+    pub x: Cell<i32>,
+    /// Width of this tab in pixels.
+    pub width: Cell<i32>,
+}
+
+/// A tab bar rendered above a container in mono (tabbed) mode.
+pub struct TabBar {
+    /// The individual tab entries.
+    pub entries: Vec<TabBarEntry>,
+    /// Height of the tab bar in pixels (from theme).
+    pub height: i32,
+    /// The output scale at which text textures were rendered.
+    pub render_scale: Scale,
+}
+
+impl TabBar {
+    /// Create a new empty tab bar.
+    pub fn new(height: i32, render_scale: Scale) -> Self {
+        Self {
+            entries: Vec::new(),
+            height,
+            render_scale,
+        }
+    }
+
+    /// Recompute the positions and widths of all tab entries.
+    ///
+    /// `total_width` is the available width for the entire tab bar.
+    pub fn layout_entries(&self, total_width: i32, padding: i32) {
+        let n = self.entries.len() as i32;
+        if n == 0 {
+            return;
+        }
+        let total_padding = padding * (n + 1);
+        let available = (total_width - total_padding).max(0);
+        let per_tab = available / n;
+        let mut remainder = available - per_tab * n;
+        let mut x = padding;
+        for entry in &self.entries {
+            let w = if remainder > 0 {
+                remainder -= 1;
+                per_tab + 1
+            } else {
+                per_tab
+            };
+            entry.x.set(x);
+            entry.width.set(w);
+            x += w + padding;
+        }
+    }
+
+    /// Find the tab entry index at the given x coordinate (relative to tab bar).
+    ///
+    /// Returns `None` if the coordinate is in padding between tabs or out of bounds.
+    pub fn entry_at_x(&self, x: i32) -> Option<usize> {
+        for (i, entry) in self.entries.iter().enumerate() {
+            let ex = entry.x.get();
+            let ew = entry.width.get();
+            if x >= ex && x < ex + ew {
+                return Some(i);
+            }
+        }
+        None
+    }
+
+    /// Get the colors for a tab entry based on its state.
+    pub fn entry_colors(state: &State, entry: &TabBarEntry) -> (Color, Color, Color) {
+        let theme = &state.theme;
+        if entry.attention_requested {
+            (
+                theme.colors.tab_attention_background.get(),
+                theme.colors.tab_inactive_border.get(),
+                theme.colors.tab_active_text.get(),
+            )
+        } else if entry.active {
+            (
+                theme.colors.tab_active_background.get(),
+                theme.colors.tab_active_border.get(),
+                theme.colors.tab_active_text.get(),
+            )
+        } else {
+            (
+                theme.colors.tab_inactive_background.get(),
+                theme.colors.tab_inactive_border.get(),
+                theme.colors.tab_inactive_text.get(),
+            )
+        }
+    }
+}