Add configurable inactive dimming and viewport-paged scrolling

.gitignore

@@ -1,3 +1,3 @@
 /target/
 *.log
-
+ChatGPT Image*.png

README.md

@@ -29,7 +29,10 @@ cargo run -p ferese -- foot
 Set `RUST_LOG=ferese=debug` for detailed compositor logging.
 
 `Super+F` toggles decorated maximization inside the workspace (bar and outer
-gaps retained). `Super+Shift+F` toggles true fullscreen (no bar or window
+gaps remain visible). In scrolling mode this expands the column to full width,
+keeps it in the strip, and restores its previous width when toggled off. New
+windows open to its right and scroll into focus.
+`Super+Shift+F` toggles true fullscreen (no bar or window
 decorations). Leaving fullscreen restores the previous maximized/tiled state.
 
 Set `FERESE_TRACE_PERFORMANCE=1` to emit five-second per-output summaries under
@@ -108,8 +111,17 @@ opacity = 0.20
 [theme.material]
 style = "solid" # solid or translucent
 blur_radius = 12.0 # logical pixels; translucent only, 0 disables blur
+
+[appearance.inactive_dim]
+enabled = true # opt-in; disabled by default
+amount = 0.15 # dark tint over unfocused windows, 0–1; 0 disables
+duration_ms = 150 # 0 snaps immediately; reduced motion also snaps
 ```
 
+Inactive dimming follows window focus with a smooth, interruption-safe fade.
+It keeps window opacity intact, respects animated geometry and rounded corners,
+and leaves shell bars/popovers untouched. Overview temporarily removes dimming.
+
 Material roles use the configured surface color and role-specific shadows.
 Solid is the default. Translucent adds backdrop blur behind the same surface
 color, without grain, glossy lighting, saturation boosts, or inset highlights.
@@ -139,6 +151,13 @@ viewport only when focus must be revealed. Set
 `focus_strategy = "center_on_focus"` under `[scrolling]` to center focused
 columns instead.
 
+Use `focus_strategy = "paged"` to pack consecutive columns into viewport-sized
+pages. Half-width columns form pairs, thirds form triples, and full-width
+columns occupy their own page. Mixed widths and client minimum sizes use their
+actual allocated widths, including gaps. Focusing within a page keeps it still;
+crossing a page boundary scrolls to that page. Explicit centering remains in
+effect until focus changes or the output resizes.
+
 Scrolling controls use `Super+R` to cycle configured width presets, `Super+C`
 to center the focused column, `Super+[` to consume the focused window into an
 adjacent column, and `Super+]` to expel it. `Super+Ctrl+H/J/K/L` resizes in the

compositor/src/config.rs

@@ -114,6 +114,7 @@ pub struct ThemeSettings {
     pub shadow_color: RgbaColor,
     pub surface_base_color: RgbaColor,
     pub panel_opacity: f64,
+    pub inactive_dim: InactiveDimSettings,
     pub window_radius: f64,
     pub shadow_offset_y: f64,
     pub shadow_blur: f64,
@@ -135,6 +136,33 @@ pub enum MaterialStyle {
 #[derive(Debug, Default, Deserialize)]
 struct AppearanceConfig {
     corner_radius: Option<f64>,
+    #[serde(default)]
+    inactive_dim: InactiveDimConfig,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct InactiveDimSettings {
+    pub enabled: bool,
+    pub amount: f64,
+    pub duration_ms: f64,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(default)]
+struct InactiveDimConfig {
+    enabled: bool,
+    amount: f64,
+    duration_ms: f64,
+}
+
+impl Default for InactiveDimConfig {
+    fn default() -> Self {
+        Self {
+            enabled: false,
+            amount: 0.15,
+            duration_ms: 150.0,
+        }
+    }
 }
 
 #[derive(Debug, Default, Deserialize)]
@@ -518,6 +546,7 @@ struct ScrollingConfig {
 enum FocusStrategyValue {
     Minimal,
     CenterOnFocus,
+    Paged,
 }
 
 #[derive(Clone, Debug, Deserialize)]
@@ -680,6 +709,7 @@ impl Config {
         {
             FocusStrategyValue::Minimal => ViewportFocusStrategy::Minimal,
             FocusStrategyValue::CenterOnFocus => ViewportFocusStrategy::Center,
+            FocusStrategyValue::Paged => ViewportFocusStrategy::Paged,
         }
     }
 
@@ -862,6 +892,17 @@ impl Config {
                 self.theme.surface.bar.opacity.unwrap_or(0.78),
                 "surface.bar.opacity",
             )?,
+            inactive_dim: InactiveDimSettings {
+                enabled: self.appearance.inactive_dim.enabled,
+                amount: unit_theme_value(
+                    self.appearance.inactive_dim.amount,
+                    "appearance.inactive_dim.amount",
+                )?,
+                duration_ms: nonnegative_theme_value(
+                    self.appearance.inactive_dim.duration_ms,
+                    "appearance.inactive_dim.duration_ms",
+                )?,
+            },
             window_radius,
             shadow_offset_y,
             shadow_blur,
@@ -1576,6 +1617,11 @@ mod tests {
     fn parses_scrolling_focus_strategy() {
         let minimal = parse("");
         let centered = parse("[scrolling]\nfocus_strategy = \"center_on_focus\"");
+        let paged = parse("[scrolling]\nfocus_strategy = \"paged\"");
+        assert_eq!(
+            paged.scrolling_focus_strategy(),
+            ViewportFocusStrategy::Paged
+        );
 
         assert_eq!(
             minimal.scrolling_focus_strategy(),
@@ -1659,6 +1705,11 @@ mod tests {
                 shadow_color: RgbaColor([1.0 / 255.0, 2.0 / 255.0, 3.0 / 255.0, 128.0 / 255.0]),
                 surface_base_color: RgbaColor([17.0 / 255.0, 24.0 / 255.0, 33.0 / 255.0, 1.0,]),
                 panel_opacity: 0.78,
+                inactive_dim: InactiveDimSettings {
+                    enabled: false,
+                    amount: 0.15,
+                    duration_ms: 150.0
+                },
                 window_radius: 12.0,
                 shadow_offset_y: -2.0,
                 shadow_blur: 24.0,
@@ -1739,6 +1790,35 @@ mod tests {
         }
     }
 
+    #[test]
+    fn inactive_dimming_is_opt_in_and_configurable() {
+        let defaults = parse("").theme_settings().unwrap().inactive_dim;
+        assert!(!defaults.enabled);
+        assert_eq!(defaults.amount, 0.15);
+        assert_eq!(defaults.duration_ms, 150.0);
+        let settings =
+            parse("[appearance.inactive_dim]\nenabled = true\namount = 0.25\nduration_ms = 100")
+                .theme_settings()
+                .unwrap()
+                .inactive_dim;
+        assert!(settings.enabled);
+        assert_eq!(settings.amount, 0.25);
+        assert_eq!(settings.duration_ms, 100.0);
+        for (key, value) in [
+            ("amount", "-0.1"),
+            ("amount", "1.1"),
+            ("amount", "nan"),
+            ("duration_ms", "-1"),
+            ("duration_ms", "inf"),
+        ] {
+            assert!(
+                parse(&format!("[appearance.inactive_dim]\n{key} = {value}"))
+                    .theme_settings()
+                    .is_err()
+            );
+        }
+    }
+
     #[test]
     fn parses_input_and_touchpad_settings() {
         let config = parse(

compositor/src/dimming.rs

@@ -0,0 +1,129 @@
+use crate::config::InactiveDimSettings;
+use ferese_layout::WindowId;
+use std::time::Duration;
+
+pub(crate) fn target(
+    settings: InactiveDimSettings,
+    focused: Option<WindowId>,
+    window: WindowId,
+    overview: bool,
+) -> f64 {
+    if settings.enabled && !overview && focused.is_some() && focused != Some(window) {
+        settings.amount
+    } else {
+        0.0
+    }
+}
+
+/// A bounded, interruption-safe opacity transition; it never overshoots.
+#[derive(Debug)]
+pub(crate) struct DimAnimation {
+    pub current: f64,
+    start: f64,
+    target: f64,
+    elapsed: f64,
+}
+
+impl DimAnimation {
+    pub fn new(value: f64) -> Self {
+        Self {
+            current: value,
+            start: value,
+            target: value,
+            elapsed: 0.0,
+        }
+    }
+
+    pub fn advance(&mut self, target: f64, delta: Duration, duration_ms: f64) -> bool {
+        if self.target != target {
+            self.start = self.current;
+            self.target = target;
+            self.elapsed = 0.0;
+        }
+        if duration_ms == 0.0 {
+            self.current = target;
+            return false;
+        }
+        self.elapsed += delta.as_secs_f64() * 1000.0;
+        let progress = (self.elapsed / duration_ms).min(1.0);
+        if progress == 1.0 {
+            self.current = target;
+            return false;
+        }
+        let eased = progress * progress * (3.0 - 2.0 * progress);
+        self.current = self.start + (target - self.start) * eased;
+        self.current != target
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn only_unfocused_windows_dim_and_overview_disables_it() {
+        let settings = InactiveDimSettings {
+            enabled: true,
+            amount: 0.15,
+            duration_ms: 150.0,
+        };
+        let left = WindowId(1);
+        let right = WindowId(2);
+        assert_eq!(target(settings, Some(right), left, false), 0.15);
+        assert_eq!(target(settings, Some(right), right, false), 0.0);
+        assert_eq!(target(settings, Some(right), left, true), 0.0);
+        assert_eq!(target(settings, None, left, false), 0.0);
+        assert_eq!(
+            target(
+                InactiveDimSettings {
+                    enabled: false,
+                    ..settings
+                },
+                Some(right),
+                left,
+                false
+            ),
+            0.0
+        );
+        assert_eq!(
+            target(
+                InactiveDimSettings {
+                    amount: 0.0,
+                    ..settings
+                },
+                Some(right),
+                left,
+                false
+            ),
+            0.0
+        );
+    }
+
+    #[test]
+    fn focus_transition_is_smooth_bounded_and_settles() {
+        let mut dim = DimAnimation::new(0.0);
+        assert!(dim.advance(0.15, Duration::from_millis(75), 150.0));
+        assert!((dim.current - 0.075).abs() < 1e-9);
+        assert!(!dim.advance(0.15, Duration::from_millis(75), 150.0));
+        assert_eq!(dim.current, 0.15);
+        assert!(!dim.advance(0.15, Duration::from_secs(10), 150.0));
+    }
+
+    #[test]
+    fn reversing_focus_starts_from_current_opacity() {
+        let mut dim = DimAnimation::new(0.0);
+        dim.advance(0.15, Duration::from_millis(75), 150.0);
+        let before = dim.current;
+        assert!(dim.advance(0.0, Duration::ZERO, 150.0));
+        assert_eq!(dim.current, before);
+        assert!(!dim.advance(0.0, Duration::from_millis(150), 150.0));
+        assert_eq!(dim.current, 0.0);
+    }
+
+    #[test]
+    fn zero_duration_snaps_for_reduced_motion() {
+        let mut dim = DimAnimation::new(0.15);
+        assert!(!dim.advance(0.0, Duration::ZERO, 0.0));
+        assert_eq!(dim.current, 0.0);
+    }
+}

compositor/src/main.rs

@@ -3,6 +3,7 @@
 mod backends;
 mod config;
 mod cursor;
+mod dimming;
 mod effects;
 mod grabs;
 mod handlers;

compositor/src/state.rs

@@ -9,7 +9,7 @@ use std::{
 use ferese_animation::{AnimatedValue, ClientSize, PresentationMode, SpringConfig, WindowGeometry};
 use ferese_core::{
     LayoutMode, OutputGeometry, OutputId, OutputWorkspaceMap, WindowPlacement, WorkspaceId,
-    WorkspaceSet,
+    WorkspaceLayout, WorkspaceSet,
 };
 use ferese_layout::{
     Axis, ColumnWidth, Direction, GapConfig, LayoutResult, Rect, SizeConstraints,
@@ -119,8 +119,11 @@ pub struct Ferese {
     pub window_ids: HashMap<Window, WindowId>,
     pub window_geometry: HashMap<WindowId, WindowGeometry>,
     maximized_windows: HashSet<WindowId>,
+    maximized_column_widths: HashMap<WindowId, ColumnWidth>,
     window_stack: crate::stacking::WindowStack,
     pub(crate) window_borders: HashMap<WindowId, crate::winit::WindowBorderBuffers>,
+    pub(crate) window_dims: HashMap<WindowId, crate::winit::WindowBorderBuffers>,
+    pub(crate) window_dimming: HashMap<WindowId, crate::dimming::DimAnimation>,
     pub(crate) window_shadows: HashMap<WindowId, crate::winit::WindowShadowBuffers>,
     pub(crate) rounded_clip_programs: HashMap<ErasedContextId, crate::winit::RoundedClipPrograms>,
     pub(crate) overview_scrims: HashMap<OutputId, crate::winit::OverviewScrim>,
@@ -451,8 +454,11 @@ impl Ferese {
             window_ids: HashMap::new(),
             window_geometry: HashMap::new(),
             maximized_windows: HashSet::new(),
+            maximized_column_widths: HashMap::new(),
             window_stack: crate::stacking::WindowStack::default(),
             window_borders: HashMap::new(),
+            window_dims: HashMap::new(),
+            window_dimming: HashMap::new(),
             window_shadows: HashMap::new(),
             rounded_clip_programs: HashMap::new(),
             overview_scrims: HashMap::new(),
@@ -911,8 +917,11 @@ impl Ferese {
         self.space.unmap_elem(window);
         self.window_geometry.remove(&id);
         self.maximized_windows.remove(&id);
+        self.maximized_column_widths.remove(&id);
         self.window_stack.remove(id);
         self.window_borders.remove(&id);
+        self.window_dims.remove(&id);
+        self.window_dimming.remove(&id);
         self.window_shadows.remove(&id);
         self.closing_windows.remove(&id);
         self.window_rules_applied.remove(&id);
@@ -954,6 +963,7 @@ impl Ferese {
                 continue;
             };
             let workspace_fullscreen = workspace.fullscreen;
+            let is_scrolling_layout = matches!(workspace.layout, WorkspaceLayout::Scrolling(_));
             let workspace_focus = workspace.last_focused;
             let focused = self
                 .focused_window
@@ -1011,7 +1021,7 @@ impl Ferese {
                     self.maximized_windows.contains(id) && workspace_fullscreen != Some(*id);
                 let rect = if workspace_fullscreen == Some(*id) {
                     fullscreen_bounds
-                } else if is_maximized {
+                } else if is_maximized && !is_scrolling_layout {
                     maximized_rect(bounds, self.gap_config.outer)
                 } else {
                     match self.workspaces.placement(*id) {
@@ -1032,7 +1042,8 @@ impl Ferese {
                 );
 
                 visible.insert(*id);
-                let scrolling = if !is_fullscreen && !is_maximized && !is_floating {
+                let scrolling =
+                    if !is_fullscreen && !is_floating && (!is_maximized || is_scrolling_layout) {
                         viewport_target
                             .zip(viewport_current)
                             .map(|(target, current)| (workspace_id, rect.x + target, current))
@@ -1241,6 +1252,29 @@ impl Ferese {
             .collect::<Vec<_>>();
         let mut active_animation = false;
 
+        let dim_settings = self.theme_settings.inactive_dim;
+        let duration = if self.animations_enabled {
+            dim_settings.duration_ms
+        } else {
+            0.0
+        };
+        let mut dim_changed = false;
+        for (_, id) in &windows {
+            let target = crate::dimming::target(
+                dim_settings,
+                self.focused_window,
+                *id,
+                self.overview.is_presenting(),
+            );
+            let dim = self
+                .window_dimming
+                .entry(*id)
+                .or_insert_with(|| crate::dimming::DimAnimation::new(target));
+            let previous = dim.current;
+            active_animation |= dim.advance(target, delta, duration);
+            dim_changed |= previous != dim.current;
+        }
+
         let mut ready_to_close = Vec::new();
         for (id, animation) in &mut self.closing_windows {
             if animation.advance(delta) {
@@ -1346,7 +1380,7 @@ impl Ferese {
                 .advance(delta, self.spring_config, self.animations_enabled);
         self.sync_window_stacking();
 
-        if active_animation {
+        if active_animation || dim_changed {
             self.backdrop_generation = self.backdrop_generation.wrapping_add(1);
         }
         active_animation
@@ -1645,6 +1679,27 @@ impl Ferese {
         } else {
             self.maximized_windows.remove(&window);
         }
+        if self.workspaces.placement(window) == Some(WindowPlacement::Tiled) {
+            let workspace_id = self.workspaces.workspace_for_window(window).unwrap();
+            if let Some(workspace) = self.workspaces.workspace_mut(workspace_id) {
+                if let WorkspaceLayout::Scrolling(layout) = &mut workspace.layout {
+                    if enabled {
+                        if let Some(column) = layout
+                            .columns()
+                            .iter()
+                            .find(|column| column.windows.contains(&window))
+                        {
+                            self.maximized_column_widths
+                                .entry(window)
+                                .or_insert(column.width);
+                        }
+                        let _ = layout.set_column_width(window, ColumnWidth::Proportion(1.0));
+                    } else if let Some(width) = self.maximized_column_widths.remove(&window) {
+                        let _ = layout.set_column_width(window, width);
+                    }
+                }
+            }
+        }
         self.relayout();
     }
 

compositor/src/winit.rs

@@ -913,6 +913,22 @@ fn output_elements(
     for (window, id, visual, decoration_progress, close_alpha) in windows {
         let constrain = rounded_visual_rect(visual, output_geometry.loc);
 
+        let dim = state.window_dimming.get(&id).map_or(0.0, |dim| dim.current);
+        if let Some(overlay) = window_dim_element(
+            state,
+            renderer,
+            id,
+            constrain,
+            scale,
+            state.theme_settings.window_radius * decoration_progress,
+            dim as f32 * close_alpha,
+            output,
+        ) {
+            // Front-to-back: dim the application and its border, not its shadow
+            // or other windows/layer surfaces. The overlay is input-transparent.
+            elements.push(overlay.into());
+        }
+
         if let Some(programs) = rounded_clip_program.clone() {
             let window_radius = state.theme_settings.window_radius * decoration_progress;
             let shadow_offset_y = state.theme_settings.shadow_offset_y;
@@ -1163,6 +1179,72 @@ fn border_uniforms(parameters: &BorderParameters) -> Vec<Uniform<'static>> {
     ]
 }
 
+#[allow(clippy::too_many_arguments)]
+fn window_dim_element(
+    state: &mut Ferese,
+    renderer: &mut GlesRenderer,
+    id: ferese_layout::WindowId,
+    geometry: Rectangle<i32, Logical>,
+    scale: f64,
+    radius: f64,
+    amount: f32,
+    output: &Output,
+) -> Option<PixelShaderElement> {
+    if amount <= 0.0 {
+        state.window_dims.remove(&id);
+        return None;
+    }
+    let mode = output.current_mode()?;
+    let program = material_program(state, renderer)?;
+    let parameters = BorderParameters {
+        geometry,
+        clip_rect: framebuffer_clip_rect(
+            geometry.to_physical_precise_round(scale),
+            mode.size,
+            output.current_transform().invert(),
+        ),
+        radius: scaled_effect_value(radius, geometry, scale),
+        width: 0.0,
+        color: [0.0, 0.0, 0.0, amount.clamp(0.0, 1.0)],
+    };
+    let uniforms = |p: &BorderParameters| {
+        vec![
+            Uniform::new("visible_rect", p.clip_rect).into_owned(),
+            Uniform::new("material_radius", p.radius).into_owned(),
+            Uniform::new("tint", p.color).into_owned(),
+            Uniform::new("paint_mode", 0.0_f32).into_owned(),
+            Uniform::new("shadow_rect", p.clip_rect).into_owned(),
+            Uniform::new("shadow_values", [0.0_f32; 2]).into_owned(),
+        ]
+    };
+    let context = renderer.context_id().erased();
+    let buffers = state.window_dims.entry(id).or_default();
+    let cached = buffers
+        .contexts
+        .entry(context)
+        .or_insert_with(|| CachedBorder {
+            element: PixelShaderElement::new(
+                program.0,
+                geometry,
+                None,
+                1.0,
+                uniforms(&parameters),
+                RenderElementKind::Unspecified,
+            ),
+            parameters: parameters.clone(),
+        });
+    if cached.parameters != parameters {
+        if cached.parameters.geometry != geometry {
+            cached.element.resize(geometry, None);
+        }
+        // Updating uniforms advances the element's commit so unchanged client
+        // buffers still repaint while focus dimming animates.
+        cached.element.update_uniforms(uniforms(&parameters));
+        cached.parameters = parameters;
+    }
+    Some(cached.element.clone())
+}
+
 #[allow(clippy::too_many_arguments)]
 fn window_shadow_element(
     state: &mut Ferese,

crates/ferese-layout/src/scrolling.rs

@@ -24,6 +24,7 @@ pub enum ViewportFocusStrategy {
     #[default]
     Minimal,
     Center,
+    Paged,
 }
 
 impl Default for ColumnWidth {
@@ -79,6 +80,7 @@ pub struct ScrollingLayout {
     focus_strategy: ViewportFocusStrategy,
     reveal_pending: bool,
     width_cycle_pending: bool,
+    last_viewport_width: Option<f64>,
 }
 
 impl Default for ScrollingLayout {
@@ -92,6 +94,7 @@ impl Default for ScrollingLayout {
             focus_strategy: ViewportFocusStrategy::Minimal,
             reveal_pending: false,
             width_cycle_pending: false,
+            last_viewport_width: None,
         }
     }
 }
@@ -106,6 +109,7 @@ impl ScrollingLayout {
 
     pub fn set_focus_strategy(&mut self, strategy: ViewportFocusStrategy) {
         self.focus_strategy = strategy;
+        self.reveal_pending = true;
     }
 
     pub fn default_width(&self) -> ColumnWidth {
@@ -183,7 +187,9 @@ impl ScrollingLayout {
             column.active = column.active.min(column.windows.len() - 1);
             column.normalize_heights();
         }
-        self.reveal_pending |= removed_active_column && !self.columns.is_empty();
+        self.reveal_pending |= (removed_active_column
+            || self.focus_strategy == ViewportFocusStrategy::Paged)
+            && !self.columns.is_empty();
 
         debug_assert!(self.validate().is_ok());
         Ok(())
@@ -256,6 +262,7 @@ impl ScrollingLayout {
             .window_location(window)
             .ok_or(LayoutError::UnknownWindow(window))?;
         self.columns[column].width = normalized_width(width);
+        self.reveal_pending = true;
         Ok(())
     }
 
@@ -464,11 +471,15 @@ impl ScrollingLayout {
             column_positions.push((next_column_x, width));
             next_column_x += width + inner;
         }
+        let viewport_resized = self.last_viewport_width != Some(viewport_width);
+        self.last_viewport_width = Some(viewport_width);
         if self.width_cycle_pending {
             self.retarget_after_width_cycle(&column_positions, viewport_width);
             self.width_cycle_pending = false;
             self.reveal_pending = false;
-        } else if self.reveal_pending {
+        } else if self.reveal_pending
+            || (viewport_resized && self.focus_strategy == ViewportFocusStrategy::Paged)
+        {
             self.reveal_active_column(&column_positions, viewport_width);
             self.reveal_pending = false;
         }
@@ -504,6 +515,10 @@ impl ScrollingLayout {
     }
 
     fn reveal_active_column(&mut self, positions: &[(f64, f64)], viewport_width: f64) {
+        if let Some(start) = self.paged_viewport(positions, viewport_width) {
+            self.viewport_x = start;
+            return;
+        }
         let Some(active) = self.active_column else {
             return;
         };
@@ -536,7 +551,37 @@ impl ScrollingLayout {
         }
     }
 
+    fn paged_viewport(&self, positions: &[(f64, f64)], viewport_width: f64) -> Option<f64> {
+        if self.focus_strategy != ViewportFocusStrategy::Paged {
+            return None;
+        }
+        let active = self.active_column?;
+        // Pack actual allocated widths, including gaps and client constraints.
+        // Page boundaries are independent of focus direction. An oversized
+        // column occupies its own page rather than overlapping its neighbors.
+        let mut first = 0;
+        while first < positions.len() {
+            let (start, _) = positions[first];
+            let mut last = first;
+            while let Some(&(next_start, next_width)) = positions.get(last + 1) {
+                if next_start + next_width - start > viewport_width + 1e-6 {
+                    break;
+                }
+                last += 1;
+            }
+            if active <= last {
+                return Some(start);
+            }
+            first = last + 1;
+        }
+        None
+    }
+
     fn retarget_after_width_cycle(&mut self, positions: &[(f64, f64)], viewport_width: f64) {
+        if let Some(start) = self.paged_viewport(positions, viewport_width) {
+            self.viewport_x = start;
+            return;
+        }
         let Some(active) = self.active_column else {
             return;
         };
@@ -810,6 +855,188 @@ mod tests {
         );
     }
 
+    #[test]
+    fn full_width_column_stays_in_strip_when_new_half_window_opens() {
+        let (mut layout, bounds, gaps) = two_half_width_layout();
+        layout.set_focus_strategy(ViewportFocusStrategy::Paged);
+        layout
+            .set_column_width(window(2), ColumnWidth::Proportion(1.0))
+            .unwrap();
+        let zoomed = layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(2)))
+            .unwrap();
+        assert_eq!(zoomed.geometry[&window(2)].width, 980.0);
+        layout.insert(window(3), Some(window(2))).unwrap();
+        let opened = layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(3)))
+            .unwrap();
+        let previous = opened.geometry[&window(2)];
+        let new = opened.geometry[&window(3)];
+        assert_eq!(previous.width, 980.0);
+        assert_eq!(new, Rect::new(10.0, 10.0, 485.0, 780.0));
+        assert_eq!(previous.x + previous.width + gaps.inner, new.x);
+        assert_eq!(layout.active_window(), Some(window(3)));
+        layout
+            .set_column_width(window(2), ColumnWidth::Proportion(0.5))
+            .unwrap();
+        let restored = layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(2)))
+            .unwrap();
+        assert_eq!(restored.geometry[&window(2)].width, 485.0);
+    }
+
+    fn paged_layout(count: u64) -> (ScrollingLayout, Rect, GapConfig) {
+        let (mut layout, bounds, gaps) = two_half_width_layout();
+        layout.set_focus_strategy(ViewportFocusStrategy::Paged);
+        for id in 3..=count {
+            layout.insert(window(id), Some(window(id - 1))).unwrap();
+        }
+        (layout, bounds, gaps)
+    }
+
+    #[test]
+    fn paged_focus_snaps_six_half_columns_in_both_directions() {
+        let (mut layout, bounds, gaps) = paged_layout(6);
+        for focused in [1, 2, 3, 4, 5, 6, 5, 4, 3, 2, 1] {
+            let geometry = layout
+                .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(focused)))
+                .unwrap()
+                .geometry;
+            let first = (focused - 1) / 2 * 2 + 1;
+            assert_eq!(layout.viewport_x(), ((first - 1) / 2) as f64 * 990.0);
+            assert_eq!(geometry[&window(first)].x, 10.0);
+            assert_eq!(geometry[&window(first + 1)].x, 505.0);
+            assert_eq!(
+                geometry[&window(first + 1)].x + geometry[&window(first + 1)].width,
+                990.0
+            );
+        }
+    }
+
+    #[test]
+    fn paged_focus_realigns_after_output_resize() {
+        let (mut layout, bounds, gaps) = paged_layout(6);
+        layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(5)))
+            .unwrap();
+        let bounds = Rect::new(20.0, 48.0, 1400.0, 800.0);
+        let result = layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(5)))
+            .unwrap();
+        assert_eq!(layout.viewport_x(), 2780.0);
+        assert_eq!(result.geometry[&window(5)].x, 30.0);
+        assert_eq!(result.geometry[&window(6)].x, 725.0);
+    }
+
+    #[test]
+    fn paged_focus_preserves_explicit_center_until_focus_changes() {
+        let (mut layout, bounds, gaps) = paged_layout(4);
+        layout
+            .center_window(window(2), bounds, gaps, &HashMap::new())
+            .unwrap();
+        let result = layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(2)))
+            .unwrap();
+        let rect = result.geometry[&window(2)];
+        assert_eq!(rect.x + rect.width / 2.0, 500.0);
+        let result = layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(1)))
+            .unwrap();
+        assert_eq!(result.geometry[&window(1)].x, 10.0);
+    }
+
+    #[test]
+    fn full_width_column_occupies_its_own_page() {
+        let (mut layout, bounds, gaps) = paged_layout(4);
+        layout.columns[0].width = ColumnWidth::Full;
+        let result = layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(3)))
+            .unwrap();
+        assert_eq!(result.geometry[&window(2)].x, 10.0);
+        assert_eq!(result.geometry[&window(3)].x, 505.0);
+        let result = layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(4)))
+            .unwrap();
+        assert_eq!(result.geometry[&window(4)].x, 10.0);
+    }
+
+    #[test]
+    fn client_minimums_split_columns_across_pages() {
+        let (mut layout, bounds, gaps) = paged_layout(2);
+        let constraints = HashMap::from([(
+            window(1),
+            SizeConstraints {
+                min_width: 700.0,
+                ..Default::default()
+            },
+        )]);
+        let result = layout
+            .geometry_with_constraints(bounds, gaps, &constraints, Some(window(2)))
+            .unwrap();
+        assert!(layout.viewport_x() > 0.0);
+        let rect = result.geometry[&window(2)];
+        assert!(rect.x >= 10.0 && rect.x + rect.width <= 990.0);
+    }
+
+    #[test]
+    fn paged_focus_groups_thirds_in_both_directions_at_fractional_sizes() {
+        let (mut layout, _, gaps) = paged_layout(6);
+        for column in &mut layout.columns {
+            column.width = ColumnWidth::Proportion(1.0 / 3.0);
+        }
+        let bounds = Rect::new(13.25, 48.5, 1000.5, 800.25);
+        for focused in [1, 2, 3, 4, 5, 6, 5, 4, 3, 2, 1] {
+            let result = layout
+                .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(focused)))
+                .unwrap();
+            let first = (focused - 1) / 3 * 3 + 1;
+            assert!((result.geometry[&window(first)].x - 23.25).abs() < 1e-6);
+            let last = result.geometry[&window(first + 2)];
+            assert!((last.x + last.width - 1003.75).abs() < 1e-6);
+        }
+    }
+
+    #[test]
+    fn paged_focus_packs_mixed_widths_by_actual_fit() {
+        let (mut layout, bounds, gaps) = paged_layout(5);
+        let widths = [0.6, 0.4, 0.25, 0.5, 0.25];
+        for (column, width) in layout.columns.iter_mut().zip(widths) {
+            column.width = ColumnWidth::Proportion(width);
+        }
+        for (focused, first) in [(1, 1), (2, 1), (3, 3), (4, 3), (5, 3), (2, 1)] {
+            let result = layout
+                .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(focused)))
+                .unwrap();
+            assert_eq!(result.geometry[&window(first)].x, 10.0);
+            let rect = result.geometry[&window(focused)];
+            assert!(rect.x >= 10.0 && rect.x + rect.width <= 990.0 + 1e-6);
+        }
+    }
+
+    #[test]
+    fn oversized_page_does_not_absorb_neighbor_and_removal_repacks() {
+        let (mut layout, bounds, gaps) = paged_layout(4);
+        let constraints = HashMap::from([(
+            window(1),
+            SizeConstraints {
+                min_width: 1200.0,
+                ..Default::default()
+            },
+        )]);
+        let result = layout
+            .geometry_with_constraints(bounds, gaps, &constraints, Some(window(2)))
+            .unwrap();
+        assert_eq!(result.geometry[&window(2)].x, 10.0);
+        assert_eq!(result.geometry[&window(3)].x, 505.0);
+        layout.remove(window(1)).unwrap();
+        let result = layout
+            .geometry_with_constraints(bounds, gaps, &HashMap::new(), Some(window(2)))
+            .unwrap();
+        assert_eq!(layout.viewport_x(), 0.0);
+        assert_eq!(result.geometry[&window(2)].x, 10.0);
+        assert_eq!(result.geometry[&window(3)].x, 505.0);
+    }
+
     #[test]
     fn manual_resize_does_not_retarget_the_viewport() {
         let mut layout = ScrollingLayout::default();