Add mouse window controls and finer display scaling (#63)

Add configurable mouse and wheel bindings, window move and resize, tab drops, cross-output dragging, and device settings. Adjust display scaling in 0.05 increments.

Preserve opposite-edge positioning during scrolling resizes and show rows for edge drops into tabbed columns.

crates/ferese-layout/src/layout_tree.rs

@@ -279,6 +279,134 @@ impl LayoutTree {
         Ok(window_node)
     }
 
+    /// Reinsert a window beside a target, or into its tab group.
+    pub fn place_window(
+        &mut self,
+        window: WindowId,
+        target: WindowId,
+        placement: crate::DropPlacement,
+    ) -> Result<(), LayoutError> {
+        use crate::DropPlacement::*;
+        if !self.contains(window) {
+            return Err(LayoutError::UnknownWindow(window));
+        }
+        if !self.contains(target) {
+            return Err(LayoutError::UnknownWindow(target));
+        }
+        if window == target {
+            return Ok(());
+        }
+        if placement == Tab {
+            return self.stack_window(window, target);
+        }
+        let mut next = self.clone();
+        next.remove(window)?;
+        let axis = if matches!(placement, Left | Right) {
+            Axis::Horizontal
+        } else {
+            Axis::Vertical
+        };
+        let leaf = next.insert(window, Some(target), axis, 0.5)?;
+        if matches!(placement, Left | Above) {
+            let parent = next.parents[&leaf];
+            if let Some(Node::Split { first, second, .. }) = next.nodes.get_mut(&parent) {
+                std::mem::swap(first, second);
+            }
+        }
+        next.validate()?;
+        *self = next;
+        Ok(())
+    }
+
+    /// Move a selected split edge by a signed logical-pixel distance.
+    pub fn resize_edge(
+        &mut self,
+        window: WindowId,
+        edge: Direction,
+        delta: f64,
+        bounds: Rect,
+    ) -> Result<bool, LayoutError> {
+        let mut child = *self
+            .windows
+            .get(&window)
+            .ok_or(LayoutError::UnknownWindow(window))?;
+        if !delta.is_finite() {
+            return Ok(false);
+        }
+        while let Some(parent) = self.parents.get(&child).copied() {
+            let matches = match self.nodes.get(&parent) {
+                Some(Node::Split {
+                    axis: Axis::Horizontal,
+                    first,
+                    second,
+                    ..
+                }) => {
+                    (edge == Direction::Right && *first == child)
+                        || (edge == Direction::Left && *second == child)
+                }
+                Some(Node::Split {
+                    axis: Axis::Vertical,
+                    first,
+                    second,
+                    ..
+                }) => {
+                    (edge == Direction::Down && *first == child)
+                        || (edge == Direction::Up && *second == child)
+                }
+                _ => false,
+            };
+            if matches {
+                let mut path = Vec::new();
+                let mut node = parent;
+                while let Some(ancestor) = self.parents.get(&node).copied() {
+                    path.push((ancestor, node));
+                    node = ancestor;
+                }
+                let mut area = bounds;
+                for (ancestor, descendant) in path.into_iter().rev() {
+                    if let Some(Node::Split {
+                        axis, ratio, first, ..
+                    }) = self.nodes.get(&ancestor)
+                    {
+                        match axis {
+                            Axis::Horizontal => {
+                                let part = area.width * ratio;
+                                if *first == descendant {
+                                    area.width = part;
+                                } else {
+                                    area.x += part;
+                                    area.width -= part;
+                                }
+                            }
+                            Axis::Vertical => {
+                                let part = area.height * ratio;
+                                if *first == descendant {
+                                    area.height = part;
+                                } else {
+                                    area.y += part;
+                                    area.height -= part;
+                                }
+                            }
+                        }
+                    }
+                }
+                if let Some(Node::Split { ratio, .. }) = self.nodes.get_mut(&parent) {
+                    let extent = if matches!(edge, Direction::Left | Direction::Right) {
+                        area.width
+                    } else {
+                        area.height
+                    };
+                    let next = normalized_ratio(*ratio + delta / extent.max(1.0));
+                    let changed = next != *ratio;
+                    *ratio = next;
+                    return Ok(changed);
+                }
+            }
+            child = parent;
+        }
+        Ok(false)
+    }
+
     pub fn remove(&mut self, window: WindowId) -> Result<(), LayoutError> {
         let leaf = self
             .windows

crates/ferese-layout/src/lib.rs

@@ -6,3 +6,356 @@ pub use layout_tree::*;
 pub use scrolling::{
     Column, ColumnDisplay, ColumnWidth, ScrollingLayout, ViewportFocusStrategy, ViewportTarget,
 };
+
+/// The destination of an interactive tiled-window drop.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum DropPlacement {
+    Left,
+    Right,
+    Above,
+    Below,
+    Tab,
+}
+
+#[cfg(test)]
+mod pointer_tests {
+    use super::*;
+
+    #[test]
+    fn pointer_tree_drop_preserves_windows_and_is_atomic_for_unknown_targets() {
+        for placement in [
+            DropPlacement::Left,
+            DropPlacement::Right,
+            DropPlacement::Above,
+            DropPlacement::Below,
+            DropPlacement::Tab,
+        ] {
+            let mut tree = LayoutTree::default();
+            for id in 1..=4 {
+                tree.insert(WindowId(id), None, Axis::Horizontal, 0.5)
+                    .unwrap();
+            }
+            tree.place_window(WindowId(1), WindowId(3), placement)
+                .unwrap();
+            tree.validate().unwrap();
+            assert_eq!(tree.window_ids().count(), 4);
+            let before = tree.clone();
+            assert!(
+                tree.place_window(WindowId(1), WindowId(99), placement)
+                    .is_err()
+            );
+            assert_eq!(tree, before);
+            tree.place_window(WindowId(1), WindowId(1), placement)
+                .unwrap();
+            assert_eq!(tree, before);
+        }
+    }
+
+    #[test]
+    fn pointer_scrolling_drop_preserves_window_and_row_invariants() {
+        for placement in [
+            DropPlacement::Left,
+            DropPlacement::Right,
+            DropPlacement::Above,
+            DropPlacement::Below,
+            DropPlacement::Tab,
+        ] {
+            let mut layout = ScrollingLayout::default();
+            for id in 1..=4 {
+                layout.insert(WindowId(id), None).unwrap();
+            }
+            layout
+                .place_window(WindowId(1), WindowId(3), placement)
+                .unwrap();
+            layout.validate().unwrap();
+            assert_eq!(layout.window_ids().count(), 4);
+            let column = layout
+                .columns()
+                .iter()
+                .find(|column| column.windows.contains(&WindowId(1)))
+                .unwrap();
+            if placement == DropPlacement::Tab {
+                assert_eq!(column.display, ColumnDisplay::Tabbed);
+                assert_eq!(column.windows.len(), 2);
+            }
+            let before = layout.clone();
+            assert!(
+                layout
+                    .place_window(WindowId(1), WindowId(99), placement)
+                    .is_err()
+            );
+            assert_eq!(layout, before);
+        }
+    }
+
+    #[test]
+    fn pointer_tree_resize_moves_the_selected_boundary_in_both_directions() {
+        let mut tree = LayoutTree::default();
+        tree.insert(WindowId(1), None, Axis::Horizontal, 0.5)
+            .unwrap();
+        tree.insert(WindowId(2), Some(WindowId(1)), Axis::Horizontal, 0.5)
+            .unwrap();
+        let bounds = Rect::new(-1000.0, -500.0, 1000.0, 600.0);
+        let before = tree.geometry(bounds).unwrap();
+        assert!(
+            tree.resize_edge(WindowId(1), Direction::Right, 100.0, bounds)
+                .unwrap()
+        );
+        let after = tree.geometry(bounds).unwrap();
+        assert_eq!(
+            after[&WindowId(1)].width,
+            before[&WindowId(1)].width + 100.0
+        );
+        assert_eq!(
+            after[&WindowId(2)].width,
+            before[&WindowId(2)].width - 100.0
+        );
+        assert!(
+            tree.resize_edge(WindowId(2), Direction::Left, -100.0, bounds)
+                .unwrap()
+        );
+        assert_eq!(tree.geometry(bounds).unwrap(), before);
+        assert!(
+            !tree
+                .resize_edge(WindowId(1), Direction::Left, 100.0, bounds)
+                .unwrap()
+        );
+        assert!(
+            !tree
+                .resize_edge(WindowId(1), Direction::Right, f64::NAN, bounds)
+                .unwrap()
+        );
+    }
+}
+
+#[cfg(test)]
+mod pointer_sequence_tests {
+    use super::*;
+
+    #[test]
+    fn repeated_pointer_drops_and_resizes_keep_tabbed_layouts_valid() {
+        let mut tree = LayoutTree::default();
+        let mut scrolling = ScrollingLayout::default();
+        for id in 1..=8 {
+            tree.insert(WindowId(id), None, Axis::Horizontal, 0.5)
+                .unwrap();
+            scrolling.insert(WindowId(id), None).unwrap();
+        }
+        let bounds = Rect::new(-1200.0, -300.0, 1200.0, 800.0);
+        let mut seed = 42_u64;
+        for _ in 0..1000 {
+            seed = seed.wrapping_mul(6364136223846793005).wrapping_add(1);
+            let source = WindowId(1 + (seed >> 32) % 8);
+            let target = WindowId(1 + (seed >> 40) % 8);
+            let placement = [
+                DropPlacement::Left,
+                DropPlacement::Right,
+                DropPlacement::Above,
+                DropPlacement::Below,
+                DropPlacement::Tab,
+            ][(seed >> 48) as usize % 5];
+            tree.place_window(source, target, placement).unwrap();
+            scrolling.place_window(source, target, placement).unwrap();
+            let edge = [
+                Direction::Left,
+                Direction::Right,
+                Direction::Up,
+                Direction::Down,
+            ][(seed >> 52) as usize % 4];
+            let delta = (seed >> 16) as i16 as f64;
+            tree.resize_edge(source, edge, delta, bounds).unwrap();
+            scrolling.resize_edge(source, edge, delta, bounds).unwrap();
+            tree.validate().unwrap();
+            scrolling.validate().unwrap();
+            assert_eq!(tree.window_ids().count(), 8);
+            assert_eq!(scrolling.window_ids().count(), 8);
+            for id in 1..=8 {
+                assert!(tree.contains(WindowId(id)));
+                assert!(scrolling.contains(WindowId(id)));
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod pointer_regression_tests {
+    use super::*;
+    use std::collections::HashMap;
+
+    #[test]
+    fn edge_drop_on_tabbed_column_shows_rows_and_center_drop_keeps_tabs() {
+        for placement in [
+            DropPlacement::Above,
+            DropPlacement::Below,
+            DropPlacement::Tab,
+        ] {
+            let mut layout = ScrollingLayout::default();
+            for id in 1..=3 {
+                layout.insert(WindowId(id), None).unwrap();
+            }
+            layout
+                .place_window(WindowId(1), WindowId(2), DropPlacement::Tab)
+                .unwrap();
+            layout
+                .place_window(WindowId(3), WindowId(2), placement)
+                .unwrap();
+            let result = layout
+                .resolve_geometry_with_constraints(
+                    Rect::new(0.0, 0.0, 1200.0, 800.0),
+                    GapConfig::default(),
+                    &HashMap::new(),
+                    Some(WindowId(3)),
+                )
+                .unwrap();
+            layout.validate().unwrap();
+            assert_eq!(layout.window_ids().count(), 3);
+            if placement == DropPlacement::Tab {
+                assert_eq!(result.geometry.len(), 1);
+                assert!(result.geometry.contains_key(&WindowId(3)));
+                assert_eq!(layout.tab_group(WindowId(3)).unwrap().windows.len(), 3);
+            } else {
+                assert_eq!(result.geometry.len(), 3);
+                let dropped = result.geometry[&WindowId(3)];
+                let target = result.geometry[&WindowId(2)];
+                assert_eq!(dropped.y < target.y, placement == DropPlacement::Above);
+                assert!(layout.tab_group(WindowId(3)).is_none());
+            }
+        }
+    }
+
+    #[test]
+    fn left_resize_should_move_left_edge_and_preserve_right_edge() {
+        let mut layout = ScrollingLayout::default();
+        layout.insert(WindowId(1), None).unwrap();
+        let bounds = Rect::new(0.0, 0.0, 1200.0, 800.0);
+        let before = layout
+            .resolve_geometry_with_constraints(
+                bounds,
+                GapConfig::default(),
+                &HashMap::new(),
+                Some(WindowId(1)),
+            )
+            .unwrap()
+            .geometry[&WindowId(1)];
+        layout
+            .resize_edge(WindowId(1), Direction::Left, 100.0, bounds)
+            .unwrap();
+        let after = layout
+            .resolve_geometry_with_constraints(
+                bounds,
+                GapConfig::default(),
+                &HashMap::new(),
+                Some(WindowId(1)),
+            )
+            .unwrap()
+            .geometry[&WindowId(1)];
+        assert_eq!(
+            after.x + after.width,
+            before.x + before.width,
+            "left-edge drag changed the right edge: {before:?} -> {after:?}"
+        );
+    }
+
+    #[test]
+    fn horizontal_resize_anchors_survive_limits_focus_policies_and_held_buffers() {
+        let bounds = Rect::new(-1200.0, -300.0, 1200.0, 800.0);
+        for strategy in [
+            ViewportFocusStrategy::Minimal,
+            ViewportFocusStrategy::Center,
+            ViewportFocusStrategy::Paged,
+        ] {
+            for tabbed in [false, true] {
+                for constraint in [
+                    SizeConstraints::default(),
+                    SizeConstraints {
+                        min_width: 700.0,
+                        ..Default::default()
+                    },
+                    SizeConstraints {
+                        max_width: Some(250.0),
+                        ..Default::default()
+                    },
+                ] {
+                    let mut base = ScrollingLayout::default();
+                    base.set_focus_strategy(strategy);
+                    for id in 1..=3 {
+                        base.insert(WindowId(id), None).unwrap();
+                    }
+                    if tabbed {
+                        base.place_window(WindowId(3), WindowId(2), DropPlacement::Tab)
+                            .unwrap();
+                    }
+                    let window = WindowId(2);
+                    let constraints =
+                        HashMap::from([(if tabbed { WindowId(3) } else { window }, constraint)]);
+                    let before = base
+                        .resolve_geometry_with_constraints(
+                            bounds,
+                            GapConfig::default(),
+                            &constraints,
+                            Some(window),
+                        )
+                        .unwrap()
+                        .geometry[&window];
+                    let initial_viewport = base.viewport_x();
+                    let initial_width = base.allocated_column_width(window).unwrap();
+                    for direction in [Direction::Left, Direction::Right] {
+                        for delta in [-1000.0, -100.0, 100.0, 1000.0] {
+                            let mut layout = base.clone();
+                            layout
+                                .resize_edge(window, direction, delta, bounds)
+                                .unwrap();
+                            let after = layout
+                                .resolve_geometry_with_constraints(
+                                    bounds,
+                                    GapConfig::default(),
+                                    &constraints,
+                                    Some(window),
+                                )
+                                .unwrap()
+                                .geometry[&window];
+                            let edge = |rect: Rect| {
+                                if direction == Direction::Left {
+                                    rect.x + rect.width
+                                } else {
+                                    rect.x
+                                }
+                            };
+                            assert!(
+                                (edge(after) - edge(before)).abs() < 0.001,
+                                "{direction:?} {delta} {strategy:?} {constraint:?}: {before:?} -> {after:?}"
+                            );
+                            let target = layout.viewport_target().unwrap();
+                            let held = target.with_held_widths(
+                                &[(
+                                    window,
+                                    initial_width,
+                                    layout.allocated_column_width(window).unwrap(),
+                                )],
+                                None,
+                            );
+                            assert!(
+                                (held - initial_viewport).abs() < 0.001,
+                                "pending buffers must retain the old viewport"
+                            );
+                            let settled = layout.clone();
+                            layout
+                                .resolve_geometry_with_constraints(
+                                    bounds,
+                                    GapConfig::default(),
+                                    &constraints,
+                                    Some(window),
+                                )
+                                .unwrap();
+                            assert_eq!(
+                                layout, settled,
+                                "an idle relayout must not reapply the resize"
+                            );
+                            layout.validate().unwrap();
+                        }
+                    }
+                }
+            }
+        }
+    }
+}

crates/ferese-layout/src/scrolling.rs

@@ -121,6 +121,12 @@ enum ViewportRequest {
     WidthCycle(usize),
     Slide(usize, usize),
     Center(usize, Option<f64>),
+    Resize {
+        column: usize,
+        anchor: f64,
+        anchor_right: bool,
+        maximum: Option<f64>,
+    },
 }
 
 impl ViewportTarget {
@@ -162,6 +168,18 @@ impl ViewportTarget {
                 });
                 layout.viewport_x = positions[active].0 + width / 2.0 - self.viewport_width / 2.0
             }
+            ViewportRequest::Resize {
+                column,
+                anchor,
+                anchor_right,
+                maximum,
+            } => {
+                let width = maximum.map_or(positions[column].1, |maximum| {
+                    positions[column].1.min(maximum)
+                });
+                layout.viewport_x =
+                    positions[column].0 + if anchor_right { width } else { 0.0 } - anchor;
+            }
         }
         layout.viewport_x
     }
@@ -204,6 +222,14 @@ enum PendingViewportRequest {
     // Width cycling takes precedence. Keep the focus request only in case a
     // subsequent no-op cycle cancels the width request before layout resolves.
     WidthCycle(Option<PendingFocusRequest>),
+    // Resolve the opposite edge from the previous strip position and allocation
+    // after applying client limits. Negative offsets keep the first column anchored.
+    Resize {
+        window: WindowId,
+        origin: f64,
+        width: f64,
+        anchor_right: bool,
+    },
 }
 
 #[derive(Clone, Debug, PartialEq)]
@@ -242,11 +268,18 @@ impl ScrollingLayout {
         match self.pending_viewport {
             Some(PendingViewportRequest::Focus(request)) => Some(request),
             Some(PendingViewportRequest::WidthCycle(request)) => request,
-            None => None,
+            None | Some(PendingViewportRequest::Resize { .. }) => None,
         }
     }
 
     fn request_focus(&mut self, request: Option<PendingFocusRequest>) {
+        // Direct manipulation keeps its edge anchor through the next solve.
+        if matches!(
+            self.pending_viewport,
+            Some(PendingViewportRequest::Resize { .. })
+        ) {
+            return;
+        }
         self.pending_viewport = if matches!(
             self.pending_viewport,
             Some(PendingViewportRequest::WidthCycle(_))
@@ -371,6 +404,37 @@ impl ScrollingLayout {
         self.viewport_x
     }
 
+    /// Pan without changing focus, keeping the viewport inside the column strip.
+    pub fn scroll_viewport(&mut self, delta: f64) -> bool {
+        let Some(sizing) = self.last_column_sizing else {
+            return false;
+        };
+        if !delta.is_finite() || delta == 0.0 {
+            return false;
+        }
+        let width = self
+            .columns
+            .iter()
+            .map(|column| {
+                column
+                    .windows
+                    .first()
+                    .and_then(|id| self.allocated_widths.get(id))
+                    .copied()
+                    .unwrap_or_else(|| sizing.resolve(column.width))
+            })
+            .sum::<f64>()
+            + sizing.inner_gap * self.columns.len().saturating_sub(1) as f64;
+        let next = (self.viewport_x + delta).clamp(0.0, (width - sizing.viewport_width).max(0.0));
+        if next == self.viewport_x {
+            return false;
+        }
+        self.viewport_x = next;
+        self.pending_viewport = None;
+        self.viewport_basis = None;
+        true
+    }
+
     #[must_use]
     pub fn allocated_column_width(&self, window: WindowId) -> Option<f64> {
         self.allocated_widths.get(&window).copied()
@@ -450,6 +514,133 @@ impl ScrollingLayout {
         Ok(())
     }
 
+    pub fn place_window(
+        &mut self,
+        window: WindowId,
+        target: WindowId,
+        placement: crate::DropPlacement,
+    ) -> Result<(), LayoutError> {
+        use crate::DropPlacement::*;
+        let (source, _) = self
+            .window_location(window)
+            .ok_or(LayoutError::UnknownWindow(window))?;
+        if !self.contains(target) {
+            return Err(LayoutError::UnknownWindow(target));
+        }
+        if window == target {
+            return Ok(());
+        }
+        let width = self.columns[source].width;
+        self.remove(window)?;
+        let (column, row) = self
+            .window_location(target)
+            .expect("target survives removing another window");
+        match placement {
+            Left | Right => {
+                let index = column + usize::from(placement == Right);
+                let mut entry = Column::new(window, width);
+                entry.display = self.default_display;
+                self.columns.insert(index, entry);
+                self.active_column = Some(index);
+            }
+            Above | Below | Tab => {
+                let entry = &mut self.columns[column];
+                let index = row + usize::from(placement != Above);
+                entry.windows.insert(index, window);
+                // Split the destination row's weight rather than collapsing it.
+                let weight = entry.heights[row] / 2.0;
+                entry.heights[row] = weight;
+                entry.heights.insert(index, weight);
+                entry.normalize_heights();
+                entry.display = if placement == Tab {
+                    ColumnDisplay::Tabbed
+                } else {
+                    ColumnDisplay::Stacked
+                };
+                entry.active = index;
+                self.active_column = Some(column);
+            }
+        }
+        self.request_reveal(Some(window));
+        debug_assert!(self.validate().is_ok());
+        Ok(())
+    }
+
+    pub fn resize_edge(
+        &mut self,
+        window: WindowId,
+        edge: Direction,
+        delta: f64,
+        bounds: Rect,
+    ) -> Result<bool, LayoutError> {
+        let (column, row) = self
+            .window_location(window)
+            .ok_or(LayoutError::UnknownWindow(window))?;
+        if !delta.is_finite() {
+            return Ok(false);
+        }
+        if matches!(edge, Direction::Left | Direction::Right) {
+            let size = self.last_column_sizing.unwrap_or(ColumnSizing {
+                viewport_width: bounds.width,
+                inner_gap: 0.0,
+            });
+            let width = self
+                .allocated_column_width(window)
+                .unwrap_or_else(|| size.resolve(self.columns[column].width));
+            let origin = self.columns[..column]
+                .iter()
+                .map(|column| {
+                    self.allocated_column_width(column.windows[0])
+                        .unwrap_or_else(|| size.resolve(column.width))
+                        + size.inner_gap
+                })
+                .sum::<f64>()
+                - self.viewport_x;
+            let change = if edge == Direction::Left {
+                -delta
+            } else {
+                delta
+            };
+            let next = (width + change).clamp(
+                size.resolve(ColumnWidth::Proportion(MIN_COLUMN_WIDTH))
+                    .max(1.0),
+                size.resolve(ColumnWidth::Proportion(MAX_COLUMN_WIDTH))
+                    .max(1.0),
+            );
+            if next == width {
+                return Ok(false);
+            }
+            self.columns[column].width = ColumnWidth::Fixed(next);
+            self.pending_viewport = Some(PendingViewportRequest::Resize {
+                window,
+                origin,
+                width,
+                anchor_right: edge == Direction::Left,
+            });
+            return Ok(true);
+        }
+        let entry = &mut self.columns[column];
+        if entry.display == ColumnDisplay::Tabbed {
+            return Ok(false);
+        }
+        let neighbor = match edge {
+            Direction::Up => row.checked_sub(1),
+            Direction::Down => (row + 1 < entry.windows.len()).then_some(row + 1),
+            _ => None,
+        };
+        let Some(neighbor) = neighbor else {
+            return Ok(false);
+        };
+        let pair = entry.heights[row] + entry.heights[neighbor];
+        let change = (if edge == Direction::Up { -delta } else { delta }) / bounds.height.max(1.0);
+        let minimum = MIN_ROW_HEIGHT.min(pair / 2.0);
+        let height = (entry.heights[row] + change).clamp(minimum, pair - minimum);
+        let changed = height != entry.heights[row];
+        entry.heights[row] = height;
+        entry.heights[neighbor] = pair - height;
+        Ok(changed)
+    }
+
     pub fn remove(&mut self, window: WindowId) -> Result<(), LayoutError> {
         let (column_index, window_index) = self
             .window_location(window)
@@ -897,6 +1088,42 @@ impl ScrollingLayout {
             self.last_column_sizing.map(|sizing| sizing.viewport_width) != Some(viewport_width);
         self.last_column_sizing = Some(sizing);
         match self.pending_viewport.take() {
+            Some(PendingViewportRequest::Resize {
+                window,
+                origin,
+                width,
+                anchor_right,
+            }) => {
+                if let Some((column, _)) = self.window_location(window) {
+                    let constraint = if self.columns[column].display == ColumnDisplay::Tabbed {
+                        tab_constraints(&self.columns[column], constraints)
+                    } else {
+                        layout_tree::normalized_constraints(
+                            constraints.get(&window).copied().unwrap_or_default(),
+                        )
+                    };
+                    let maximum = constraint.max_width;
+                    let previous_width = maximum.map_or(width, |maximum| width.min(maximum));
+                    let anchor = origin + if anchor_right { previous_width } else { 0.0 };
+                    let next_width = maximum.map_or(column_positions[column].1, |maximum| {
+                        column_positions[column].1.min(maximum)
+                    });
+                    self.record_viewport_basis(
+                        &column_positions,
+                        inner,
+                        viewport_width,
+                        ViewportRequest::Resize {
+                            column,
+                            anchor,
+                            anchor_right,
+                            maximum,
+                        },
+                    );
+                    self.viewport_x = column_positions[column].0
+                        + if anchor_right { next_width } else { 0.0 }
+                        - anchor;
+                }
+            }
             Some(PendingViewportRequest::WidthCycle(_)) => {
                 if let Some(active) = self.active_column {
                     self.record_viewport_basis(
@@ -970,23 +1197,7 @@ impl ScrollingLayout {
                 );
                 // All tabs use one size, even when their client constraints differ.
                 // Keep the column allocation stable and honor compatible maximums.
-                let mut common = SizeConstraints::default();
-                for id in &column.windows {
-                    let c = layout_tree::normalized_constraints(
-                        constraints.get(id).copied().unwrap_or_default(),
-                    );
-                    common.min_width = common.min_width.max(c.min_width);
-                    common.min_height = common.min_height.max(c.min_height);
-                    common.max_width = match (common.max_width, c.max_width) {
-                        (Some(a), Some(b)) => Some(a.min(b)),
-                        (a, b) => a.or(b),
-                    };
-                    common.max_height = match (common.max_height, c.max_height) {
-                        (Some(a), Some(b)) => Some(a.min(b)),
-                        (a, b) => a.or(b),
-                    };
-                }
-                let common = layout_tree::normalized_constraints(common);
+                let common = tab_constraints(column, constraints);
                 layout_tree::record_minimum_warnings(window, rect, common, &mut result.warnings);
                 apply_maximums(window, &mut rect, common, &mut result.warnings);
                 if column.windows.len() > 1 {
@@ -1331,6 +1542,28 @@ fn finite_nonnegative(value: f64) -> f64 {
     }
 }
 
+fn tab_constraints(
+    column: &Column,
+    constraints: &HashMap<WindowId, SizeConstraints>,
+) -> SizeConstraints {
+    let mut common = SizeConstraints::default();
+    for id in &column.windows {
+        let c =
+            layout_tree::normalized_constraints(constraints.get(id).copied().unwrap_or_default());
+        common.min_width = common.min_width.max(c.min_width);
+        common.min_height = common.min_height.max(c.min_height);
+        common.max_width = match (common.max_width, c.max_width) {
+            (Some(a), Some(b)) => Some(a.min(b)),
+            (a, b) => a.or(b),
+        };
+        common.max_height = match (common.max_height, c.max_height) {
+            (Some(a), Some(b)) => Some(a.min(b)),
+            (a, b) => a.or(b),
+        };
+    }
+    layout_tree::normalized_constraints(common)
+}
+
 fn apply_maximums(
     window: WindowId,
     rect: &mut Rect,