monolith

public

Star0

Watch0

72 commits 1 branch 0 tags 0 releases1.5 MiB

use monolith_planner::Rect;
use slotmap::{SlotMap, new_key_type};
use std::collections::HashMap;
use std::hash::Hash;

new_key_type! { pub struct NodeId; }

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum Axis {
    Horizontal,
    Vertical,
}

impl Axis {
    pub fn other(self) -> Self {
        match self {
            Self::Horizontal => Self::Vertical,
            Self::Vertical => Self::Horizontal,
        }
    }
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum Dir {
    Left,
    Right,
    Up,
    Down,
}

impl Dir {
    pub fn axis(self) -> Axis {
        match self {
            Self::Left | Self::Right => Axis::Horizontal,
            Self::Up | Self::Down => Axis::Vertical,
        }
    }

    pub fn forward(self) -> bool {
        matches!(self, Self::Right | Self::Down)
    }
}

const MIN_SHARE: f64 = 0.05;

#[derive(Clone, Debug)]
struct Child {
    node: NodeId,
    weight: f64,
}

#[derive(Clone, Debug)]
enum Kind<W> {
    Leaf(W),
    Container {
        axis: Axis,
        children: Vec<Child>,
        expanded: Option<NodeId>,
    },
}

#[derive(Clone, Debug)]
struct Node<W> {
    parent: Option<NodeId>,
    kind: Kind<W>,
}

/// One output's tiling tree. Every tiled window of every tag lives here, the
/// caller's visibility filter decides which ones take space.
///
/// Children run on the axis opposite their parent. Containers hold at least
/// two children, hidden ones included, and a container left with one child
/// is replaced by it.
#[derive(Clone, Debug)]
pub struct Tree<W> {
    nodes: SlotMap<NodeId, Node<W>>,
    root: Option<NodeId>,
    leaves: HashMap<W, NodeId>,
    stack: Axis,
}

impl<W: Copy + Eq + Hash> Default for Tree<W> {
    fn default() -> Self {
        Self {
            nodes: SlotMap::with_key(),
            root: None,
            leaves: HashMap::new(),
            stack: Axis::Vertical,
        }
    }
}

impl<W: Copy + Eq + Hash> Tree<W> {
    /// The axis tag rows stack along.
    pub fn stack_axis(&self) -> Axis {
        self.stack
    }

    pub fn contains(&self, w: W) -> bool {
        self.leaves.contains_key(&w)
    }

    pub fn is_empty(&self) -> bool {
        self.root.is_none()
    }

    pub fn windows(&self) -> impl Iterator<Item = W> + '_ {
        self.leaves.keys().copied()
    }

    /// Inserts `w` as the next sibling of `anchor`, or as a new row if
    /// `anchor` is not in the tree.
    pub fn insert_after(&mut self, w: W, anchor: W) {
        let Some(&a) = self.leaves.get(&anchor) else {
            return self.insert_row(w);
        };
        let n = self.new_leaf(w);
        match self.position(a) {
            Some((p, i)) if Some(p) == self.root && self.axis(p) == Some(self.stack) => {
                let weight = self.unlink(p, i).weight;
                let c = self.new_container(self.stack.other());
                self.attach(c, 0, a, 1.0);
                self.attach(c, 1, n, 1.0);
                self.attach(p, i, c, weight);
            }
            Some((p, i)) => {
                let weight = self.mean_weight(p);
                self.attach(p, i + 1, n, weight);
            }
            None => {
                let c = self.new_container(self.stack.other());
                self.attach(c, 0, a, 1.0);
                self.attach(c, 1, n, 1.0);
                self.root = Some(c);
            }
        }
    }

    /// Appends `w` as a row of its own along the stacking axis.
    pub fn insert_row(&mut self, w: W) {
        let n = self.new_leaf(w);
        match self.root {
            None => self.root = Some(n),
            Some(r) if self.axis(r) == Some(self.stack) => {
                let weight = self.mean_weight(r);
                let end = self.children(r).len();
                self.attach(r, end, n, weight);
            }
            Some(r) => {
                let c = self.new_container(self.stack);
                self.attach(c, 0, r, 1.0);
                self.attach(c, 1, n, 1.0);
                self.root = Some(c);
            }
        }
    }

    pub fn remove(&mut self, w: W) -> bool {
        let Some(n) = self.leaves.remove(&w) else {
            return false;
        };
        self.detach(n);
        self.nodes.remove(n);
        true
    }

    pub fn retain(&mut self, mut keep: impl FnMut(W) -> bool) {
        let gone: Vec<W> = self.windows().filter(|&w| !keep(w)).collect();
        for w in gone {
            self.remove(w);
        }
    }

    /// Moves a window one step in `dir`. Leaves swap slots with the next
    /// visible sibling, enter a sibling container, or step out beside their
    /// container. Hidden windows never move.
    pub fn move_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
        let Some(&n) = self.leaves.get(&w) else {
            return false;
        };
        self.move_node(n, dir, &vis, true)
    }

    /// Moves the container holding `w` as a rigid block. A window sitting
    /// directly in the root is its own block.
    pub fn move_container(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
        let Some(&n) = self.leaves.get(&w) else {
            return false;
        };
        let block = self.nodes[n]
            .parent
            .filter(|&p| Some(p) != self.root)
            .unwrap_or(n);
        self.move_node(block, dir, &vis, false)
    }

    /// Moves a window to the end of the next visible lane in `dir`, stepping
    /// up a level when its container has none that way. A lone window there
    /// becomes a stack with it.
    pub fn merge_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
        let Some(&n) = self.leaves.get(&w) else {
            return false;
        };
        let mut cur = n;
        while let Some((p, i)) = self.position(cur) {
            if self.axis(p) == Some(dir.axis())
                && let Some(j) = self.next_shown(p, i, dir, &vis)
            {
                self.join_lane(n, p, j);
                return true;
            }
            cur = p;
        }
        false
    }

    /// Whether every container above `w` is expanded towards it.
    pub fn maximized(&self, w: W) -> bool {
        let Some(&leaf) = self.leaves.get(&w) else {
            return false;
        };
        let mut cur = leaf;
        let mut any = false;
        while let Some(p) = self.nodes[cur].parent {
            if self.expanded(p) != Some(cur) {
                return false;
            }
            any = true;
            cur = p;
        }
        any
    }

    /// Transposes the whole tree.
    pub fn flip(&mut self) {
        self.stack = self.stack.other();
        for node in self.nodes.values_mut() {
            if let Kind::Container { axis, .. } = &mut node.kind {
                *axis = axis.other();
            }
        }
    }

    /// Toggles expansion for `count` levels of `w`'s ancestry, starting
    /// `skip` levels up. Level 0 expands the window inside its container.
    pub fn toggle_expand(&mut self, w: W, skip: usize, count: usize) -> bool {
        let Some(&leaf) = self.leaves.get(&w) else {
            return false;
        };
        let mut path = Vec::new();
        let mut cur = leaf;
        while let Some(p) = self.nodes[cur].parent {
            path.push((p, cur));
            cur = p;
        }
        let path: Vec<_> = path.into_iter().skip(skip).take(count).collect();
        if path.is_empty() {
            return false;
        }
        let all = path.iter().all(|&(p, c)| self.expanded(p) == Some(c));
        for (p, c) in path {
            if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind {
                *expanded = (!all).then_some(c);
            }
        }
        true
    }

    /// Grows `w` by `delta`, a fraction of the visible length of the nearest
    /// container along `axis` where it has a visible sibling. Hidden siblings
    /// keep their weights, and with them their share.
    pub fn resize(&mut self, w: W, axis: Axis, delta: f64, vis: impl Fn(W) -> bool) -> bool {
        let Some(&leaf) = self.leaves.get(&w) else {
            return false;
        };
        let mut cur = leaf;
        while let Some((p, i)) = self.position(cur) {
            if self.axis(p) == Some(axis) {
                let shown: Vec<usize> = (0..self.children(p).len())
                    .filter(|&j| self.visible(self.children(p)[j].node, &vis))
                    .collect();
                if shown.len() >= 2 {
                    let children = self.children_mut(p);
                    let sum: f64 = shown.iter().map(|&j| children[j].weight).sum();
                    let old = children[i].weight;
                    let max = 1.0 - MIN_SHARE * (shown.len() - 1) as f64;
                    let new = (old / sum + delta).clamp(MIN_SHARE, max) * sum;
                    let scale = (sum - new) / (sum - old);
                    for j in shown {
                        children[j].weight = if j == i {
                            new
                        } else {
                            children[j].weight * scale
                        };
                    }
                    return true;
                }
            }
            cur = p;
        }
        false
    }

    /// Lays the tree out in `area`. Hidden windows come back as zero-size
    /// rects on the boundary where they would reappear.
    pub fn arrange(&self, area: Rect, gap: f64, vis: impl Fn(W) -> bool) -> Vec<(W, Rect)> {
        let mut out = Vec::with_capacity(self.leaves.len());
        if let Some(r) = self.root {
            let area = if self.visible(r, &vis) {
                area
            } else {
                Rect::new(area.x + area.w / 2.0, area.y, 0.0, area.h)
            };
            self.place(r, area, gap, &vis, &mut out);
        }
        out
    }

    fn place(
        &self,
        n: NodeId,
        r: Rect,
        gap: f64,
        vis: &impl Fn(W) -> bool,
        out: &mut Vec<(W, Rect)>,
    ) {
        let (axis, children, expanded) = match &self.nodes[n].kind {
            Kind::Leaf(w) => return out.push((*w, r)),
            Kind::Container {
                axis,
                children,
                expanded,
            } => (*axis, children, *expanded),
        };
        let shown: Vec<bool> = children.iter().map(|c| self.visible(c.node, vis)).collect();
        let (start, len) = span(r, axis);
        if let Some(e) = expanded.and_then(|e| children.iter().position(|c| c.node == e))
            && shown[e]
        {
            for (i, c) in children.iter().enumerate() {
                let sub = match i.cmp(&e) {
                    std::cmp::Ordering::Equal => r,
                    std::cmp::Ordering::Less => with_span(r, axis, start, 0.0),
                    std::cmp::Ordering::Greater => with_span(r, axis, start + len, 0.0),
                };
                self.place(c.node, sub, gap, vis, out);
            }
            return;
        }
        let count = shown.iter().filter(|s| **s).count();
        let total: f64 = children
            .iter()
            .zip(&shown)
            .filter(|(_, s)| **s)
            .map(|(c, _)| c.weight)
            .sum();
        let gaps = count.saturating_sub(1) as f64;
        let gap = if gaps > 0.0 { gap.min(len / gaps) } else { gap };
        let avail = len - gap * gaps;
        let last = shown.iter().rposition(|s| *s);
        let mut pos = start;
        let mut seen = false;
        for (i, c) in children.iter().enumerate() {
            if shown[i] {
                if seen {
                    pos += gap;
                }
                let l = avail * c.weight / total;
                self.place(c.node, with_span(r, axis, pos, l), gap, vis, out);
                pos += l;
                seen = true;
            } else {
                let between = seen && last.is_some_and(|l| l > i);
                let at = if between { pos + gap / 2.0 } else { pos };
                self.place(c.node, with_span(r, axis, at, 0.0), gap, vis, out);
            }
        }
    }

    fn move_node(&mut self, n: NodeId, dir: Dir, vis: &impl Fn(W) -> bool, enter: bool) -> bool {
        let mut cur = n;
        while let Some((p, i)) = self.position(cur) {
            if self.axis(p) == Some(dir.axis()) {
                let hidden_lane = self
                    .adjacent(p, i, dir)
                    .filter(|&j| enter && !self.visible(self.children(p)[j].node, vis));
                if cur != n {
                    if let Some(j) = hidden_lane {
                        self.join_lane(n, p, j);
                    } else {
                        let at = if dir.forward() { i + 1 } else { i };
                        self.relocate(n, p, at);
                    }
                    return true;
                }
                if let Some(j) = self.next_shown(p, i, dir, vis) {
                    let sib = self.children(p)[j].node;
                    if enter && self.axis(sib).is_some() {
                        let end = self.children(sib).len();
                        self.relocate(n, sib, end);
                    } else {
                        let children = self.children_mut(p);
                        children[i].node = sib;
                        children[j].node = n;
                    }
                    return true;
                }
                if let Some(j) = hidden_lane {
                    self.join_lane(n, p, j);
                    return true;
                }
            }
            cur = p;
        }
        if cur == n || self.axis(cur) == Some(dir.axis()) {
            return false;
        }
        let (old, i) = self.position(n).expect("n is below the root");
        self.unlink(old, i);
        self.normalize(old);
        let r = self.root.expect("the rest of the tree survives");
        if self.axis(r) == Some(dir.axis()) {
            let weight = self.mean_weight(r);
            let at = if dir.forward() {
                self.children(r).len()
            } else {
                0
            };
            self.attach(r, at, n, weight);
        } else {
            let c = self.new_container(dir.axis());
            self.attach(c, 0, r, 1.0);
            let at = if dir.forward() {
                self.children(c).len()
            } else {
                0
            };
            self.attach(c, at, n, 1.0);
            self.root = Some(c);
        }
        true
    }

    fn next_shown(&self, p: NodeId, i: usize, dir: Dir, vis: &impl Fn(W) -> bool) -> Option<usize> {
        let children = self.children(p);
        if dir.forward() {
            (i + 1..children.len()).find(|&j| self.visible(children[j].node, vis))
        } else {
            (0..i).rev().find(|&j| self.visible(children[j].node, vis))
        }
    }

    fn adjacent(&self, p: NodeId, i: usize, dir: Dir) -> Option<usize> {
        let j = if dir.forward() {
            i + 1
        } else {
            i.checked_sub(1)?
        };
        (j < self.children(p).len()).then_some(j)
    }

    /// Moves `n` to the end of the lane at `p`'s child `j`. A lone window
    /// there becomes a lane of its own, perpendicular to `p`.
    fn join_lane(&mut self, n: NodeId, p: NodeId, j: usize) {
        let lane = self.children(p)[j].node;
        let lane = if self.axis(lane).is_some() {
            lane
        } else {
            let c = self.new_container(self.axis(p).expect("p is a container").other());
            self.children_mut(p)[j].node = c;
            self.nodes[c].parent = Some(p);
            if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
                && *expanded == Some(lane)
            {
                *expanded = Some(c);
            }
            self.attach(c, 0, lane, 1.0);
            c
        };
        let end = self.children(lane).len();
        self.relocate(n, lane, end);
    }

    fn relocate(&mut self, n: NodeId, p: NodeId, at: usize) {
        let (old, i) = self.position(n).expect("relocated nodes have a parent");
        let weight = self.mean_weight(p);
        let at = if old == p && i < at { at - 1 } else { at };
        self.unlink(old, i);
        self.attach(p, at, n, weight);
        self.normalize(old);
    }

    /// Places `node` among `p`'s children. A container running along `p`'s
    /// axis is dissolved into `p` so axes keep alternating.
    fn attach(&mut self, p: NodeId, at: usize, node: NodeId, weight: f64) {
        if self.axis(node) == self.axis(p) {
            let Some(Node {
                kind: Kind::Container { children, .. },
                ..
            }) = self.nodes.remove(node)
            else {
                unreachable!("only containers have an axis");
            };
            let total: f64 = children.iter().map(|c| c.weight).sum();
            for (k, c) in children.into_iter().enumerate() {
                self.nodes[c.node].parent = Some(p);
                let weight = weight * c.weight / total;
                self.children_mut(p).insert(
                    at + k,
                    Child {
                        node: c.node,
                        weight,
                    },
                );
            }
        } else {
            self.nodes[node].parent = Some(p);
            self.children_mut(p).insert(at, Child { node, weight });
        }
    }

    fn unlink(&mut self, p: NodeId, i: usize) -> Child {
        let Kind::Container {
            children, expanded, ..
        } = &mut self.nodes[p].kind
        else {
            unreachable!("parents are containers");
        };
        let child = children.remove(i);
        if *expanded == Some(child.node) {
            *expanded = None;
        }
        self.nodes[child.node].parent = None;
        child
    }

    fn detach(&mut self, n: NodeId) {
        match self.position(n) {
            Some((p, i)) => {
                self.unlink(p, i);
                self.normalize(p);
            }
            None => self.root = None,
        }
    }

    /// Repairs a container that lost a child.
    fn normalize(&mut self, c: NodeId) {
        if self.children(c).len() >= 2 {
            return;
        }
        let pos = self.position(c);
        let was_expanded = pos.is_some_and(|(p, _)| self.expanded(p) == Some(c));
        let Some(Node {
            kind: Kind::Container { children, .. },
            ..
        }) = self.nodes.remove(c)
        else {
            unreachable!("only containers are normalized");
        };
        let only = children.into_iter().next();
        match (only, pos) {
            (None, Some((p, i))) => {
                self.unlink_dead(p, i);
                self.normalize(p);
            }
            (None, None) => self.root = None,
            (Some(only), Some((p, i))) => {
                let weight = self.unlink_dead(p, i).weight;
                let leaf_like = self.axis(only.node) != self.axis(p);
                self.attach(p, i, only.node, weight);
                if was_expanded
                    && leaf_like
                    && let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
                {
                    *expanded = Some(only.node);
                }
            }
            (Some(only), None) => {
                self.nodes[only.node].parent = None;
                self.root = Some(only.node);
            }
        }
    }

    /// Like `unlink`, for a child whose node is already gone.
    fn unlink_dead(&mut self, p: NodeId, i: usize) -> Child {
        let Kind::Container {
            children, expanded, ..
        } = &mut self.nodes[p].kind
        else {
            unreachable!("parents are containers");
        };
        let child = children.remove(i);
        if *expanded == Some(child.node) {
            *expanded = None;
        }
        child
    }

    fn new_leaf(&mut self, w: W) -> NodeId {
        let n = self.nodes.insert(Node {
            parent: None,
            kind: Kind::Leaf(w),
        });
        self.leaves.insert(w, n);
        n
    }

    fn new_container(&mut self, axis: Axis) -> NodeId {
        self.nodes.insert(Node {
            parent: None,
            kind: Kind::Container {
                axis,
                children: Vec::new(),
                expanded: None,
            },
        })
    }

    fn position(&self, n: NodeId) -> Option<(NodeId, usize)> {
        let p = self.nodes[n].parent?;
        let i = self.children(p).iter().position(|c| c.node == n)?;
        Some((p, i))
    }

    fn axis(&self, n: NodeId) -> Option<Axis> {
        match &self.nodes[n].kind {
            Kind::Container { axis, .. } => Some(*axis),
            Kind::Leaf(_) => None,
        }
    }

    fn expanded(&self, n: NodeId) -> Option<NodeId> {
        match &self.nodes[n].kind {
            Kind::Container { expanded, .. } => *expanded,
            Kind::Leaf(_) => None,
        }
    }

    fn children(&self, n: NodeId) -> &[Child] {
        match &self.nodes[n].kind {
            Kind::Container { children, .. } => children,
            Kind::Leaf(_) => &[],
        }
    }

    fn children_mut(&mut self, n: NodeId) -> &mut Vec<Child> {
        match &mut self.nodes[n].kind {
            Kind::Container { children, .. } => children,
            Kind::Leaf(_) => unreachable!("leaves have no children"),
        }
    }

    fn mean_weight(&self, p: NodeId) -> f64 {
        let children = self.children(p);
        if children.is_empty() {
            1.0
        } else {
            children.iter().map(|c| c.weight).sum::<f64>() / children.len() as f64
        }
    }

    fn visible(&self, n: NodeId, vis: &impl Fn(W) -> bool) -> bool {
        match &self.nodes[n].kind {
            Kind::Leaf(w) => vis(*w),
            Kind::Container { children, .. } => children.iter().any(|c| self.visible(c.node, vis)),
        }
    }

    #[cfg(test)]
    pub(crate) fn check(&self) {
        let reachable = match self.root {
            Some(r) => {
                assert!(self.nodes[r].parent.is_none());
                self.check_node(r)
            }
            None => 0,
        };
        assert_eq!(reachable, self.nodes.len(), "orphaned nodes");
        for (&w, &n) in &self.leaves {
            assert!(matches!(self.nodes[n].kind, Kind::Leaf(x) if x == w));
        }
    }

    #[cfg(test)]
    fn check_node(&self, n: NodeId) -> usize {
        match &self.nodes[n].kind {
            Kind::Leaf(_) => 1,
            Kind::Container {
                axis,
                children,
                expanded,
            } => {
                assert!(
                    children.len() >= 2,
                    "container with {} children",
                    children.len()
                );
                if let Some(e) = expanded {
                    assert!(children.iter().any(|c| c.node == *e));
                }
                let mut count = 1;
                for c in children {
                    assert!(c.weight > 0.0 && c.weight.is_finite());
                    assert_eq!(self.nodes[c.node].parent, Some(n));
                    assert_ne!(self.axis(c.node), Some(*axis), "axes must alternate");
                    count += self.check_node(c.node);
                }
                count
            }
        }
    }
}

fn span(r: Rect, axis: Axis) -> (f64, f64) {
    match axis {
        Axis::Horizontal => (r.x, r.w),
        Axis::Vertical => (r.y, r.h),
    }
}

fn with_span(r: Rect, axis: Axis, start: f64, len: f64) -> Rect {
    match axis {
        Axis::Horizontal => Rect::new(start, r.y, len, r.h),
        Axis::Vertical => Rect::new(r.x, start, r.w, len),
    }
}

1	use monolith_planner::Rect;
2	use slotmap::{SlotMap, new_key_type};
3	use std::collections::HashMap;
4	use std::hash::Hash;
5
6	new_key_type! { pub struct NodeId; }
7
8	#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
9	pub enum Axis {
10	Horizontal,
11	Vertical,
12	}
13
14	impl Axis {
15	pub fn other(self) -> Self {
16	match self {
17	Self::Horizontal => Self::Vertical,
18	Self::Vertical => Self::Horizontal,
19	}
20	}
21	}
22
23	#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
24	pub enum Dir {
25	Left,
26	Right,
27	Up,
28	Down,
29	}
30
31	impl Dir {
32	pub fn axis(self) -> Axis {
33	match self {
34	Self::Left \| Self::Right => Axis::Horizontal,
35	Self::Up \| Self::Down => Axis::Vertical,
36	}
37	}
38
39	pub fn forward(self) -> bool {
40	matches!(self, Self::Right \| Self::Down)
41	}
42	}
43
44	const MIN_SHARE: f64 = 0.05;
45
46	#[derive(Clone, Debug)]
47	struct Child {
48	node: NodeId,
49	weight: f64,
50	}
51
52	#[derive(Clone, Debug)]
53	enum Kind<W> {
54	Leaf(W),
55	Container {
56	axis: Axis,
57	children: Vec<Child>,
58	expanded: Option<NodeId>,
59	},
60	}
61
62	#[derive(Clone, Debug)]
63	struct Node<W> {
64	parent: Option<NodeId>,
65	kind: Kind<W>,
66	}
67
68	/// One output's tiling tree. Every tiled window of every tag lives here, the
69	/// caller's visibility filter decides which ones take space.
70	///
71	/// Children run on the axis opposite their parent. Containers hold at least
72	/// two children, hidden ones included, and a container left with one child
73	/// is replaced by it.
74	#[derive(Clone, Debug)]
75	pub struct Tree<W> {
76	nodes: SlotMap<NodeId, Node<W>>,
77	root: Option<NodeId>,
78	leaves: HashMap<W, NodeId>,
79	stack: Axis,
80	}
81
82	impl<W: Copy + Eq + Hash> Default for Tree<W> {
83	fn default() -> Self {
84	Self {
85	nodes: SlotMap::with_key(),
86	root: None,
87	leaves: HashMap::new(),
88	stack: Axis::Vertical,
89	}
90	}
91	}
92
93	impl<W: Copy + Eq + Hash> Tree<W> {
94	/// The axis tag rows stack along.
95	pub fn stack_axis(&self) -> Axis {
96	self.stack
97	}
98
99	pub fn contains(&self, w: W) -> bool {
100	self.leaves.contains_key(&w)
101	}
102
103	pub fn is_empty(&self) -> bool {
104	self.root.is_none()
105	}
106
107	pub fn windows(&self) -> impl Iterator<Item = W> + '_ {
108	self.leaves.keys().copied()
109	}
110
111	/// Inserts `w` as the next sibling of `anchor`, or as a new row if
112	/// `anchor` is not in the tree.
113	pub fn insert_after(&mut self, w: W, anchor: W) {
114	let Some(&a) = self.leaves.get(&anchor) else {
115	return self.insert_row(w);
116	};
117	let n = self.new_leaf(w);
118	match self.position(a) {
119	Some((p, i)) if Some(p) == self.root && self.axis(p) == Some(self.stack) => {
120	let weight = self.unlink(p, i).weight;
121	let c = self.new_container(self.stack.other());
122	self.attach(c, 0, a, 1.0);
123	self.attach(c, 1, n, 1.0);
124	self.attach(p, i, c, weight);
125	}
126	Some((p, i)) => {
127	let weight = self.mean_weight(p);
128	self.attach(p, i + 1, n, weight);
129	}
130	None => {
131	let c = self.new_container(self.stack.other());
132	self.attach(c, 0, a, 1.0);
133	self.attach(c, 1, n, 1.0);
134	self.root = Some(c);
135	}
136	}
137	}
138
139	/// Appends `w` as a row of its own along the stacking axis.
140	pub fn insert_row(&mut self, w: W) {
141	let n = self.new_leaf(w);
142	match self.root {
143	None => self.root = Some(n),
144	Some(r) if self.axis(r) == Some(self.stack) => {
145	let weight = self.mean_weight(r);
146	let end = self.children(r).len();
147	self.attach(r, end, n, weight);
148	}
149	Some(r) => {
150	let c = self.new_container(self.stack);
151	self.attach(c, 0, r, 1.0);
152	self.attach(c, 1, n, 1.0);
153	self.root = Some(c);
154	}
155	}
156	}
157
158	pub fn remove(&mut self, w: W) -> bool {
159	let Some(n) = self.leaves.remove(&w) else {
160	return false;
161	};
162	self.detach(n);
163	self.nodes.remove(n);
164	true
165	}
166
167	pub fn retain(&mut self, mut keep: impl FnMut(W) -> bool) {
168	let gone: Vec<W> = self.windows().filter(\|&w\| !keep(w)).collect();
169	for w in gone {
170	self.remove(w);
171	}
172	}
173
174	/// Moves a window one step in `dir`. Leaves swap slots with the next
175	/// visible sibling, enter a sibling container, or step out beside their
176	/// container. Hidden windows never move.
177	pub fn move_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
178	let Some(&n) = self.leaves.get(&w) else {
179	return false;
180	};
181	self.move_node(n, dir, &vis, true)
182	}
183
184	/// Moves the container holding `w` as a rigid block. A window sitting
185	/// directly in the root is its own block.
186	pub fn move_container(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
187	let Some(&n) = self.leaves.get(&w) else {
188	return false;
189	};
190	let block = self.nodes[n]
191	.parent
192	.filter(\|&p\| Some(p) != self.root)
193	.unwrap_or(n);
194	self.move_node(block, dir, &vis, false)
195	}
196
197	/// Moves a window to the end of the next visible lane in `dir`, stepping
198	/// up a level when its container has none that way. A lone window there
199	/// becomes a stack with it.
200	pub fn merge_window(&mut self, w: W, dir: Dir, vis: impl Fn(W) -> bool) -> bool {
201	let Some(&n) = self.leaves.get(&w) else {
202	return false;
203	};
204	let mut cur = n;
205	while let Some((p, i)) = self.position(cur) {
206	if self.axis(p) == Some(dir.axis())
207	&& let Some(j) = self.next_shown(p, i, dir, &vis)
208	{
209	self.join_lane(n, p, j);
210	return true;
211	}
212	cur = p;
213	}
214	false
215	}
216
217	/// Whether every container above `w` is expanded towards it.
218	pub fn maximized(&self, w: W) -> bool {
219	let Some(&leaf) = self.leaves.get(&w) else {
220	return false;
221	};
222	let mut cur = leaf;
223	let mut any = false;
224	while let Some(p) = self.nodes[cur].parent {
225	if self.expanded(p) != Some(cur) {
226	return false;
227	}
228	any = true;
229	cur = p;
230	}
231	any
232	}
233
234	/// Transposes the whole tree.
235	pub fn flip(&mut self) {
236	self.stack = self.stack.other();
237	for node in self.nodes.values_mut() {
238	if let Kind::Container { axis, .. } = &mut node.kind {
239	*axis = axis.other();
240	}
241	}
242	}
243
244	/// Toggles expansion for `count` levels of `w`'s ancestry, starting
245	/// `skip` levels up. Level 0 expands the window inside its container.
246	pub fn toggle_expand(&mut self, w: W, skip: usize, count: usize) -> bool {
247	let Some(&leaf) = self.leaves.get(&w) else {
248	return false;
249	};
250	let mut path = Vec::new();
251	let mut cur = leaf;
252	while let Some(p) = self.nodes[cur].parent {
253	path.push((p, cur));
254	cur = p;
255	}
256	let path: Vec<_> = path.into_iter().skip(skip).take(count).collect();
257	if path.is_empty() {
258	return false;
259	}
260	let all = path.iter().all(\|&(p, c)\| self.expanded(p) == Some(c));
261	for (p, c) in path {
262	if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind {
263	*expanded = (!all).then_some(c);
264	}
265	}
266	true
267	}
268
269	/// Grows `w` by `delta`, a fraction of the visible length of the nearest
270	/// container along `axis` where it has a visible sibling. Hidden siblings
271	/// keep their weights, and with them their share.
272	pub fn resize(&mut self, w: W, axis: Axis, delta: f64, vis: impl Fn(W) -> bool) -> bool {
273	let Some(&leaf) = self.leaves.get(&w) else {
274	return false;
275	};
276	let mut cur = leaf;
277	while let Some((p, i)) = self.position(cur) {
278	if self.axis(p) == Some(axis) {
279	let shown: Vec<usize> = (0..self.children(p).len())
280	.filter(\|&j\| self.visible(self.children(p)[j].node, &vis))
281	.collect();
282	if shown.len() >= 2 {
283	let children = self.children_mut(p);
284	let sum: f64 = shown.iter().map(\|&j\| children[j].weight).sum();
285	let old = children[i].weight;
286	let max = 1.0 - MIN_SHARE * (shown.len() - 1) as f64;
287	let new = (old / sum + delta).clamp(MIN_SHARE, max) * sum;
288	let scale = (sum - new) / (sum - old);
289	for j in shown {
290	children[j].weight = if j == i {
291	new
292	} else {
293	children[j].weight * scale
294	};
295	}
296	return true;
297	}
298	}
299	cur = p;
300	}
301	false
302	}
303
304	/// Lays the tree out in `area`. Hidden windows come back as zero-size
305	/// rects on the boundary where they would reappear.
306	pub fn arrange(&self, area: Rect, gap: f64, vis: impl Fn(W) -> bool) -> Vec<(W, Rect)> {
307	let mut out = Vec::with_capacity(self.leaves.len());
308	if let Some(r) = self.root {
309	let area = if self.visible(r, &vis) {
310	area
311	} else {
312	Rect::new(area.x + area.w / 2.0, area.y, 0.0, area.h)
313	};
314	self.place(r, area, gap, &vis, &mut out);
315	}
316	out
317	}
318
319	fn place(
320	&self,
321	n: NodeId,
322	r: Rect,
323	gap: f64,
324	vis: &impl Fn(W) -> bool,
325	out: &mut Vec<(W, Rect)>,
326	) {
327	let (axis, children, expanded) = match &self.nodes[n].kind {
328	Kind::Leaf(w) => return out.push((*w, r)),
329	Kind::Container {
330	axis,
331	children,
332	expanded,
333	} => (axis, children, expanded),
334	};
335	let shown: Vec<bool> = children.iter().map(\|c\| self.visible(c.node, vis)).collect();
336	let (start, len) = span(r, axis);
337	if let Some(e) = expanded.and_then(\|e\| children.iter().position(\|c\| c.node == e))
338	&& shown[e]
339	{
340	for (i, c) in children.iter().enumerate() {
341	let sub = match i.cmp(&e) {
342	std::cmp::Ordering::Equal => r,
343	std::cmp::Ordering::Less => with_span(r, axis, start, 0.0),
344	std::cmp::Ordering::Greater => with_span(r, axis, start + len, 0.0),
345	};
346	self.place(c.node, sub, gap, vis, out);
347	}
348	return;
349	}
350	let count = shown.iter().filter(\|s\| **s).count();
351	let total: f64 = children
352	.iter()
353	.zip(&shown)
354	.filter(\|(_, s)\| **s)
355	.map(\|(c, _)\| c.weight)
356	.sum();
357	let gaps = count.saturating_sub(1) as f64;
358	let gap = if gaps > 0.0 { gap.min(len / gaps) } else { gap };
359	let avail = len - gap * gaps;
360	let last = shown.iter().rposition(\|s\| *s);
361	let mut pos = start;
362	let mut seen = false;
363	for (i, c) in children.iter().enumerate() {
364	if shown[i] {
365	if seen {
366	pos += gap;
367	}
368	let l = avail * c.weight / total;
369	self.place(c.node, with_span(r, axis, pos, l), gap, vis, out);
370	pos += l;
371	seen = true;
372	} else {
373	let between = seen && last.is_some_and(\|l\| l > i);
374	let at = if between { pos + gap / 2.0 } else { pos };
375	self.place(c.node, with_span(r, axis, at, 0.0), gap, vis, out);
376	}
377	}
378	}
379
380	fn move_node(&mut self, n: NodeId, dir: Dir, vis: &impl Fn(W) -> bool, enter: bool) -> bool {
381	let mut cur = n;
382	while let Some((p, i)) = self.position(cur) {
383	if self.axis(p) == Some(dir.axis()) {
384	let hidden_lane = self
385	.adjacent(p, i, dir)
386	.filter(\|&j\| enter && !self.visible(self.children(p)[j].node, vis));
387	if cur != n {
388	if let Some(j) = hidden_lane {
389	self.join_lane(n, p, j);
390	} else {
391	let at = if dir.forward() { i + 1 } else { i };
392	self.relocate(n, p, at);
393	}
394	return true;
395	}
396	if let Some(j) = self.next_shown(p, i, dir, vis) {
397	let sib = self.children(p)[j].node;
398	if enter && self.axis(sib).is_some() {
399	let end = self.children(sib).len();
400	self.relocate(n, sib, end);
401	} else {
402	let children = self.children_mut(p);
403	children[i].node = sib;
404	children[j].node = n;
405	}
406	return true;
407	}
408	if let Some(j) = hidden_lane {
409	self.join_lane(n, p, j);
410	return true;
411	}
412	}
413	cur = p;
414	}
415	if cur == n \|\| self.axis(cur) == Some(dir.axis()) {
416	return false;
417	}
418	let (old, i) = self.position(n).expect("n is below the root");
419	self.unlink(old, i);
420	self.normalize(old);
421	let r = self.root.expect("the rest of the tree survives");
422	if self.axis(r) == Some(dir.axis()) {
423	let weight = self.mean_weight(r);
424	let at = if dir.forward() {
425	self.children(r).len()
426	} else {
427	0
428	};
429	self.attach(r, at, n, weight);
430	} else {
431	let c = self.new_container(dir.axis());
432	self.attach(c, 0, r, 1.0);
433	let at = if dir.forward() {
434	self.children(c).len()
435	} else {
436	0
437	};
438	self.attach(c, at, n, 1.0);
439	self.root = Some(c);
440	}
441	true
442	}
443
444	fn next_shown(&self, p: NodeId, i: usize, dir: Dir, vis: &impl Fn(W) -> bool) -> Option<usize> {
445	let children = self.children(p);
446	if dir.forward() {
447	(i + 1..children.len()).find(\|&j\| self.visible(children[j].node, vis))
448	} else {
449	(0..i).rev().find(\|&j\| self.visible(children[j].node, vis))
450	}
451	}
452
453	fn adjacent(&self, p: NodeId, i: usize, dir: Dir) -> Option<usize> {
454	let j = if dir.forward() {
455	i + 1
456	} else {
457	i.checked_sub(1)?
458	};
459	(j < self.children(p).len()).then_some(j)
460	}
461
462	/// Moves `n` to the end of the lane at `p`'s child `j`. A lone window
463	/// there becomes a lane of its own, perpendicular to `p`.
464	fn join_lane(&mut self, n: NodeId, p: NodeId, j: usize) {
465	let lane = self.children(p)[j].node;
466	let lane = if self.axis(lane).is_some() {
467	lane
468	} else {
469	let c = self.new_container(self.axis(p).expect("p is a container").other());
470	self.children_mut(p)[j].node = c;
471	self.nodes[c].parent = Some(p);
472	if let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
473	&& *expanded == Some(lane)
474	{
475	*expanded = Some(c);
476	}
477	self.attach(c, 0, lane, 1.0);
478	c
479	};
480	let end = self.children(lane).len();
481	self.relocate(n, lane, end);
482	}
483
484	fn relocate(&mut self, n: NodeId, p: NodeId, at: usize) {
485	let (old, i) = self.position(n).expect("relocated nodes have a parent");
486	let weight = self.mean_weight(p);
487	let at = if old == p && i < at { at - 1 } else { at };
488	self.unlink(old, i);
489	self.attach(p, at, n, weight);
490	self.normalize(old);
491	}
492
493	/// Places `node` among `p`'s children. A container running along `p`'s
494	/// axis is dissolved into `p` so axes keep alternating.
495	fn attach(&mut self, p: NodeId, at: usize, node: NodeId, weight: f64) {
496	if self.axis(node) == self.axis(p) {
497	let Some(Node {
498	kind: Kind::Container { children, .. },
499	..
500	}) = self.nodes.remove(node)
501	else {
502	unreachable!("only containers have an axis");
503	};
504	let total: f64 = children.iter().map(\|c\| c.weight).sum();
505	for (k, c) in children.into_iter().enumerate() {
506	self.nodes[c.node].parent = Some(p);
507	let weight = weight * c.weight / total;
508	self.children_mut(p).insert(
509	at + k,
510	Child {
511	node: c.node,
512	weight,
513	},
514	);
515	}
516	} else {
517	self.nodes[node].parent = Some(p);
518	self.children_mut(p).insert(at, Child { node, weight });
519	}
520	}
521
522	fn unlink(&mut self, p: NodeId, i: usize) -> Child {
523	let Kind::Container {
524	children, expanded, ..
525	} = &mut self.nodes[p].kind
526	else {
527	unreachable!("parents are containers");
528	};
529	let child = children.remove(i);
530	if *expanded == Some(child.node) {
531	*expanded = None;
532	}
533	self.nodes[child.node].parent = None;
534	child
535	}
536
537	fn detach(&mut self, n: NodeId) {
538	match self.position(n) {
539	Some((p, i)) => {
540	self.unlink(p, i);
541	self.normalize(p);
542	}
543	None => self.root = None,
544	}
545	}
546
547	/// Repairs a container that lost a child.
548	fn normalize(&mut self, c: NodeId) {
549	if self.children(c).len() >= 2 {
550	return;
551	}
552	let pos = self.position(c);
553	let was_expanded = pos.is_some_and(\|(p, _)\| self.expanded(p) == Some(c));
554	let Some(Node {
555	kind: Kind::Container { children, .. },
556	..
557	}) = self.nodes.remove(c)
558	else {
559	unreachable!("only containers are normalized");
560	};
561	let only = children.into_iter().next();
562	match (only, pos) {
563	(None, Some((p, i))) => {
564	self.unlink_dead(p, i);
565	self.normalize(p);
566	}
567	(None, None) => self.root = None,
568	(Some(only), Some((p, i))) => {
569	let weight = self.unlink_dead(p, i).weight;
570	let leaf_like = self.axis(only.node) != self.axis(p);
571	self.attach(p, i, only.node, weight);
572	if was_expanded
573	&& leaf_like
574	&& let Kind::Container { expanded, .. } = &mut self.nodes[p].kind
575	{
576	*expanded = Some(only.node);
577	}
578	}
579	(Some(only), None) => {
580	self.nodes[only.node].parent = None;
581	self.root = Some(only.node);
582	}
583	}
584	}
585
586	/// Like `unlink`, for a child whose node is already gone.
587	fn unlink_dead(&mut self, p: NodeId, i: usize) -> Child {
588	let Kind::Container {
589	children, expanded, ..
590	} = &mut self.nodes[p].kind
591	else {
592	unreachable!("parents are containers");
593	};
594	let child = children.remove(i);
595	if *expanded == Some(child.node) {
596	*expanded = None;
597	}
598	child
599	}
600
601	fn new_leaf(&mut self, w: W) -> NodeId {
602	let n = self.nodes.insert(Node {
603	parent: None,
604	kind: Kind::Leaf(w),
605	});
606	self.leaves.insert(w, n);
607	n
608	}
609
610	fn new_container(&mut self, axis: Axis) -> NodeId {
611	self.nodes.insert(Node {
612	parent: None,
613	kind: Kind::Container {
614	axis,
615	children: Vec::new(),
616	expanded: None,
617	},
618	})
619	}
620
621	fn position(&self, n: NodeId) -> Option<(NodeId, usize)> {
622	let p = self.nodes[n].parent?;
623	let i = self.children(p).iter().position(\|c\| c.node == n)?;
624	Some((p, i))
625	}
626
627	fn axis(&self, n: NodeId) -> Option<Axis> {
628	match &self.nodes[n].kind {
629	Kind::Container { axis, .. } => Some(*axis),
630	Kind::Leaf(_) => None,
631	}
632	}
633
634	fn expanded(&self, n: NodeId) -> Option<NodeId> {
635	match &self.nodes[n].kind {
636	Kind::Container { expanded, .. } => *expanded,
637	Kind::Leaf(_) => None,
638	}
639	}
640
641	fn children(&self, n: NodeId) -> &[Child] {
642	match &self.nodes[n].kind {
643	Kind::Container { children, .. } => children,
644	Kind::Leaf(_) => &[],
645	}
646	}
647
648	fn children_mut(&mut self, n: NodeId) -> &mut Vec<Child> {
649	match &mut self.nodes[n].kind {
650	Kind::Container { children, .. } => children,
651	Kind::Leaf(_) => unreachable!("leaves have no children"),
652	}
653	}
654
655	fn mean_weight(&self, p: NodeId) -> f64 {
656	let children = self.children(p);
657	if children.is_empty() {
658	1.0
659	} else {
660	children.iter().map(\|c\| c.weight).sum::<f64>() / children.len() as f64
661	}
662	}
663
664	fn visible(&self, n: NodeId, vis: &impl Fn(W) -> bool) -> bool {
665	match &self.nodes[n].kind {
666	Kind::Leaf(w) => vis(*w),
667	Kind::Container { children, .. } => children.iter().any(\|c\| self.visible(c.node, vis)),
668	}
669	}
670
671	#[cfg(test)]
672	pub(crate) fn check(&self) {
673	let reachable = match self.root {
674	Some(r) => {
675	assert!(self.nodes[r].parent.is_none());
676	self.check_node(r)
677	}
678	None => 0,
679	};
680	assert_eq!(reachable, self.nodes.len(), "orphaned nodes");
681	for (&w, &n) in &self.leaves {
682	assert!(matches!(self.nodes[n].kind, Kind::Leaf(x) if x == w));
683	}
684	}
685
686	#[cfg(test)]
687	fn check_node(&self, n: NodeId) -> usize {
688	match &self.nodes[n].kind {
689	Kind::Leaf(_) => 1,
690	Kind::Container {
691	axis,
692	children,
693	expanded,
694	} => {
695	assert!(
696	children.len() >= 2,
697	"container with {} children",
698	children.len()
699	);
700	if let Some(e) = expanded {
701	assert!(children.iter().any(\|c\| c.node == *e));
702	}
703	let mut count = 1;
704	for c in children {
705	assert!(c.weight > 0.0 && c.weight.is_finite());
706	assert_eq!(self.nodes[c.node].parent, Some(n));
707	assert_ne!(self.axis(c.node), Some(*axis), "axes must alternate");
708	count += self.check_node(c.node);
709	}
710	count
711	}
712	}
713	}
714	}
715
716	fn span(r: Rect, axis: Axis) -> (f64, f64) {
717	match axis {
718	Axis::Horizontal => (r.x, r.w),
719	Axis::Vertical => (r.y, r.h),
720	}
721	}
722
723	fn with_span(r: Rect, axis: Axis, start: f64, len: f64) -> Rect {
724	match axis {
725	Axis::Horizontal => Rect::new(start, r.y, len, r.h),
726	Axis::Vertical => Rect::new(r.x, start, r.w, len),
727	}
728	}