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|
//! A retained node tree, painted into a character grid.
//!
//! The same arena glimmer's reconciler expects everywhere else: nodes are
//! integer handles, `create` / `apply-props!` / `append-child!` mutate them,
//! and nothing is drawn until the frame call walks the whole thing at once.
//! Interactions come back as a queue the caller drains, because a jolt closure
//! cannot be a callback down here — identity crosses the boundary instead.
//!
//! This module knows nothing about terminals. It is the data; [`crate::layout`]
//! measures it and [`crate::paint`] draws it.
use std::collections::{HashMap, VecDeque};
/// A prop value: the three types the ABI can carry, which is all glimmer needs.
/// Keywords and colours arrive as strings, numbers as doubles, flags as ints.
#[derive(Clone, Debug, PartialEq)]
pub enum Value {
Str(String),
Num(f64),
Bool(bool),
}
/// What a node renders as.
///
/// An unknown tag is kept rather than refused — it paints as a vertical box, so
/// a component written against a tag this backend has not grown yet still shows
/// its children instead of nothing.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum Tag {
Window,
Box,
Frame,
Scroll,
Overlay,
Label,
Title,
DimLabel,
Button,
CheckButton,
Entry,
Separator,
Spacer,
Listbox,
Progress,
Spinner,
Reaction,
Emoji,
Image,
Unknown(String),
}
impl Default for Tag {
fn default() -> Self {
Self::Unknown(String::new())
}
}
impl Tag {
fn parse(name: &str) -> Self {
match name {
"window" => Self::Window,
"box" | "hbox" | "vbox" => Self::Box,
"frame" => Self::Frame,
"scroll" => Self::Scroll,
"overlay" => Self::Overlay,
"label" => Self::Label,
"title" | "title-2" => Self::Title,
"dim-label" => Self::DimLabel,
"button" => Self::Button,
"checkbutton" | "checkbox" => Self::CheckButton,
"entry" => Self::Entry,
"separator" => Self::Separator,
"spacer" | "gap" => Self::Spacer,
"listbox" => Self::Listbox,
"progress" => Self::Progress,
"spinner" => Self::Spinner,
// The two glyph nodes. A reaction is a pill somebody can press —
// the count of who is on it, and whether you are one of them; an
// emoji is the same glyph with none of that, a character in a
// sentence. Both carry what to draw in `:emoji` rather than in a
// label, which is why an unknown tag painted neither.
"reaction" => Self::Reaction,
"emoji" => Self::Emoji,
// A picture, which a cell grid cannot hold: the painter reserves
// the cells and the terminal draws it over them, where it has the
// protocol for that. See `crate::graphics`.
"image" => Self::Image,
other => Self::Unknown(other.to_owned()),
}
}
/// The canonical name: `hbox` and `vbox` are one node, so both answer
/// `box` and carry their orientation in a prop.
pub fn name(&self) -> &str {
match self {
Self::Window => "window",
Self::Box => "box",
Self::Frame => "frame",
Self::Scroll => "scroll",
Self::Overlay => "overlay",
Self::Label => "label",
Self::Title => "title",
Self::DimLabel => "dim-label",
Self::Button => "button",
Self::CheckButton => "checkbutton",
Self::Entry => "entry",
Self::Separator => "separator",
Self::Spacer => "spacer",
Self::Listbox => "listbox",
Self::Progress => "progress",
Self::Spinner => "spinner",
Self::Reaction => "reaction",
Self::Emoji => "emoji",
Self::Image => "image",
Self::Unknown(name) => name,
}
}
/// Whether the focus ring stops here. A container never takes focus of its
/// own; a control that does nothing with a key does not either.
pub fn focusable(&self) -> bool {
matches!(
self,
Self::Button | Self::CheckButton | Self::Entry | Self::Listbox | Self::Reaction
)
}
}
/// One interaction, waiting to be drained by the caller. Names are glimmer's
/// handler props with the `on-` dropped.
#[derive(Clone, Debug, PartialEq)]
pub struct Event {
pub node: u32,
pub name: &'static str,
pub text: String,
pub num: f64,
}
#[derive(Clone, Debug, Default)]
struct Node {
tag: Tag,
props: Props,
children: Vec<u32>,
/// When this node or anything under it last changed. A size measured of
/// this subtree is good for exactly as long as this number holds still,
/// which is what lets one outlive the frame it was taken in.
rev: u64,
/// 0 when unparented. The root's parent is 0 as well, which is what stops
/// the ancestor walk in [`Tree::would_cycle`].
parent: u32,
}
/// A node's props.
///
/// Reading them through this rather than the map means a missing prop and a
/// prop of the wrong type answer the same thing: the default. Nothing a caller
/// can write should be able to make a widget vanish.
#[derive(Clone, Debug, Default)]
pub struct Props(pub HashMap<String, Value>);
impl Props {
pub fn str(&self, key: &str) -> &str {
match self.0.get(key) {
Some(Value::Str(s)) => s,
_ => "",
}
}
pub fn num(&self, key: &str, fallback: f64) -> f64 {
match self.0.get(key) {
Some(Value::Num(n)) => *n,
Some(Value::Bool(b)) => {
if *b {
1.0
} else {
0.0
}
}
_ => fallback,
}
}
/// A count of cells. Negative and absurd values are clamped rather than
/// cast, since `as u16` on a negative double is a silent 0 or 65535.
pub fn cells(&self, key: &str, fallback: u16) -> u16 {
match self.0.get(key) {
Some(Value::Num(n)) if n.is_finite() => n.clamp(0.0, u16::MAX as f64) as u16,
_ => fallback,
}
}
pub fn bool(&self, key: &str, fallback: bool) -> bool {
match self.0.get(key) {
Some(Value::Bool(b)) => *b,
Some(Value::Num(n)) => *n != 0.0,
Some(Value::Str(s)) => s == "true",
_ => fallback,
}
}
pub fn has(&self, key: &str) -> bool {
self.0.contains_key(key)
}
/// The text a widget shows. `:label` and `:text` are the same prop to every
/// glimmer backend; whichever the caller wrote is the one that shows.
pub fn label(&self) -> &str {
if self.has("label") {
self.str("label")
} else {
self.str("text")
}
}
}
/// One prop value as EDN. Whole numbers print without a trailing `.0`: every
/// number crossed the boundary as a double, and `{:spacing 8}` reads better
/// than `{:spacing 8.0}`.
fn write_value(value: &Value, out: &mut String) {
match value {
Value::Bool(b) => out.push_str(if *b { "true" } else { "false" }),
Value::Num(n) => {
if n.is_finite() && n.fract() == 0.0 && n.abs() < 1e15 {
out.push_str(&format!("{}", *n as i64));
} else if n.is_finite() {
out.push_str(&format!("{n}"));
} else {
// EDN has no infinity or NaN literal; say nil rather than emit
// something no reader will take.
out.push_str("nil");
}
}
Value::Str(text) => {
out.push('"');
for c in text.chars() {
match c {
'"' => out.push_str("\\\""),
'\\' => out.push_str("\\\\"),
'\n' => out.push_str("\\n"),
'\r' => out.push_str("\\r"),
'\t' => out.push_str("\\t"),
_ => out.push(c),
}
}
out.push('"');
}
}
}
pub struct Tree {
/// Index 0 is never handed out: 0 is "no node" throughout the ABI.
nodes: Vec<Option<Node>>,
free: Vec<u32>,
root: u32,
pending: VecDeque<Event>,
current: Option<Event>,
/// Counts every change to any node. Never read for itself — it is what
/// stamps `Node::rev`, so that two changes are never confused for one.
revision: u64,
}
impl Default for Tree {
fn default() -> Self {
Self::new()
}
}
impl Tree {
pub fn new() -> Self {
let mut tree = Self {
nodes: vec![None],
free: Vec::new(),
root: 0,
pending: VecDeque::new(),
current: None,
revision: 0,
};
tree.root = tree.new_node("window");
tree
}
pub fn root(&self) -> u32 {
self.root
}
fn slot(&self, id: u32) -> Option<&Node> {
self.nodes.get(id as usize).and_then(|n| n.as_ref())
}
/// The one way to a node that can be changed — so it is the one place a
/// change has to be recorded. Handing the caller a `&mut Node` is handing
/// them everything a measurement of it depended on; whether they write to
/// it or not, this is where a cache has to assume they did.
fn slot_mut(&mut self, id: u32) -> Option<&mut Node> {
self.touch(id);
self.nodes.get_mut(id as usize).and_then(|n| n.as_mut())
}
/// Mark `id` and every node above it as changed.
///
/// Upwards, because that is the direction sizes travel: how tall a message
/// is depends on its own words, and how tall the backlog is depends on the
/// message — so a word typed into one line makes every ancestor's measured
/// size a lie, and no sibling's. Walking the parents is what keeps a new
/// message at the bottom of a long backlog from throwing away the
/// measurements of the hundred above it that did not move.
fn touch(&mut self, id: u32) {
self.revision = self.revision.wrapping_add(1);
let now = self.revision;
let mut at = id;
// Bounded by the depth of the tree, and by the node count besides: a
// parent chain cannot revisit a node, since `would_cycle` is what stops
// one being built.
while at != 0 {
match self.nodes.get_mut(at as usize).and_then(|n| n.as_mut()) {
Some(node) => {
node.rev = now;
at = node.parent;
}
None => break,
}
}
}
/// When this node's subtree last changed. A measurement of it taken at the
/// same number is still the right answer.
pub fn revision_of(&self, id: u32) -> u64 {
self.slot(id).map_or(0, |n| n.rev)
}
pub fn exists(&self, id: u32) -> bool {
self.slot(id).is_some()
}
pub fn new_node(&mut self, tag: &str) -> u32 {
self.revision = self.revision.wrapping_add(1);
let node = Node {
tag: Tag::parse(tag),
rev: self.revision,
..Node::default()
};
match self.free.pop() {
Some(id) => {
self.nodes[id as usize] = Some(node);
id
}
None => {
self.nodes.push(Some(node));
(self.nodes.len() - 1) as u32
}
}
}
/// Free `id` and everything under it. The root is refused: the window node
/// is the one thing a caller cannot drop out from under itself.
pub fn free_node(&mut self, id: u32) {
if id == self.root || !self.exists(id) {
return;
}
let parent = self.slot(id).map(|n| n.parent).unwrap_or(0);
if parent != 0 {
if let Some(node) = self.slot_mut(parent) {
node.children.retain(|c| *c != id);
}
}
self.free_subtree(id);
}
fn free_subtree(&mut self, id: u32) {
let children = self
.slot(id)
.map(|n| n.children.clone())
.unwrap_or_default();
for child in children {
self.free_subtree(child);
}
if self.nodes[id as usize].take().is_some() {
self.revision = self.revision.wrapping_add(1);
self.free.push(id);
}
// An event queued against a node that has since gone would be routed to
// a handler the reconciler has already dropped. Drop it here instead.
self.pending.retain(|e| e.node != id);
}
/// Whether making `child` a child of `parent` would make a loop — `child`
/// being `parent` or one of its ancestors.
fn would_cycle(&self, parent: u32, child: u32) -> bool {
let mut at = parent;
while at != 0 {
if at == child {
return true;
}
at = match self.slot(at) {
Some(node) => node.parent,
None => return false,
};
}
false
}
fn unparent(&mut self, child: u32) {
let parent = self.slot(child).map(|n| n.parent).unwrap_or(0);
if parent != 0 {
if let Some(node) = self.slot_mut(parent) {
node.children.retain(|c| *c != child);
}
}
if let Some(node) = self.slot_mut(child) {
node.parent = 0;
}
}
pub fn append(&mut self, parent: u32, child: u32) -> bool {
if !self.exists(parent) || !self.exists(child) || self.would_cycle(parent, child) {
return false;
}
self.unparent(child);
self.slot_mut(parent).unwrap().children.push(child);
self.slot_mut(child).unwrap().parent = parent;
true
}
/// Unparent *and* free `child`, which is what the reconciler means by
/// remove: a node it has taken out of the tree is a node it has dropped.
pub fn remove(&mut self, parent: u32, child: u32) {
if self.slot(child).map(|n| n.parent) == Some(parent) {
self.free_node(child);
}
}
/// Move `child` after `sibling`; `sibling` 0 means the first position.
pub fn insert_after(&mut self, parent: u32, child: u32, sibling: u32) -> bool {
if !self.exists(parent) || !self.exists(child) || self.would_cycle(parent, child) {
return false;
}
if sibling != 0 && self.slot(sibling).map(|n| n.parent) != Some(parent) {
return false;
}
self.unparent(child);
let at = match sibling {
0 => 0,
_ => {
let children = &self.slot(parent).unwrap().children;
children
.iter()
.position(|c| *c == sibling)
.map_or(0, |i| i + 1)
}
};
self.slot_mut(parent).unwrap().children.insert(at, child);
self.slot_mut(child).unwrap().parent = parent;
true
}
/// Put `new` where `old` was, and free `old`.
pub fn replace(&mut self, parent: u32, old: u32, new: u32) -> bool {
if self.slot(old).map(|n| n.parent) != Some(parent) || !self.exists(new) {
return false;
}
if self.would_cycle(parent, new) {
return false;
}
self.unparent(new);
let at = self
.slot(parent)
.and_then(|n| n.children.iter().position(|c| *c == old));
let Some(at) = at else { return false };
self.slot_mut(parent).unwrap().children[at] = new;
self.slot_mut(new).unwrap().parent = parent;
if let Some(node) = self.slot_mut(old) {
node.parent = 0;
}
self.free_subtree(old);
true
}
// ── reading it back ─────────────────────────────────────────────────────
pub fn tag(&self, id: u32) -> Tag {
self.slot(id).map(|n| n.tag.clone()).unwrap_or_default()
}
pub fn tag_name(&self, id: u32) -> &str {
self.slot(id).map_or("", |n| n.tag.name())
}
pub fn children(&self, id: u32) -> Vec<u32> {
self.slot(id)
.map(|n| n.children.clone())
.unwrap_or_default()
}
pub fn child_count(&self, id: u32) -> usize {
self.slot(id).map_or(0, |n| n.children.len())
}
pub fn child_at(&self, id: u32, index: usize) -> u32 {
self.slot(id)
.and_then(|n| n.children.get(index).copied())
.unwrap_or(0)
}
pub fn parent(&self, id: u32) -> u32 {
self.slot(id).map_or(0, |n| n.parent)
}
/// A node's props, borrowed. A node that is not there lends the empty set,
/// which reads as every default — the same answer `props` has always given
/// for a missing node, without the copy.
///
/// The copying `props` below is what a caller that needs to keep them past
/// the borrow uses. Measuring and painting do not: they read a handful of
/// values and are done, and cloning a whole map per node per question was
/// most of what a frame cost.
pub fn props_of(&self, id: u32) -> &Props {
static NONE: std::sync::OnceLock<Props> = std::sync::OnceLock::new();
match self.slot(id) {
Some(node) => &node.props,
None => NONE.get_or_init(Props::default),
}
}
/// A node's tag, borrowed. `Tag::Unknown` carries the name it was given,
/// so `tag` is a string copy per call where this is a look.
pub fn tag_of(&self, id: u32) -> &Tag {
static NONE: std::sync::OnceLock<Tag> = std::sync::OnceLock::new();
match self.slot(id) {
Some(node) => &node.tag,
None => NONE.get_or_init(Tag::default),
}
}
/// A node's children, borrowed.
pub fn children_of(&self, id: u32) -> &[u32] {
self.slot(id).map_or(&[], |n| n.children.as_slice())
}
pub fn props(&self, id: u32) -> Props {
self.props_of(id).clone()
}
pub fn set(&mut self, id: u32, key: &str, value: Value) {
if let Some(node) = self.slot_mut(id) {
node.props.0.insert(key.to_owned(), value);
}
}
pub fn clear_props(&mut self, id: u32) {
if let Some(node) = self.slot_mut(id) {
node.props.0.clear();
}
}
pub fn get(&self, id: u32, key: &str) -> Option<&Value> {
self.slot(id).and_then(|n| n.props.0.get(key))
}
/// The subtree at `id` as pretty-printed hiccup — what the tree *is*, read
/// back from the arena, rather than what a component meant to build.
///
/// Props are sorted, so two dumps of the same tree compare as text.
pub fn dump(&self, id: u32) -> String {
let mut out = String::new();
self.dump_into(id, 0, &mut out);
out
}
fn dump_into(&self, id: u32, depth: usize, out: &mut String) {
let Some(node) = self.slot(id) else {
out.push_str("nil");
return;
};
let indent = " ".repeat(depth);
out.push_str("[:");
out.push_str(node.tag.name());
let mut keys: Vec<&String> = node.props.0.keys().collect();
keys.sort();
out.push_str(" {");
for (i, key) in keys.iter().enumerate() {
if i > 0 {
out.push(' ');
}
out.push(':');
out.push_str(key);
out.push(' ');
write_value(&node.props.0[*key], out);
}
out.push('}');
for child in &node.children {
out.push('\n');
out.push_str(&indent);
out.push_str(" ");
self.dump_into(*child, depth + 1, out);
}
out.push(']');
}
// ── events ──────────────────────────────────────────────────────────────
pub fn emit(&mut self, node: u32, name: &'static str, text: String, num: f64) {
self.pending.push_back(Event {
node,
name,
text,
num,
});
}
/// Dequeue one event into the accessor slot. False when the queue is empty.
pub fn poll(&mut self) -> bool {
self.current = self.pending.pop_front();
self.current.is_some()
}
pub fn current(&self) -> Option<&Event> {
self.current.as_ref()
}
}
#[cfg(test)]
mod tests {
use super::*;
fn tree_with_button() -> (Tree, u32) {
let mut tree = Tree::new();
let button = tree.new_node("button");
tree.set(button, "label", Value::Str("go".into()));
let root = tree.root();
tree.append(root, button);
(tree, button)
}
#[test]
fn a_dump_is_the_tree_as_hiccup_with_sorted_props() {
let (mut tree, button) = tree_with_button();
tree.set(button, "kind", Value::Str("primary".into()));
assert_eq!(
tree.dump(tree.root()),
"[:window {}\n [:button {:kind \"primary\" :label \"go\"}]]"
);
}
#[test]
fn hbox_and_vbox_are_one_node() {
let mut tree = Tree::new();
let h = tree.new_node("hbox");
let v = tree.new_node("vbox");
assert_eq!(tree.tag_name(h), "box");
assert_eq!(tree.tag_name(v), "box");
}
#[test]
fn an_unknown_tag_keeps_its_name() {
let mut tree = Tree::new();
let node = tree.new_node("sparkline");
assert_eq!(tree.tag_name(node), "sparkline");
assert_eq!(tree.tag(node), Tag::Unknown("sparkline".into()));
}
#[test]
fn removing_a_node_frees_its_subtree_and_reuses_the_handles() {
let mut tree = Tree::new();
let outer = tree.new_node("vbox");
let inner = tree.new_node("label");
tree.append(outer, inner);
tree.append(tree.root(), outer);
tree.remove(tree.root(), outer);
assert!(!tree.exists(outer));
assert!(!tree.exists(inner));
assert_eq!(tree.child_count(tree.root()), 0);
// The arena hands the slots back out rather than growing forever.
assert!([outer, inner].contains(&tree.new_node("label")));
}
#[test]
fn a_node_cannot_become_its_own_ancestor() {
let mut tree = Tree::new();
let outer = tree.new_node("vbox");
let inner = tree.new_node("vbox");
tree.append(outer, inner);
assert!(!tree.append(inner, outer));
assert_eq!(tree.parent(outer), 0);
}
#[test]
fn insert_after_zero_is_the_first_position() {
let mut tree = Tree::new();
let (a, b, c) = (
tree.new_node("label"),
tree.new_node("label"),
tree.new_node("label"),
);
let root = tree.root();
tree.append(root, a);
tree.append(root, b);
tree.insert_after(root, c, 0);
assert_eq!(tree.children(root), vec![c, a, b]);
tree.insert_after(root, c, a);
assert_eq!(tree.children(root), vec![a, c, b]);
}
#[test]
fn replace_keeps_the_position_and_frees_the_old_node() {
let mut tree = Tree::new();
let root = tree.root();
let (a, b) = (tree.new_node("label"), tree.new_node("label"));
tree.append(root, a);
tree.append(root, b);
let fresh = tree.new_node("button");
assert!(tree.replace(root, a, fresh));
assert_eq!(tree.children(root), vec![fresh, b]);
assert!(!tree.exists(a));
}
#[test]
fn the_root_cannot_be_freed() {
let mut tree = Tree::new();
let root = tree.root();
tree.free_node(root);
assert!(tree.exists(root));
}
#[test]
fn an_event_for_a_freed_node_never_reaches_the_caller() {
let (mut tree, button) = tree_with_button();
tree.emit(button, "click", String::new(), 0.0);
tree.remove(tree.root(), button);
assert!(!tree.poll());
}
#[test]
fn props_of_the_wrong_type_read_as_the_default() {
let mut tree = Tree::new();
let node = tree.new_node("progress");
tree.set(node, "value", Value::Str("lots".into()));
let props = tree.props(node);
assert_eq!(props.num("value", 0.5), 0.5);
assert_eq!(props.cells("width-request", 7), 7);
}
#[test]
fn label_and_text_are_the_same_prop() {
let mut tree = Tree::new();
let node = tree.new_node("label");
tree.set(node, "text", Value::Str("hello".into()));
assert_eq!(tree.props(node).label(), "hello");
tree.set(node, "label", Value::Str("hi".into()));
assert_eq!(tree.props(node).label(), "hi");
}
}
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