cranpose_ui/modifier/

window_root.rs

//! The window root modifier: a node whose subtree is the content of its own
//! window while staying inside the one composition.
//!
//! The node measures its content into the window's size and reports a zero
//! size to its parent, so the parent lays out as if the subtree were absent.
//! It registers itself with the app context's window root registry, which a
//! platform reads after each update to learn which windows exist; the window
//! is identified by the layout node that carries the modifier. The scene
//! builder skips window roots when it builds a parent's scene and starts at
//! one when it builds that window's scene.

use std::{
    any::Any,
    cell::{Cell, RefCell},
    collections::HashMap,
    fmt,
    hash::{Hash, Hasher},
    rc::Rc,
};

use cranpose_core::{Applier, MemoryApplier, NodeId};
use cranpose_foundation::{
    Constraints, DelegatableNode, InvalidationKind, LayoutModifierNode, Measurable, ModifierNode,
    ModifierNodeContext, ModifierNodeElement, NodeCapabilities, NodeState, Size,
};
use cranpose_ui_layout::LayoutModifierMeasureResult;

use super::Modifier;
use crate::{
    render_state::{AppContextId, current_app_context, with_app_context_by_id},
    widgets::nodes::layout_node::LayoutNode,
};

/// What a window root needs from the platform's description of its window:
/// the logical size to lay the content out into, read on every measure so a
/// resize needs no new modifier, and the description itself for the platform
/// to take back.
pub trait WindowRootDescriptor: Any {
    /// The window's content size in logical pixels.
    fn layout_size(&self) -> Size;

    /// The descriptor as `Any`, so the platform that made it can downcast it.
    fn as_any(&self) -> &dyn Any;
}

/// A window root the registry knows about.
#[derive(Clone)]
pub struct WindowRootEntry {
    /// The layout node carrying the window root modifier, which identifies
    /// the window: it stays the same node across recompositions.
    pub node: NodeId,
    /// The platform's description of the window.
    pub descriptor: Rc<dyn WindowRootDescriptor>,
}

impl fmt::Debug for WindowRootEntry {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("WindowRootEntry")
            .field("node", &self.node)
            .finish()
    }
}

/// The window roots attached in an app context, in attach order, with a
/// revision that changes whenever the set changes.
#[derive(Default)]
pub struct WindowRootRegistry {
    entries: RefCell<Vec<WindowRootEntry>>,
    revision: Cell<u64>,
}

impl WindowRootRegistry {
    fn register(&self, entry: WindowRootEntry) {
        let mut entries = self.entries.borrow_mut();
        if let Some(existing) = entries.iter_mut().find(|known| known.node == entry.node) {
            *existing = entry;
        } else {
            entries.push(entry);
        }
        self.bump();
    }

    fn unregister(&self, node: NodeId) {
        let mut entries = self.entries.borrow_mut();
        let before = entries.len();
        entries.retain(|entry| entry.node != node);
        if entries.len() != before {
            self.bump();
        }
    }

    fn bump(&self) {
        self.revision.set(self.revision.get().wrapping_add(1));
    }

    /// Whether no window root is attached.
    pub fn is_empty(&self) -> bool {
        self.entries.borrow().is_empty()
    }

    /// Every attached window root.
    pub fn entries(&self) -> Vec<WindowRootEntry> {
        self.entries.borrow().clone()
    }

    /// Changes whenever a window root attaches, detaches or is updated.
    pub fn revision(&self) -> u64 {
        self.revision.get()
    }
}

/// The window roots attached in the current app context.
pub fn window_roots() -> Vec<WindowRootEntry> {
    current_app_context().map_or_else(Vec::new, |context| context.window_roots().entries())
}

/// The current app context's window root revision; see
/// [`WindowRootRegistry::revision`].
pub fn window_roots_revision() -> u64 {
    current_app_context().map_or(0, |context| context.window_roots().revision())
}

/// Whether `node` is a layout node whose modifier chain carries a window root.
pub fn is_window_root(applier: &mut MemoryApplier, node: NodeId) -> bool {
    applier
        .with_node::<LayoutNode, _>(node, |layout_node| layout_node.is_window_root())
        .unwrap_or(false)
}

/// The window root that owns `node`: the nearest node, `node` included, whose
/// modifier chain carries a window root. `None` when the node belongs to the
/// primary root.
pub fn nearest_window_root(applier: &mut MemoryApplier, node: NodeId) -> Option<NodeId> {
    let mut current = node;
    for _ in 0..100_000 {
        if is_window_root(applier, current) {
            return Some(current);
        }
        current = applier.get_mut(current).ok()?.parent()?;
    }
    None
}

/// Reusable ancestry storage for [`nearest_window_roots_into`].
#[derive(Default)]
pub struct WindowRootRoutingScratch {
    owners: HashMap<NodeId, Option<NodeId>>,
    path: Vec<NodeId>,
}

/// [`nearest_window_root`] for each of `nodes`, in order, with every
/// ancestor looked up at most once. In an app context with no window root
/// attached, every node belongs to the primary root and none is looked up.
pub fn nearest_window_roots(applier: &mut MemoryApplier, nodes: &[NodeId]) -> Vec<Option<NodeId>> {
    let mut output = Vec::new();
    nearest_window_roots_into(
        applier,
        nodes.iter().copied(),
        &mut output,
        &mut WindowRootRoutingScratch::default(),
    );
    output
}

/// Fills `output` with [`nearest_window_roots`] results, reusing its storage
/// and the ancestry cache in `scratch` across batches.
///
/// The cache is cleared for every batch, so changes to window-root modifiers
/// and tree attachment are observed immediately.
///
/// ```
/// use cranpose_core::MemoryApplier;
/// use cranpose_ui::{WindowRootRoutingScratch, nearest_window_roots_into};
///
/// let mut applier = MemoryApplier::new();
/// let mut scratch = WindowRootRoutingScratch::default();
/// let mut owners = Vec::new();
/// nearest_window_roots_into(&mut applier, [], &mut owners, &mut scratch);
/// assert!(owners.is_empty());
/// ```
pub fn nearest_window_roots_into(
    applier: &mut MemoryApplier,
    nodes: impl IntoIterator<Item = NodeId>,
    output: &mut Vec<Option<NodeId>>,
    scratch: &mut WindowRootRoutingScratch,
) {
    let nodes = nodes.into_iter();
    output.clear();
    scratch.owners.clear();
    scratch.path.clear();
    let (lower_bound, upper_bound) = nodes.size_hint();
    if lower_bound == 0 && upper_bound == Some(0) {
        return;
    }
    output.reserve(lower_bound);
    if current_app_context().is_some_and(|context| context.window_roots().is_empty()) {
        output.extend(nodes.map(|_| None));
        return;
    }
    for node in nodes {
        let mut current = node;
        scratch.path.clear();
        let owner = loop {
            if let Some(known) = scratch.owners.get(&current) {
                break *known;
            }
            scratch.path.push(current);
            if is_window_root(applier, current) {
                break Some(current);
            }
            match applier.get_mut(current).ok().and_then(|node| node.parent()) {
                Some(parent) if scratch.path.len() < 100_000 => current = parent,
                _ => break None,
            }
        };
        for visited in scratch.path.drain(..) {
            scratch.owners.insert(visited, owner);
        }
        output.push(owner);
    }
}

/// Node that lays its content out into the window's size. That size is the
/// node's own, for the window's scene; the layout pass reports a zero size
/// to the node's parent.
pub struct WindowRootNode {
    descriptor: Rc<dyn WindowRootDescriptor>,
    node_id: Cell<Option<NodeId>>,
    owner: Cell<Option<AppContextId>>,
    state: NodeState,
}

impl fmt::Debug for WindowRootNode {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("WindowRootNode")
            .field("node_id", &self.node_id.get())
            .finish()
    }
}

impl WindowRootNode {
    /// A window root described by `descriptor`, for a platform node that
    /// delegates its layout and registration here.
    pub fn new(descriptor: Rc<dyn WindowRootDescriptor>) -> Self {
        Self {
            descriptor,
            node_id: Cell::new(None),
            owner: Cell::new(None),
            state: NodeState::new(),
        }
    }

    /// Takes a new description of the window and re-registers the root when
    /// it is attached.
    pub fn set_descriptor(&mut self, descriptor: Rc<dyn WindowRootDescriptor>) {
        self.descriptor = descriptor;
        self.register();
    }

    fn entry(&self, node: NodeId) -> WindowRootEntry {
        WindowRootEntry {
            node,
            descriptor: Rc::clone(&self.descriptor),
        }
    }

    fn register(&self) {
        let Some(node) = self.node_id.get() else {
            return;
        };
        let Some(context) = current_app_context() else {
            log::debug!("window root {node} attached outside an app context");
            return;
        };
        self.owner.set(Some(context.id()));
        context.window_roots().register(self.entry(node));
    }

    fn unregister(&self) {
        let (Some(node), Some(owner)) = (self.node_id.get(), self.owner.take()) else {
            return;
        };
        with_app_context_by_id(owner, |context| context.window_roots().unregister(node));
    }
}

impl DelegatableNode for WindowRootNode {
    fn node_state(&self) -> &NodeState {
        &self.state
    }
}

impl ModifierNode for WindowRootNode {
    fn on_attach(&mut self, context: &mut dyn ModifierNodeContext) {
        self.node_id.set(context.node_id());
        self.register();
        context.invalidate(InvalidationKind::Layout);
    }

    fn on_detach(&mut self) {
        self.unregister();
    }

    fn as_layout_node(&self) -> Option<&dyn LayoutModifierNode> {
        Some(self)
    }

    fn as_layout_node_mut(&mut self) -> Option<&mut dyn LayoutModifierNode> {
        Some(self)
    }
}

impl LayoutModifierNode for WindowRootNode {
    fn measure(
        &self,
        _context: &mut dyn ModifierNodeContext,
        measurable: &dyn Measurable,
        _constraints: Constraints,
    ) -> LayoutModifierMeasureResult {
        let size = self.descriptor.layout_size();
        let size = Size::new(size.width.max(0.0), size.height.max(0.0));
        let _content = measurable.measure(Constraints {
            min_width: 0.0,
            max_width: size.width,
            min_height: 0.0,
            max_height: size.height,
        });
        LayoutModifierMeasureResult::with_size(size)
    }

    fn min_intrinsic_width(
        &self,
        _measurable: &dyn Measurable,
        _height: f32,
        _density: f32,
    ) -> f32 {
        0.0
    }

    fn max_intrinsic_width(
        &self,
        _measurable: &dyn Measurable,
        _height: f32,
        _density: f32,
    ) -> f32 {
        0.0
    }

    fn min_intrinsic_height(
        &self,
        _measurable: &dyn Measurable,
        _width: f32,
        _density: f32,
    ) -> f32 {
        0.0
    }

    fn max_intrinsic_height(
        &self,
        _measurable: &dyn Measurable,
        _width: f32,
        _density: f32,
    ) -> f32 {
        0.0
    }
}

/// Element that creates and updates window root nodes.
#[derive(Clone)]
pub struct WindowRootElement {
    descriptor: Rc<dyn WindowRootDescriptor>,
}

impl WindowRootElement {
    /// A window root described by `descriptor`.
    pub fn new(descriptor: Rc<dyn WindowRootDescriptor>) -> Self {
        Self { descriptor }
    }

    fn descriptor_address(&self) -> usize {
        Rc::as_ptr(&self.descriptor).cast::<()>() as usize
    }
}

impl fmt::Debug for WindowRootElement {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("WindowRootElement").finish()
    }
}

impl PartialEq for WindowRootElement {
    fn eq(&self, other: &Self) -> bool {
        Rc::ptr_eq(&self.descriptor, &other.descriptor)
    }
}

impl Hash for WindowRootElement {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.descriptor_address().hash(state);
    }
}

impl ModifierNodeElement for WindowRootElement {
    type Node = WindowRootNode;

    fn create(&self) -> Self::Node {
        WindowRootNode::new(Rc::clone(&self.descriptor))
    }

    fn update(&self, node: &mut Self::Node) {
        node.set_descriptor(Rc::clone(&self.descriptor));
    }

    fn capabilities(&self) -> NodeCapabilities {
        NodeCapabilities::LAYOUT | NodeCapabilities::WINDOW_ROOT
    }

    fn inspector_name(&self) -> &'static str {
        "windowRoot"
    }
}

impl Modifier {
    /// Makes the node the root of its own window, described by `descriptor`
    /// and identified by the node itself. The subtree is laid out into the
    /// descriptor's size and drawn into that window's scene; the parent sees
    /// a node of zero size and its scene skips the subtree. Platforms wrap
    /// this in a modifier that takes their own window configuration.
    pub fn window_root(self, descriptor: Rc<dyn WindowRootDescriptor>) -> Self {
        self.then(Self::with_element(WindowRootElement::new(descriptor)))
    }
}