typst/src/layout/tree.rs

use super::*;

use std::any::Any;
use std::fmt::{self, Debug, Formatter};

#[cfg(feature = "layout-cache")]
use fxhash::FxHasher64;

/// A tree of layout nodes.
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct LayoutTree {
    /// Runs of pages with the same properties.
    pub runs: Vec<PageRun>,
}

impl LayoutTree {
    /// Layout the tree into a collection of frames.
    pub fn layout(&self, ctx: &mut LayoutContext) -> Vec<Rc<Frame>> {
        self.runs.iter().flat_map(|run| run.layout(ctx)).collect()
    }
}

/// A run of pages that all have the same properties.
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct PageRun {
    /// The size of each page.
    pub size: Size,
    /// The layout node that produces the actual pages (typically a
    /// [`StackNode`]).
    pub child: LayoutNode,
}

impl PageRun {
    /// Layout the page run.
    pub fn layout(&self, ctx: &mut LayoutContext) -> Vec<Rc<Frame>> {
        // When one of the lengths is infinite the page fits its content along
        // that axis.
        let Size { width, height } = self.size;
        let expand = Spec::new(width.is_finite(), height.is_finite());
        let regions = Regions::repeat(self.size, expand);
        self.child.layout(ctx, &regions).into_iter().map(|c| c.item).collect()
    }
}

/// A dynamic layouting node.
pub struct LayoutNode {
    node: Box<dyn Bounds>,
    #[cfg(feature = "layout-cache")]
    hash: u64,
}

impl LayoutNode {
    /// Create a new instance from any node that satisifies the required bounds.
    #[cfg(not(feature = "layout-cache"))]
    pub fn new<T>(node: T) -> Self
    where
        T: Layout + Debug + Clone + Eq + PartialEq + 'static,
    {
        Self { node: Box::new(node) }
    }

    /// Create a new instance from any node that satisifies the required bounds.
    #[cfg(feature = "layout-cache")]
    pub fn new<T>(node: T) -> Self
    where
        T: Layout + Debug + Clone + Eq + PartialEq + Hash + 'static,
    {
        let hash = {
            let mut state = FxHasher64::default();
            node.type_id().hash(&mut state);
            node.hash(&mut state);
            state.finish()
        };

        Self { node: Box::new(node), hash }
    }
}

impl Layout for LayoutNode {
    fn layout(
        &self,
        ctx: &mut LayoutContext,
        regions: &Regions,
    ) -> Vec<Constrained<Rc<Frame>>> {
        #[cfg(not(feature = "layout-cache"))]
        return self.node.layout(ctx, regions);

        #[cfg(feature = "layout-cache")]
        ctx.layouts.get(self.hash, regions).unwrap_or_else(|| {
            ctx.level += 1;
            let frames = self.node.layout(ctx, regions);
            ctx.level -= 1;
            ctx.layouts.insert(self.hash, frames.clone(), ctx.level);
            frames
        })
    }
}

impl Debug for LayoutNode {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        self.node.fmt(f)
    }
}

impl Clone for LayoutNode {
    fn clone(&self) -> Self {
        Self {
            node: self.node.dyn_clone(),
            #[cfg(feature = "layout-cache")]
            hash: self.hash,
        }
    }
}

impl Eq for LayoutNode {}

impl PartialEq for LayoutNode {
    fn eq(&self, other: &Self) -> bool {
        self.node.dyn_eq(other.node.as_ref())
    }
}

#[cfg(feature = "layout-cache")]
impl Hash for LayoutNode {
    fn hash<H: Hasher>(&self, state: &mut H) {
        state.write_u64(self.hash);
    }
}

trait Bounds: Layout + Debug + 'static {
    fn as_any(&self) -> &dyn Any;
    fn dyn_eq(&self, other: &dyn Bounds) -> bool;
    fn dyn_clone(&self) -> Box<dyn Bounds>;
}

impl<T> Bounds for T
where
    T: Layout + Debug + Eq + PartialEq + Clone + 'static,
{
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn dyn_eq(&self, other: &dyn Bounds) -> bool {
        if let Some(other) = other.as_any().downcast_ref::<Self>() {
            self == other
        } else {
            false
        }
    }

    fn dyn_clone(&self) -> Box<dyn Bounds> {
        Box::new(self.clone())
    }
}