1 files changed, 381 insertions, 0 deletions
diff --git a/src/eval/layout.rs b/src/eval/layout.rs
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--- /dev/null
+++ b/src/eval/layout.rs
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+//! Layouting infrastructure.
+
+use std::any::{Any, TypeId};
+use std::fmt::{self, Debug, Formatter};
+use std::hash::Hash;
+use std::sync::Arc;
+
+use crate::diag::TypResult;
+use crate::eval::StyleChain;
+use crate::frame::{Element, Frame, Geometry, Shape, Stroke};
+use crate::geom::{Align, Length, Linear, Paint, Point, Sides, Size, Spec, Transform};
+use crate::library::{AlignNode, PadNode, TransformNode, MOVE};
+use crate::util::Prehashed;
+use crate::Vm;
+
+/// A node that can be layouted into a sequence of regions.
+///
+/// Layout return one frame per used region alongside constraints that define
+/// whether the result is reusable in other regions.
+pub trait Layout {
+    /// Layout the node into the given regions, producing constrained frames.
+    fn layout(
+        &self,
+        vm: &mut Vm,
+        regions: &Regions,
+        styles: StyleChain,
+    ) -> TypResult<Vec<Arc<Frame>>>;
+
+    /// Convert to a packed node.
+    fn pack(self) -> LayoutNode
+    where
+        Self: Debug + Hash + Sized + Sync + Send + 'static,
+    {
+        LayoutNode::new(self)
+    }
+}
+
+/// A sequence of regions to layout into.
+#[derive(Debug, Clone)]
+pub struct Regions {
+    /// The (remaining) size of the first region.
+    pub first: Size,
+    /// The base size for relative sizing.
+    pub base: Size,
+    /// The height of followup regions. The width is the same for all regions.
+    pub backlog: std::vec::IntoIter<Length>,
+    /// The height of the final region that is repeated once the backlog is
+    /// drained. The width is the same for all regions.
+    pub last: Option<Length>,
+    /// Whether nodes should expand to fill the regions instead of shrinking to
+    /// fit the content.
+    pub expand: Spec<bool>,
+}
+
+impl Regions {
+    /// Create a new region sequence with exactly one region.
+    pub fn one(size: Size, base: Size, expand: Spec<bool>) -> Self {
+        Self {
+            first: size,
+            base,
+            backlog: vec![].into_iter(),
+            last: None,
+            expand,
+        }
+    }
+
+    /// Create a new sequence of same-size regions that repeats indefinitely.
+    pub fn repeat(size: Size, base: Size, expand: Spec<bool>) -> Self {
+        Self {
+            first: size,
+            base,
+            backlog: vec![].into_iter(),
+            last: Some(size.y),
+            expand,
+        }
+    }
+
+    /// Create new regions where all sizes are mapped with `f`.
+    ///
+    /// Note that since all regions must have the same width, the width returned
+    /// by `f` is ignored for the backlog and the final region.
+    pub fn map<F>(&self, mut f: F) -> Self
+    where
+        F: FnMut(Size) -> Size,
+    {
+        let x = self.first.x;
+        Self {
+            first: f(self.first),
+            base: f(self.base),
+            backlog: self
+                .backlog
+                .as_slice()
+                .iter()
+                .map(|&y| f(Size::new(x, y)).y)
+                .collect::<Vec<_>>()
+                .into_iter(),
+            last: self.last.map(|y| f(Size::new(x, y)).y),
+            expand: self.expand,
+        }
+    }
+
+    /// Whether the first region is full and a region break is called for.
+    pub fn is_full(&self) -> bool {
+        Length::zero().fits(self.first.y) && !self.in_last()
+    }
+
+    /// Whether the first region is the last usable region.
+    ///
+    /// If this is true, calling `next()` will have no effect.
+    pub fn in_last(&self) -> bool {
+        self.backlog.len() == 0 && self.last.map_or(true, |height| self.first.y == height)
+    }
+
+    /// Advance to the next region if there is any.
+    pub fn next(&mut self) {
+        if let Some(height) = self.backlog.next().or(self.last) {
+            self.first.y = height;
+            self.base.y = height;
+        }
+    }
+
+    /// An iterator that returns the sizes of the first and all following
+    /// regions, equivalently to what would be produced by calling
+    /// [`next()`](Self::next) repeatedly until all regions are exhausted.
+    /// This iterater may be infinite.
+    pub fn iter(&self) -> impl Iterator<Item = Size> + '_ {
+        let first = std::iter::once(self.first);
+        let backlog = self.backlog.as_slice().iter();
+        let last = self.last.iter().cycle();
+        first.chain(backlog.chain(last).map(|&h| Size::new(self.first.x, h)))
+    }
+}
+
+/// A type-erased layouting node with a precomputed hash.
+#[derive(Clone, Hash)]
+pub struct LayoutNode(Arc<Prehashed<dyn Bounds>>);
+
+impl LayoutNode {
+    /// Pack any layoutable node.
+    pub fn new<T>(node: T) -> Self
+    where
+        T: Layout + Debug + Hash + Sync + Send + 'static,
+    {
+        Self(Arc::new(Prehashed::new(node)))
+    }
+
+    /// Check whether the contained node is a specific layout node.
+    pub fn is<T: 'static>(&self) -> bool {
+        self.0.as_any().is::<T>()
+    }
+
+    /// The type id of this node.
+    pub fn id(&self) -> TypeId {
+        self.0.as_any().type_id()
+    }
+
+    /// Try to downcast to a specific layout node.
+    pub fn downcast<T>(&self) -> Option<&T>
+    where
+        T: Layout + Debug + Hash + 'static,
+    {
+        self.0.as_any().downcast_ref()
+    }
+
+    /// Force a size for this node.
+    pub fn sized(self, sizing: Spec<Option<Linear>>) -> Self {
+        if sizing.any(Option::is_some) {
+            SizedNode { sizing, child: self }.pack()
+        } else {
+            self
+        }
+    }
+
+    /// Fill the frames resulting from a node.
+    pub fn filled(self, fill: Paint) -> Self {
+        FillNode { fill, child: self }.pack()
+    }
+
+    /// Stroke the frames resulting from a node.
+    pub fn stroked(self, stroke: Stroke) -> Self {
+        StrokeNode { stroke, child: self }.pack()
+    }
+
+    /// Set alignments for this node.
+    pub fn aligned(self, aligns: Spec<Option<Align>>) -> Self {
+        if aligns.any(Option::is_some) {
+            AlignNode { aligns, child: self }.pack()
+        } else {
+            self
+        }
+    }
+
+    /// Pad this node at the sides.
+    pub fn padded(self, padding: Sides<Linear>) -> Self {
+        if !padding.left.is_zero()
+            || !padding.top.is_zero()
+            || !padding.right.is_zero()
+            || !padding.bottom.is_zero()
+        {
+            PadNode { padding, child: self }.pack()
+        } else {
+            self
+        }
+    }
+
+    /// Transform this node's contents without affecting layout.
+    pub fn moved(self, offset: Point) -> Self {
+        if !offset.is_zero() {
+            TransformNode::<MOVE> {
+                transform: Transform::translation(offset.x, offset.y),
+                child: self,
+            }
+            .pack()
+        } else {
+            self
+        }
+    }
+}
+
+impl Layout for LayoutNode {
+    #[track_caller]
+    fn layout(
+        &self,
+        vm: &mut Vm,
+        regions: &Regions,
+        styles: StyleChain,
+    ) -> TypResult<Vec<Arc<Frame>>> {
+        // TODO(query)
+        self.0.layout(vm, regions, styles.barred(self.id()))
+    }
+
+    fn pack(self) -> LayoutNode {
+        self
+    }
+}
+
+impl Default for LayoutNode {
+    fn default() -> Self {
+        EmptyNode.pack()
+    }
+}
+
+impl Debug for LayoutNode {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+impl PartialEq for LayoutNode {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.eq(&other.0)
+    }
+}
+
+trait Bounds: Layout + Debug + Sync + Send + 'static {
+    fn as_any(&self) -> &dyn Any;
+}
+
+impl<T> Bounds for T
+where
+    T: Layout + Debug + Hash + Sync + Send + 'static,
+{
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+}
+
+/// A layout node that produces an empty frame.
+///
+/// The packed version of this is returned by [`PackedNode::default`].
+#[derive(Debug, Hash)]
+struct EmptyNode;
+
+impl Layout for EmptyNode {
+    fn layout(
+        &self,
+        _: &mut Vm,
+        regions: &Regions,
+        _: StyleChain,
+    ) -> TypResult<Vec<Arc<Frame>>> {
+        Ok(vec![Arc::new(Frame::new(
+            regions.expand.select(regions.first, Size::zero()),
+        ))])
+    }
+}
+
+/// Fix the size of a node.
+#[derive(Debug, Hash)]
+struct SizedNode {
+    /// How to size the node horizontally and vertically.
+    sizing: Spec<Option<Linear>>,
+    /// The node to be sized.
+    child: LayoutNode,
+}
+
+impl Layout for SizedNode {
+    fn layout(
+        &self,
+        vm: &mut Vm,
+        regions: &Regions,
+        styles: StyleChain,
+    ) -> TypResult<Vec<Arc<Frame>>> {
+        // The "pod" is the region into which the child will be layouted.
+        let pod = {
+            // Resolve the sizing to a concrete size.
+            let size = self
+                .sizing
+                .zip(regions.base)
+                .map(|(s, b)| s.map(|v| v.resolve(b)))
+                .unwrap_or(regions.first);
+
+            // Select the appropriate base and expansion for the child depending
+            // on whether it is automatically or linearly sized.
+            let is_auto = self.sizing.map_is_none();
+            let base = is_auto.select(regions.base, size);
+            let expand = regions.expand | !is_auto;
+
+            Regions::one(size, base, expand)
+        };
+
+        // Layout the child.
+        let mut frames = self.child.layout(vm, &pod, styles)?;
+
+        // Ensure frame size matches regions size if expansion is on.
+        let frame = &mut frames[0];
+        let target = regions.expand.select(regions.first, frame.size);
+        Arc::make_mut(frame).resize(target, Align::LEFT_TOP);
+
+        Ok(frames)
+    }
+}
+
+/// Fill the frames resulting from a node.
+#[derive(Debug, Hash)]
+struct FillNode {
+    /// How to fill the frames resulting from the `child`.
+    fill: Paint,
+    /// The node to fill.
+    child: LayoutNode,
+}
+
+impl Layout for FillNode {
+    fn layout(
+        &self,
+        vm: &mut Vm,
+        regions: &Regions,
+        styles: StyleChain,
+    ) -> TypResult<Vec<Arc<Frame>>> {
+        let mut frames = self.child.layout(vm, regions, styles)?;
+        for frame in &mut frames {
+            let shape = Shape::filled(Geometry::Rect(frame.size), self.fill);
+            Arc::make_mut(frame).prepend(Point::zero(), Element::Shape(shape));
+        }
+        Ok(frames)
+    }
+}
+
+/// Stroke the frames resulting from a node.
+#[derive(Debug, Hash)]
+struct StrokeNode {
+    /// How to stroke the frames resulting from the `child`.
+    stroke: Stroke,
+    /// The node to stroke.
+    child: LayoutNode,
+}
+
+impl Layout for StrokeNode {
+    fn layout(
+        &self,
+        vm: &mut Vm,
+        regions: &Regions,
+        styles: StyleChain,
+    ) -> TypResult<Vec<Arc<Frame>>> {
+        let mut frames = self.child.layout(vm, regions, styles)?;
+        for frame in &mut frames {
+            let shape = Shape::stroked(Geometry::Rect(frame.size), self.stroke);
+            Arc::make_mut(frame).prepend(Point::zero(), Element::Shape(shape));
+        }
+        Ok(frames)
+    }
+}