typst/src/layout/mod.rs

//! The core layouting engine.

use std::io::{self, Write};
use smallvec::SmallVec;

use toddle::query::{FontClass, SharedFontLoader};

use crate::TypesetResult;
use crate::func::Command;
use crate::size::{Size, Size2D, SizeBox};
use crate::style::{LayoutStyle, TextStyle};
use crate::syntax::{Node, SyntaxTree, FuncCall};

mod actions;
mod tree;
mod flex;
mod stack;
mod text;

/// Different kinds of layouters (fully re-exported).
pub mod layouters {
    pub use super::tree::layout_tree;
    pub use super::flex::{FlexLayouter, FlexContext};
    pub use super::stack::{StackLayouter, StackContext};
    pub use super::text::{layout_text, TextContext};
}

pub use actions::{LayoutAction, LayoutActions};
pub use layouters::*;

/// A collection of layouts.
pub type MultiLayout = Vec<Layout>;

/// A sequence of layouting actions inside a box.
#[derive(Debug, Clone)]
pub struct Layout {
    /// The size of the box.
    pub dimensions: Size2D,
    /// How to align this layout in a parent container.
    pub alignment: LayoutAlignment,
    /// The actions composing this layout.
    pub actions: Vec<LayoutAction>,
}

impl Layout {
    /// Returns a vector with all used font indices.
    pub fn find_used_fonts(&self) -> Vec<usize> {
        let mut fonts = Vec::new();
        for action in &self.actions {
            if let LayoutAction::SetFont(index, _) = action {
                if !fonts.contains(index) {
                    fonts.push(*index);
                }
            }
        }
        fonts
    }
}

/// The general context for layouting.
#[derive(Debug, Clone)]
pub struct LayoutContext<'a, 'p> {
    /// The font loader to retrieve fonts from when typesetting text
    /// using [`layout_text`].
    pub loader: &'a SharedFontLoader<'p>,
    /// The style for pages and text.
    pub style: &'a LayoutStyle,
    /// Whether this layouting process handles the top-level pages.
    pub top_level: bool,
    /// The spaces to layout in.
    pub spaces: LayoutSpaces,
    /// The initial axes along which content is laid out.
    pub axes: LayoutAxes,
    /// The alignment of the finished layout.
    pub alignment: LayoutAlignment,
}

/// A possibly stack-allocated vector of layout spaces.
pub type LayoutSpaces = SmallVec<[LayoutSpace; 2]>;

/// Spacial layouting constraints.
#[derive(Debug, Copy, Clone)]
pub struct LayoutSpace {
    /// The maximum size of the box to layout in.
    pub dimensions: Size2D,
    /// Padding that should be respected on each side.
    pub padding: SizeBox,
    /// Whether to expand the dimensions of the resulting layout to the full
    /// dimensions of this space or to shrink them to fit the content for the
    /// horizontal and vertical axis.
    pub expand: LayoutExpansion,
}

impl LayoutSpace {
    /// The offset from the origin to the start of content, that is,
    /// `(padding.left, padding.top)`.
    pub fn start(&self) -> Size2D {
        Size2D::new(self.padding.left, self.padding.right)
    }

    /// The actually usable area (dimensions minus padding).
    pub fn usable(&self) -> Size2D {
        self.dimensions.unpadded(self.padding)
    }

    /// A layout space without padding and dimensions reduced by the padding.
    pub fn usable_space(&self) -> LayoutSpace {
        LayoutSpace {
            dimensions: self.usable(),
            padding: SizeBox::ZERO,
            expand: LayoutExpansion::new(false, false),
        }
    }
}

/// Whether to fit to content or expand to the space's size.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub struct LayoutExpansion {
    pub horizontal: bool,
    pub vertical: bool,
}

impl LayoutExpansion {
    pub fn new(horizontal: bool, vertical: bool) -> LayoutExpansion {
        LayoutExpansion { horizontal, vertical }
    }
}

/// The axes along which the content is laid out.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub struct LayoutAxes {
    pub primary: Axis,
    pub secondary: Axis,
}

impl LayoutAxes {
    pub fn new(primary: Axis, secondary: Axis) -> LayoutAxes {
        if primary.is_horizontal() == secondary.is_horizontal() {
            panic!("LayoutAxes::new: invalid parallel axes {:?} and {:?}", primary, secondary);
        }

        LayoutAxes { primary, secondary }
    }

    /// Return the specified generic axis.
    pub fn generic(&self, axis: GenericAxisKind) -> Axis {
        match axis {
            GenericAxisKind::Primary => self.primary,
            GenericAxisKind::Secondary => self.secondary,
        }
    }

    /// Return the specified specific axis.
    pub fn specific(&self, axis: SpecificAxisKind) -> Axis {
        self.generic(axis.generic(*self))
    }

    /// Returns the generic axis kind which is the horizontal axis.
    pub fn horizontal(&self) -> GenericAxisKind {
        match self.primary.is_horizontal() {
            true => GenericAxisKind::Primary,
            false => GenericAxisKind::Secondary,
        }
    }

    /// Returns the generic axis kind which is the vertical axis.
    pub fn vertical(&self) -> GenericAxisKind {
        self.horizontal().inv()
    }

    /// Returns the specific axis kind which is the primary axis.
    pub fn primary(&self) -> SpecificAxisKind {
        match self.primary.is_horizontal() {
            true => SpecificAxisKind::Horizontal,
            false => SpecificAxisKind::Vertical,
        }
    }

    /// Returns the specific axis kind which is the secondary axis.
    pub fn secondary(&self) -> SpecificAxisKind {
        self.primary().inv()
    }

    /// Returns the generic alignment corresponding to left-alignment.
    pub fn left(&self) -> Alignment {
        let positive = match self.primary.is_horizontal() {
            true => self.primary.is_positive(),
            false => self.secondary.is_positive(),
        };

        if positive { Alignment::Origin } else { Alignment::End }
    }

    /// Returns the generic alignment corresponding to right-alignment.
    pub fn right(&self) -> Alignment {
        self.left().inv()
    }

    /// Returns the generic alignment corresponding to top-alignment.
    pub fn top(&self) -> Alignment {
        let positive = match self.primary.is_horizontal() {
            true => self.secondary.is_positive(),
            false => self.primary.is_positive(),
        };

        if positive { Alignment::Origin } else { Alignment::End }
    }

    /// Returns the generic alignment corresponding to bottom-alignment.
    pub fn bottom(&self) -> Alignment {
        self.top().inv()
    }
}

impl Default for LayoutAxes {
    fn default() -> LayoutAxes {
        LayoutAxes {
            primary: Axis::LeftToRight,
            secondary: Axis::TopToBottom,
        }
    }
}

/// Directions along which content is laid out.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub enum Axis {
    LeftToRight,
    RightToLeft,
    TopToBottom,
    BottomToTop,
}

impl Axis {
    /// Whether this is a horizontal axis.
    pub fn is_horizontal(&self) -> bool {
        match self {
            Axis::LeftToRight | Axis::RightToLeft => true,
            Axis::TopToBottom | Axis::BottomToTop => false,
        }
    }

    /// Whether this axis points into the positive coordinate direction.
    pub fn is_positive(&self) -> bool {
        match self {
            Axis::LeftToRight | Axis::TopToBottom => true,
            Axis::RightToLeft | Axis::BottomToTop => false,
        }
    }

    /// The inverse axis.
    pub fn inv(&self) -> Axis {
        match self {
            Axis::LeftToRight => Axis::RightToLeft,
            Axis::RightToLeft => Axis::LeftToRight,
            Axis::TopToBottom => Axis::BottomToTop,
            Axis::BottomToTop => Axis::TopToBottom,
        }
    }

    /// The direction factor for this axis.
    ///
    /// - 1 if the axis is positive.
    /// - -1 if the axis is negative.
    pub fn factor(&self) -> i32 {
        if self.is_positive() { 1 } else { -1 }
    }
}

/// The two generic kinds of layouting axes.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub enum GenericAxisKind {
    Primary,
    Secondary,
}

impl GenericAxisKind {
    /// The specific version of this axis in the given system of axes.
    pub fn specific(&self, axes: LayoutAxes) -> SpecificAxisKind {
        match self {
            GenericAxisKind::Primary => axes.primary(),
            GenericAxisKind::Secondary => axes.secondary(),
        }
    }

    /// The other axis.
    pub fn inv(&self) -> GenericAxisKind {
        match self {
            GenericAxisKind::Primary => GenericAxisKind::Secondary,
            GenericAxisKind::Secondary => GenericAxisKind::Primary,
        }
    }
}

/// The two specific kinds of layouting axes.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub enum SpecificAxisKind {
    Horizontal,
    Vertical,
}

impl SpecificAxisKind {
    /// The generic version of this axis in the given system of axes.
    pub fn generic(&self, axes: LayoutAxes) -> GenericAxisKind {
        match self {
            SpecificAxisKind::Horizontal => axes.horizontal(),
            SpecificAxisKind::Vertical => axes.vertical(),
        }
    }

    /// The other axis.
    pub fn inv(&self) -> SpecificAxisKind {
        match self {
            SpecificAxisKind::Horizontal => SpecificAxisKind::Vertical,
            SpecificAxisKind::Vertical => SpecificAxisKind::Horizontal,
        }
    }
}

/// The place to put a layout in a container.
#[derive(Default, Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub struct LayoutAlignment {
    pub primary: Alignment,
    pub secondary: Alignment,
}

impl LayoutAlignment {
    pub fn new(primary: Alignment, secondary: Alignment) -> LayoutAlignment {
        LayoutAlignment { primary, secondary }
    }
}

/// Where to align content.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub enum Alignment {
    Origin,
    Center,
    End,
}

impl Alignment {
    /// The inverse alignment.
    pub fn inv(&self) -> Alignment {
        match self {
            Alignment::Origin => Alignment::End,
            Alignment::Center => Alignment::Center,
            Alignment::End => Alignment::Origin,
        }
    }
}

impl Default for Alignment {
    fn default() -> Alignment {
        Alignment::Origin
    }
}

/// Whitespace between boxes with different interaction properties.
#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub enum SpacingKind {
    /// A hard space consumes surrounding soft spaces and is always layouted.
    Hard,
    /// A soft space consumes surrounding soft spaces with higher value.
    Soft(u32),
}

/// The standard spacing kind used for paragraph spacing.
const PARAGRAPH_KIND: SpacingKind = SpacingKind::Soft(1);

/// The standard spacing kind used for normal spaces between boxes.
const SPACE_KIND: SpacingKind = SpacingKind::Soft(2);

/// The last appeared spacing.
#[derive(Debug, Copy, Clone, PartialEq)]
enum LastSpacing {
    Hard,
    Soft(Size, u32),
    None,
}

impl LastSpacing {
    /// The size of the soft space if this is a soft space or zero otherwise.
    fn soft_or_zero(&self) -> Size {
        match self {
            LastSpacing::Soft(space, _) => *space,
            _ => Size::ZERO,
        }
    }
}

/// Layout components that can be serialized.
pub trait Serialize {
    /// Serialize the data structure into an output writable.
    fn serialize<W: Write>(&self, f: &mut W) -> io::Result<()>;
}

impl Serialize for Layout {
    fn serialize<W: Write>(&self, f: &mut W) -> io::Result<()> {
        writeln!(f, "{:.4} {:.4}", self.dimensions.x.to_pt(), self.dimensions.y.to_pt())?;
        writeln!(f, "{}", self.actions.len())?;
        for action in &self.actions {
            action.serialize(f)?;
            writeln!(f)?;
        }
        Ok(())
    }
}

impl Serialize for MultiLayout {
    fn serialize<W: Write>(&self, f: &mut W) -> io::Result<()> {
        writeln!(f, "{}", self.len())?;
        for layout in self {
            layout.serialize(f)?;
        }
        Ok(())
    }
}

/// The result type for layouting.
pub type LayoutResult<T> = TypesetResult<T>;