1 files changed, 207 insertions, 0 deletions
diff --git a/crates/typst-layout/src/math/shared.rs b/crates/typst-layout/src/math/shared.rs
new file mode 100644
index 00000000..13477c10
--- /dev/null
+++ b/crates/typst-layout/src/math/shared.rs
@@ -0,0 +1,207 @@
+use ttf_parser::math::MathValue;
+use typst_library::foundations::{Style, StyleChain};
+use typst_library::layout::{Abs, Em, FixedAlignment, Frame, Point, Size, VAlignment};
+use typst_library::math::{EquationElem, MathSize};
+use typst_library::text::TextElem;
+use typst_utils::LazyHash;
+
+use super::{LeftRightAlternator, MathContext, MathFragment, MathRun};
+
+macro_rules! scaled {
+    ($ctx:expr, $styles:expr, text: $text:ident, display: $display:ident $(,)?) => {
+        match typst_library::math::EquationElem::size_in($styles) {
+            typst_library::math::MathSize::Display => scaled!($ctx, $styles, $display),
+            _ => scaled!($ctx, $styles, $text),
+        }
+    };
+    ($ctx:expr, $styles:expr, $name:ident) => {
+        $crate::math::Scaled::scaled(
+            $ctx.constants.$name(),
+            $ctx,
+            $crate::math::scaled_font_size($ctx, $styles),
+        )
+    };
+}
+
+macro_rules! percent {
+    ($ctx:expr, $name:ident) => {
+        $ctx.constants.$name() as f64 / 100.0
+    };
+}
+
+/// How much less high scaled delimiters can be than what they wrap.
+pub const DELIM_SHORT_FALL: Em = Em::new(0.1);
+
+/// Converts some unit to an absolute length with the current font & font size.
+pub trait Scaled {
+    fn scaled(self, ctx: &MathContext, font_size: Abs) -> Abs;
+}
+
+impl Scaled for i16 {
+    fn scaled(self, ctx: &MathContext, font_size: Abs) -> Abs {
+        ctx.font.to_em(self).at(font_size)
+    }
+}
+
+impl Scaled for u16 {
+    fn scaled(self, ctx: &MathContext, font_size: Abs) -> Abs {
+        ctx.font.to_em(self).at(font_size)
+    }
+}
+
+impl Scaled for MathValue<'_> {
+    fn scaled(self, ctx: &MathContext, font_size: Abs) -> Abs {
+        self.value.scaled(ctx, font_size)
+    }
+}
+
+/// Get the font size scaled with the `MathSize`.
+pub fn scaled_font_size(ctx: &MathContext, styles: StyleChain) -> Abs {
+    let factor = match EquationElem::size_in(styles) {
+        MathSize::Display | MathSize::Text => 1.0,
+        MathSize::Script => percent!(ctx, script_percent_scale_down),
+        MathSize::ScriptScript => percent!(ctx, script_script_percent_scale_down),
+    };
+    factor * TextElem::size_in(styles)
+}
+
+/// Styles something as cramped.
+pub fn style_cramped() -> LazyHash<Style> {
+    EquationElem::set_cramped(true).wrap()
+}
+
+/// The style for subscripts in the current style.
+pub fn style_for_subscript(styles: StyleChain) -> [LazyHash<Style>; 2] {
+    [style_for_superscript(styles), EquationElem::set_cramped(true).wrap()]
+}
+
+/// The style for superscripts in the current style.
+pub fn style_for_superscript(styles: StyleChain) -> LazyHash<Style> {
+    EquationElem::set_size(match EquationElem::size_in(styles) {
+        MathSize::Display | MathSize::Text => MathSize::Script,
+        MathSize::Script | MathSize::ScriptScript => MathSize::ScriptScript,
+    })
+    .wrap()
+}
+
+/// The style for numerators in the current style.
+pub fn style_for_numerator(styles: StyleChain) -> LazyHash<Style> {
+    EquationElem::set_size(match EquationElem::size_in(styles) {
+        MathSize::Display => MathSize::Text,
+        MathSize::Text => MathSize::Script,
+        MathSize::Script | MathSize::ScriptScript => MathSize::ScriptScript,
+    })
+    .wrap()
+}
+
+/// The style for denominators in the current style.
+pub fn style_for_denominator(styles: StyleChain) -> [LazyHash<Style>; 2] {
+    [style_for_numerator(styles), EquationElem::set_cramped(true).wrap()]
+}
+
+/// How a delimieter should be aligned when scaling.
+pub fn delimiter_alignment(delimiter: char) -> VAlignment {
+    match delimiter {
+        '⌜' | '⌝' => VAlignment::Top,
+        '⌞' | '⌟' => VAlignment::Bottom,
+        _ => VAlignment::Horizon,
+    }
+}
+
+/// Stack rows on top of each other.
+///
+/// Add a `gap` between each row and uses the baseline of the `baseline`-th
+/// row for the whole frame. `alternator` controls the left/right alternating
+/// alignment behavior of `AlignPointElem` in the rows.
+pub fn stack(
+    rows: Vec<MathRun>,
+    align: FixedAlignment,
+    gap: Abs,
+    baseline: usize,
+    alternator: LeftRightAlternator,
+    minimum_ascent_descent: Option<(Abs, Abs)>,
+) -> Frame {
+    let rows: Vec<_> = rows.into_iter().flat_map(|r| r.rows()).collect();
+    let AlignmentResult { points, width } = alignments(&rows);
+    let rows: Vec<_> = rows
+        .into_iter()
+        .map(|row| row.into_line_frame(&points, alternator))
+        .collect();
+
+    let padded_height = |height: Abs| {
+        height.max(minimum_ascent_descent.map_or(Abs::zero(), |(a, d)| a + d))
+    };
+
+    let mut frame = Frame::soft(Size::new(
+        width,
+        rows.iter().map(|row| padded_height(row.height())).sum::<Abs>()
+            + rows.len().saturating_sub(1) as f64 * gap,
+    ));
+
+    let mut y = Abs::zero();
+    for (i, row) in rows.into_iter().enumerate() {
+        let x = if points.is_empty() {
+            align.position(width - row.width())
+        } else {
+            Abs::zero()
+        };
+        let ascent_padded_part = minimum_ascent_descent
+            .map_or(Abs::zero(), |(a, _)| (a - row.ascent()))
+            .max(Abs::zero());
+        let pos = Point::new(x, y + ascent_padded_part);
+        if i == baseline {
+            frame.set_baseline(y + row.baseline() + ascent_padded_part);
+        }
+        y += padded_height(row.height()) + gap;
+        frame.push_frame(pos, row);
+    }
+
+    frame
+}
+
+/// Determine the positions of the alignment points, according to the input rows combined.
+pub fn alignments(rows: &[MathRun]) -> AlignmentResult {
+    let mut widths = Vec::<Abs>::new();
+
+    let mut pending_width = Abs::zero();
+    for row in rows {
+        let mut width = Abs::zero();
+        let mut alignment_index = 0;
+
+        for fragment in row.iter() {
+            if matches!(fragment, MathFragment::Align) {
+                if alignment_index < widths.len() {
+                    widths[alignment_index].set_max(width);
+                } else {
+                    widths.push(width.max(pending_width));
+                }
+                width = Abs::zero();
+                alignment_index += 1;
+            } else {
+                width += fragment.width();
+            }
+        }
+        if widths.is_empty() {
+            pending_width.set_max(width);
+        } else if alignment_index < widths.len() {
+            widths[alignment_index].set_max(width);
+        } else {
+            widths.push(width.max(pending_width));
+        }
+    }
+
+    let mut points = widths;
+    for i in 1..points.len() {
+        let prev = points[i - 1];
+        points[i] += prev;
+    }
+    AlignmentResult {
+        width: points.last().copied().unwrap_or(pending_width),
+        points,
+    }
+}
+
+pub struct AlignmentResult {
+    pub points: Vec<Abs>,
+    pub width: Abs,
+}