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-rw-r--r--crates/typst-layout/src/math/attach.rs515
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diff --git a/crates/typst-layout/src/math/attach.rs b/crates/typst-layout/src/math/attach.rs
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+use typst_library::diag::SourceResult;
+use typst_library::foundations::{Packed, Smart, StyleChain};
+use typst_library::layout::{Abs, Axis, Corner, Frame, Length, Point, Rel, Size};
+use typst_library::math::{
+ AttachElem, EquationElem, LimitsElem, PrimesElem, ScriptsElem, StretchElem,
+};
+use typst_library::text::TextElem;
+use typst_utils::OptionExt;
+
+use super::{
+ stretch_fragment, style_for_subscript, style_for_superscript, FrameFragment, Limits,
+ MathContext, MathFragment,
+};
+
+macro_rules! measure {
+ ($e: ident, $attr: ident) => {
+ $e.as_ref().map(|e| e.$attr()).unwrap_or_default()
+ };
+}
+
+/// Lays out an [`AttachElem`].
+#[typst_macros::time(name = "math.attach", span = elem.span())]
+pub fn layout_attach(
+ elem: &Packed<AttachElem>,
+ ctx: &mut MathContext,
+ styles: StyleChain,
+) -> SourceResult<()> {
+ let merged = elem.merge_base();
+ let elem = merged.as_ref().unwrap_or(elem);
+ let stretch = stretch_size(styles, elem);
+
+ let mut base = ctx.layout_into_fragment(elem.base(), styles)?;
+ let sup_style = style_for_superscript(styles);
+ let sup_style_chain = styles.chain(&sup_style);
+ let tl = elem.tl(sup_style_chain);
+ let tr = elem.tr(sup_style_chain);
+ let primed = tr.as_ref().is_some_and(|content| content.is::<PrimesElem>());
+ let t = elem.t(sup_style_chain);
+
+ let sub_style = style_for_subscript(styles);
+ let sub_style_chain = styles.chain(&sub_style);
+ let bl = elem.bl(sub_style_chain);
+ let br = elem.br(sub_style_chain);
+ let b = elem.b(sub_style_chain);
+
+ let limits = base.limits().active(styles);
+ let (t, tr) = match (t, tr) {
+ (Some(t), Some(tr)) if primed && !limits => (None, Some(tr + t)),
+ (Some(t), None) if !limits => (None, Some(t)),
+ (t, tr) => (t, tr),
+ };
+ let (b, br) = if limits || br.is_some() { (b, br) } else { (None, b) };
+
+ macro_rules! layout {
+ ($content:ident, $style_chain:ident) => {
+ $content
+ .map(|elem| ctx.layout_into_fragment(&elem, $style_chain))
+ .transpose()
+ };
+ }
+
+ // Layout the top and bottom attachments early so we can measure their
+ // widths, in order to calculate what the stretch size is relative to.
+ let t = layout!(t, sup_style_chain)?;
+ let b = layout!(b, sub_style_chain)?;
+ if let Some(stretch) = stretch {
+ let relative_to_width = measure!(t, width).max(measure!(b, width));
+ stretch_fragment(
+ ctx,
+ styles,
+ &mut base,
+ Some(Axis::X),
+ Some(relative_to_width),
+ stretch,
+ Abs::zero(),
+ );
+ }
+
+ let fragments = [
+ layout!(tl, sup_style_chain)?,
+ t,
+ layout!(tr, sup_style_chain)?,
+ layout!(bl, sub_style_chain)?,
+ b,
+ layout!(br, sub_style_chain)?,
+ ];
+
+ layout_attachments(ctx, styles, base, fragments)
+}
+
+/// Lays out a [`PrimeElem`].
+#[typst_macros::time(name = "math.primes", span = elem.span())]
+pub fn layout_primes(
+ elem: &Packed<PrimesElem>,
+ ctx: &mut MathContext,
+ styles: StyleChain,
+) -> SourceResult<()> {
+ match *elem.count() {
+ count @ 1..=4 => {
+ let c = match count {
+ 1 => '′',
+ 2 => '″',
+ 3 => '‴',
+ 4 => '⁗',
+ _ => unreachable!(),
+ };
+ let f = ctx.layout_into_fragment(&TextElem::packed(c), styles)?;
+ ctx.push(f);
+ }
+ count => {
+ // Custom amount of primes
+ let prime =
+ ctx.layout_into_fragment(&TextElem::packed('′'), styles)?.into_frame();
+ let width = prime.width() * (count + 1) as f64 / 2.0;
+ let mut frame = Frame::soft(Size::new(width, prime.height()));
+ frame.set_baseline(prime.ascent());
+
+ for i in 0..count {
+ frame.push_frame(
+ Point::new(prime.width() * (i as f64 / 2.0), Abs::zero()),
+ prime.clone(),
+ )
+ }
+ ctx.push(FrameFragment::new(ctx, styles, frame).with_text_like(true));
+ }
+ }
+ Ok(())
+}
+
+/// Lays out a [`ScriptsElem`].
+#[typst_macros::time(name = "math.scripts", span = elem.span())]
+pub fn layout_scripts(
+ elem: &Packed<ScriptsElem>,
+ ctx: &mut MathContext,
+ styles: StyleChain,
+) -> SourceResult<()> {
+ let mut fragment = ctx.layout_into_fragment(elem.body(), styles)?;
+ fragment.set_limits(Limits::Never);
+ ctx.push(fragment);
+ Ok(())
+}
+
+/// Lays out a [`LimitsElem`].
+#[typst_macros::time(name = "math.limits", span = elem.span())]
+pub fn layout_limits(
+ elem: &Packed<LimitsElem>,
+ ctx: &mut MathContext,
+ styles: StyleChain,
+) -> SourceResult<()> {
+ let limits = if elem.inline(styles) { Limits::Always } else { Limits::Display };
+ let mut fragment = ctx.layout_into_fragment(elem.body(), styles)?;
+ fragment.set_limits(limits);
+ ctx.push(fragment);
+ Ok(())
+}
+
+/// Get the size to stretch the base to, if the attach argument is true.
+fn stretch_size(
+ styles: StyleChain,
+ elem: &Packed<AttachElem>,
+) -> Option<Smart<Rel<Length>>> {
+ // Extract from an EquationElem.
+ let mut base = elem.base();
+ if let Some(equation) = base.to_packed::<EquationElem>() {
+ base = equation.body();
+ }
+
+ base.to_packed::<StretchElem>().map(|stretch| stretch.size(styles))
+}
+
+/// Lay out the attachments.
+fn layout_attachments(
+ ctx: &mut MathContext,
+ styles: StyleChain,
+ base: MathFragment,
+ [tl, t, tr, bl, b, br]: [Option<MathFragment>; 6],
+) -> SourceResult<()> {
+ let base_class = base.class();
+
+ // Calculate the distance from the base's baseline to the superscripts' and
+ // subscripts' baseline.
+ let (tx_shift, bx_shift) = if [&tl, &tr, &bl, &br].iter().all(|e| e.is_none()) {
+ (Abs::zero(), Abs::zero())
+ } else {
+ compute_script_shifts(ctx, styles, &base, [&tl, &tr, &bl, &br])
+ };
+
+ // Calculate the distance from the base's baseline to the top attachment's
+ // and bottom attachment's baseline.
+ let (t_shift, b_shift) =
+ compute_limit_shifts(ctx, styles, &base, [t.as_ref(), b.as_ref()]);
+
+ // Calculate the final frame height.
+ let ascent = base
+ .ascent()
+ .max(tx_shift + measure!(tr, ascent))
+ .max(tx_shift + measure!(tl, ascent))
+ .max(t_shift + measure!(t, ascent));
+ let descent = base
+ .descent()
+ .max(bx_shift + measure!(br, descent))
+ .max(bx_shift + measure!(bl, descent))
+ .max(b_shift + measure!(b, descent));
+ let height = ascent + descent;
+
+ // Calculate the vertical position of each element in the final frame.
+ let base_y = ascent - base.ascent();
+ let tx_y = |tx: &MathFragment| ascent - tx_shift - tx.ascent();
+ let bx_y = |bx: &MathFragment| ascent + bx_shift - bx.ascent();
+ let t_y = |t: &MathFragment| ascent - t_shift - t.ascent();
+ let b_y = |b: &MathFragment| ascent + b_shift - b.ascent();
+
+ // Calculate the distance each limit extends to the left and right of the
+ // base's width.
+ let ((t_pre_width, t_post_width), (b_pre_width, b_post_width)) =
+ compute_limit_widths(&base, [t.as_ref(), b.as_ref()]);
+
+ // `space_after_script` is extra spacing that is at the start before each
+ // pre-script, and at the end after each post-script (see the MathConstants
+ // table in the OpenType MATH spec).
+ let space_after_script = scaled!(ctx, styles, space_after_script);
+
+ // Calculate the distance each pre-script extends to the left of the base's
+ // width.
+ let (tl_pre_width, bl_pre_width) = compute_pre_script_widths(
+ ctx,
+ &base,
+ [tl.as_ref(), bl.as_ref()],
+ (tx_shift, bx_shift),
+ space_after_script,
+ );
+
+ // Calculate the distance each post-script extends to the right of the
+ // base's width. Also calculate each post-script's kerning (we need this for
+ // its position later).
+ let ((tr_post_width, tr_kern), (br_post_width, br_kern)) = compute_post_script_widths(
+ ctx,
+ &base,
+ [tr.as_ref(), br.as_ref()],
+ (tx_shift, bx_shift),
+ space_after_script,
+ );
+
+ // Calculate the final frame width.
+ let pre_width = t_pre_width.max(b_pre_width).max(tl_pre_width).max(bl_pre_width);
+ let base_width = base.width();
+ let post_width = t_post_width.max(b_post_width).max(tr_post_width).max(br_post_width);
+ let width = pre_width + base_width + post_width;
+
+ // Calculate the horizontal position of each element in the final frame.
+ let base_x = pre_width;
+ let tl_x = pre_width - tl_pre_width + space_after_script;
+ let bl_x = pre_width - bl_pre_width + space_after_script;
+ let tr_x = pre_width + base_width + tr_kern;
+ let br_x = pre_width + base_width + br_kern;
+ let t_x = pre_width - t_pre_width;
+ let b_x = pre_width - b_pre_width;
+
+ // Create the final frame.
+ let mut frame = Frame::soft(Size::new(width, height));
+ frame.set_baseline(ascent);
+ frame.push_frame(Point::new(base_x, base_y), base.into_frame());
+
+ macro_rules! layout {
+ ($e: ident, $x: ident, $y: ident) => {
+ if let Some($e) = $e {
+ frame.push_frame(Point::new($x, $y(&$e)), $e.into_frame());
+ }
+ };
+ }
+
+ layout!(tl, tl_x, tx_y); // pre-superscript
+ layout!(bl, bl_x, bx_y); // pre-subscript
+ layout!(tr, tr_x, tx_y); // post-superscript
+ layout!(br, br_x, bx_y); // post-subscript
+ layout!(t, t_x, t_y); // upper-limit
+ layout!(b, b_x, b_y); // lower-limit
+
+ // Done! Note that we retain the class of the base.
+ ctx.push(FrameFragment::new(ctx, styles, frame).with_class(base_class));
+
+ Ok(())
+}
+
+/// Calculate the distance each post-script extends to the right of the base's
+/// width, as well as its kerning value. Requires the distance from the base's
+/// baseline to each post-script's baseline to obtain the correct kerning value.
+/// Returns 2 tuples of two lengths, each first containing the distance the
+/// post-script extends left of the base's width and second containing the
+/// post-script's kerning value. The first tuple is for the post-superscript,
+/// and the second is for the post-subscript.
+fn compute_post_script_widths(
+ ctx: &MathContext,
+ base: &MathFragment,
+ [tr, br]: [Option<&MathFragment>; 2],
+ (tr_shift, br_shift): (Abs, Abs),
+ space_after_post_script: Abs,
+) -> ((Abs, Abs), (Abs, Abs)) {
+ let tr_values = tr.map_or_default(|tr| {
+ let kern = math_kern(ctx, base, tr, tr_shift, Corner::TopRight);
+ (space_after_post_script + tr.width() + kern, kern)
+ });
+
+ // The base's bounding box already accounts for its italic correction, so we
+ // need to shift the post-subscript left by the base's italic correction
+ // (see the kerning algorithm as described in the OpenType MATH spec).
+ let br_values = br.map_or_default(|br| {
+ let kern = math_kern(ctx, base, br, br_shift, Corner::BottomRight)
+ - base.italics_correction();
+ (space_after_post_script + br.width() + kern, kern)
+ });
+
+ (tr_values, br_values)
+}
+
+/// Calculate the distance each pre-script extends to the left of the base's
+/// width. Requires the distance from the base's baseline to each pre-script's
+/// baseline to obtain the correct kerning value.
+/// Returns two lengths, the first being the distance the pre-superscript
+/// extends left of the base's width and the second being the distance the
+/// pre-subscript extends left of the base's width.
+fn compute_pre_script_widths(
+ ctx: &MathContext,
+ base: &MathFragment,
+ [tl, bl]: [Option<&MathFragment>; 2],
+ (tl_shift, bl_shift): (Abs, Abs),
+ space_before_pre_script: Abs,
+) -> (Abs, Abs) {
+ let tl_pre_width = tl.map_or_default(|tl| {
+ let kern = math_kern(ctx, base, tl, tl_shift, Corner::TopLeft);
+ space_before_pre_script + tl.width() + kern
+ });
+
+ let bl_pre_width = bl.map_or_default(|bl| {
+ let kern = math_kern(ctx, base, bl, bl_shift, Corner::BottomLeft);
+ space_before_pre_script + bl.width() + kern
+ });
+
+ (tl_pre_width, bl_pre_width)
+}
+
+/// Calculate the distance each limit extends beyond the base's width, in each
+/// direction. Can be a negative value if the limit does not extend beyond the
+/// base's width, indicating how far into the base's width the limit extends.
+/// Returns 2 tuples of two lengths, each first containing the distance the
+/// limit extends leftward beyond the base's width and second containing the
+/// distance the limit extends rightward beyond the base's width. The first
+/// tuple is for the upper-limit, and the second is for the lower-limit.
+fn compute_limit_widths(
+ base: &MathFragment,
+ [t, b]: [Option<&MathFragment>; 2],
+) -> ((Abs, Abs), (Abs, Abs)) {
+ // The upper- (lower-) limit is shifted to the right (left) of the base's
+ // center by half the base's italic correction.
+ let delta = base.italics_correction() / 2.0;
+
+ let t_widths = t.map_or_default(|t| {
+ let half = (t.width() - base.width()) / 2.0;
+ (half - delta, half + delta)
+ });
+
+ let b_widths = b.map_or_default(|b| {
+ let half = (b.width() - base.width()) / 2.0;
+ (half + delta, half - delta)
+ });
+
+ (t_widths, b_widths)
+}
+
+/// Calculate the distance from the base's baseline to each limit's baseline.
+/// Returns two lengths, the first being the distance to the upper-limit's
+/// baseline and the second being the distance to the lower-limit's baseline.
+fn compute_limit_shifts(
+ ctx: &MathContext,
+ styles: StyleChain,
+ base: &MathFragment,
+ [t, b]: [Option<&MathFragment>; 2],
+) -> (Abs, Abs) {
+ // `upper_gap_min` and `lower_gap_min` give gaps to the descender and
+ // ascender of the limits respectively, whereas `upper_rise_min` and
+ // `lower_drop_min` give gaps to each limit's baseline (see the
+ // MathConstants table in the OpenType MATH spec).
+
+ let t_shift = t.map_or_default(|t| {
+ let upper_gap_min = scaled!(ctx, styles, upper_limit_gap_min);
+ let upper_rise_min = scaled!(ctx, styles, upper_limit_baseline_rise_min);
+ base.ascent() + upper_rise_min.max(upper_gap_min + t.descent())
+ });
+
+ let b_shift = b.map_or_default(|b| {
+ let lower_gap_min = scaled!(ctx, styles, lower_limit_gap_min);
+ let lower_drop_min = scaled!(ctx, styles, lower_limit_baseline_drop_min);
+ base.descent() + lower_drop_min.max(lower_gap_min + b.ascent())
+ });
+
+ (t_shift, b_shift)
+}
+
+/// Calculate the distance from the base's baseline to each script's baseline.
+/// Returns two lengths, the first being the distance to the superscripts'
+/// baseline and the second being the distance to the subscripts' baseline.
+fn compute_script_shifts(
+ ctx: &MathContext,
+ styles: StyleChain,
+ base: &MathFragment,
+ [tl, tr, bl, br]: [&Option<MathFragment>; 4],
+) -> (Abs, Abs) {
+ let sup_shift_up = if EquationElem::cramped_in(styles) {
+ scaled!(ctx, styles, superscript_shift_up_cramped)
+ } else {
+ scaled!(ctx, styles, superscript_shift_up)
+ };
+
+ let sup_bottom_min = scaled!(ctx, styles, superscript_bottom_min);
+ let sup_bottom_max_with_sub =
+ scaled!(ctx, styles, superscript_bottom_max_with_subscript);
+ let sup_drop_max = scaled!(ctx, styles, superscript_baseline_drop_max);
+ let gap_min = scaled!(ctx, styles, sub_superscript_gap_min);
+ let sub_shift_down = scaled!(ctx, styles, subscript_shift_down);
+ let sub_top_max = scaled!(ctx, styles, subscript_top_max);
+ let sub_drop_min = scaled!(ctx, styles, subscript_baseline_drop_min);
+
+ let mut shift_up = Abs::zero();
+ let mut shift_down = Abs::zero();
+ let is_text_like = base.is_text_like();
+
+ if tl.is_some() || tr.is_some() {
+ let ascent = match &base {
+ MathFragment::Frame(frame) => frame.base_ascent,
+ _ => base.ascent(),
+ };
+ shift_up = shift_up
+ .max(sup_shift_up)
+ .max(if is_text_like { Abs::zero() } else { ascent - sup_drop_max })
+ .max(sup_bottom_min + measure!(tl, descent))
+ .max(sup_bottom_min + measure!(tr, descent));
+ }
+
+ if bl.is_some() || br.is_some() {
+ shift_down = shift_down
+ .max(sub_shift_down)
+ .max(if is_text_like { Abs::zero() } else { base.descent() + sub_drop_min })
+ .max(measure!(bl, ascent) - sub_top_max)
+ .max(measure!(br, ascent) - sub_top_max);
+ }
+
+ for (sup, sub) in [(tl, bl), (tr, br)] {
+ if let (Some(sup), Some(sub)) = (&sup, &sub) {
+ let sup_bottom = shift_up - sup.descent();
+ let sub_top = sub.ascent() - shift_down;
+ let gap = sup_bottom - sub_top;
+ if gap >= gap_min {
+ continue;
+ }
+
+ let increase = gap_min - gap;
+ let sup_only =
+ (sup_bottom_max_with_sub - sup_bottom).clamp(Abs::zero(), increase);
+ let rest = (increase - sup_only) / 2.0;
+ shift_up += sup_only + rest;
+ shift_down += rest;
+ }
+ }
+
+ (shift_up, shift_down)
+}
+
+/// Calculate the kerning value for a script with respect to the base. A
+/// positive value means shifting the script further away from the base, whereas
+/// a negative value means shifting the script closer to the base. Requires the
+/// distance from the base's baseline to the script's baseline, as well as the
+/// script's corner (tl, tr, bl, br).
+fn math_kern(
+ ctx: &MathContext,
+ base: &MathFragment,
+ script: &MathFragment,
+ shift: Abs,
+ pos: Corner,
+) -> Abs {
+ // This process is described under the MathKernInfo table in the OpenType
+ // MATH spec.
+
+ let (corr_height_top, corr_height_bot) = match pos {
+ // Calculate two correction heights for superscripts:
+ // - The distance from the superscript's baseline to the top of the
+ // base's bounding box.
+ // - The distance from the base's baseline to the bottom of the
+ // superscript's bounding box.
+ Corner::TopLeft | Corner::TopRight => {
+ (base.ascent() - shift, shift - script.descent())
+ }
+ // Calculate two correction heights for subscripts:
+ // - The distance from the base's baseline to the top of the
+ // subscript's bounding box.
+ // - The distance from the subscript's baseline to the bottom of the
+ // base's bounding box.
+ Corner::BottomLeft | Corner::BottomRight => {
+ (script.ascent() - shift, shift - base.descent())
+ }
+ };
+
+ // Calculate the sum of kerning values for each correction height.
+ let summed_kern = |height| {
+ let base_kern = base.kern_at_height(ctx, pos, height);
+ let attach_kern = script.kern_at_height(ctx, pos.inv(), height);
+ base_kern + attach_kern
+ };
+
+ // Take the smaller kerning amount (and so the larger value). Note that
+ // there is a bug in the spec (as of 2024-08-15): it says to take the
+ // minimum of the two sums, but as the kerning value is usually negative it
+ // really means the smaller kern. The current wording of the spec could
+ // result in glyphs colliding.
+ summed_kern(corr_height_top).max(summed_kern(corr_height_bot))
+}
generated by cgit v1.2.3 (git 2.25.1) at 2026-03-15 14:18:18 +0000