More robust automatic math spacing

library/src/math/accent.rs

@@ -118,7 +118,7 @@ impl LayoutMath for AccentNode {
         frame.set_baseline(baseline);
         frame.push_frame(accent_pos, accent);
         frame.push_frame(base_pos, base.to_frame(ctx));
-        ctx.push(frame);
+        ctx.push(FrameFragment::new(ctx, frame));
 
         Ok(())
     }

library/src/math/align.rs

@@ -29,8 +29,7 @@ pub(super) fn alignments(rows: &[MathRow]) -> Vec<Abs> {
     let count = rows
         .iter()
         .map(|row| {
-            row.0
-                .iter()
+            row.iter()
                 .filter(|fragment| matches!(fragment, MathFragment::Align))
                 .count()
         })
@@ -42,7 +41,7 @@ pub(super) fn alignments(rows: &[MathRow]) -> Vec<Abs> {
         for row in rows {
             let mut x = Abs::zero();
             let mut i = 0;
-            for fragment in &row.0 {
+            for fragment in row.iter() {
                 if matches!(fragment, MathFragment::Align) {
                     if i < current {
                         x = points[i];

library/src/math/attach.rs

@@ -231,7 +231,7 @@ fn scripts(
         frame.push_frame(sub_pos, sub);
     }
 
-    ctx.push(FrameFragment::new(frame).with_class(class));
+    ctx.push(FrameFragment::new(ctx, frame).with_class(class));
 
     Ok(())
 }
@@ -284,7 +284,7 @@ fn limits(
         frame.push_frame(bottom_pos, bottom);
     }
 
-    ctx.push(FrameFragment::new(frame).with_class(class));
+    ctx.push(FrameFragment::new(ctx, frame).with_class(class));
 
     Ok(())
 }

library/src/math/ctx.rs

@@ -31,7 +31,7 @@ pub struct MathContext<'a, 'b, 'v> {
     pub table: ttf_parser::math::Table<'a>,
     pub constants: ttf_parser::math::Constants<'a>,
     pub space_width: Em,
-    pub row: MathRow,
+    pub fragments: Vec<MathFragment>,
     pub map: StyleMap,
     pub style: MathStyle,
     pub size: Abs,
@@ -69,7 +69,7 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
             table,
             constants,
             space_width,
-            row: MathRow::new(),
+            fragments: vec![],
             map: StyleMap::new(),
             style: MathStyle {
                 variant: MathVariant::Serif,
@@ -88,45 +88,45 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
     }
 
     pub fn push(&mut self, fragment: impl Into<MathFragment>) {
-        self.row.push(self.size, self.space_width, self.style, fragment);
+        self.fragments.push(fragment.into());
     }
 
-    pub fn extend(&mut self, row: MathRow) {
-        let mut iter = row.0.into_iter();
-        if let Some(first) = iter.next() {
-            self.push(first);
-        }
-        self.row.0.extend(iter);
-    }
-
-    pub fn layout_non_math(&mut self, content: &Content) -> SourceResult<Frame> {
-        Ok(content
-            .layout(&mut self.vt, self.outer.chain(&self.map), self.regions)?
-            .into_frame())
+    pub fn extend(&mut self, fragments: Vec<MathFragment>) {
+        self.fragments.extend(fragments);
     }
 
     pub fn layout_fragment(
         &mut self,
         node: &dyn LayoutMath,
     ) -> SourceResult<MathFragment> {
-        let row = self.layout_row(node)?;
-        Ok(if row.0.len() == 1 {
-            row.0.into_iter().next().unwrap()
-        } else {
-            row.to_frame(self).into()
-        })
+        let row = self.layout_fragments(node)?;
+        Ok(MathRow::new(row).to_fragment(self))
+    }
+
+    pub fn layout_fragments(
+        &mut self,
+        node: &dyn LayoutMath,
+    ) -> SourceResult<Vec<MathFragment>> {
+        let prev = std::mem::take(&mut self.fragments);
+        node.layout_math(self)?;
+        Ok(std::mem::replace(&mut self.fragments, prev))
     }
 
     pub fn layout_row(&mut self, node: &dyn LayoutMath) -> SourceResult<MathRow> {
-        let prev = std::mem::take(&mut self.row);
-        node.layout_math(self)?;
-        Ok(std::mem::replace(&mut self.row, prev))
+        let fragments = self.layout_fragments(node)?;
+        Ok(MathRow::new(fragments))
     }
 
     pub fn layout_frame(&mut self, node: &dyn LayoutMath) -> SourceResult<Frame> {
         Ok(self.layout_fragment(node)?.to_frame(self))
     }
 
+    pub fn layout_content(&mut self, content: &Content) -> SourceResult<Frame> {
+        Ok(content
+            .layout(&mut self.vt, self.outer.chain(&self.map), self.regions)?
+            .into_frame())
+    }
+
     pub fn layout_text(&mut self, text: &str) -> SourceResult<()> {
         let mut chars = text.chars();
         if let Some(glyph) = chars
@@ -146,13 +146,13 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
             }
         } else if text.chars().all(|c| c.is_ascii_digit()) {
             // Numbers aren't that difficult.
-            let mut vec = vec![];
+            let mut fragments = vec![];
             for c in text.chars() {
                 let c = self.style.styled_char(c);
-                vec.push(GlyphFragment::new(self, c).into());
+                fragments.push(GlyphFragment::new(self, c).into());
             }
-            let frame = MathRow(vec).to_frame(self);
-            self.push(frame);
+            let frame = MathRow::new(fragments).to_frame(self);
+            self.push(FrameFragment::new(self, frame));
         } else {
             // Anything else is handled by Typst's standard text layout.
             let spaced = text.graphemes(true).count() > 1;
@@ -161,9 +161,9 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
                 style = style.with_italic(false);
             }
             let text: EcoString = text.chars().map(|c| style.styled_char(c)).collect();
-            let frame = self.layout_non_math(&TextNode::packed(text))?;
+            let frame = self.layout_content(&TextNode::packed(text))?;
             self.push(
-                FrameFragment::new(frame)
+                FrameFragment::new(self, frame)
                     .with_class(MathClass::Alphabetic)
                     .with_spaced(spaced),
             );

library/src/math/delimited.rs

@@ -60,10 +60,9 @@ impl LayoutMath for LrNode {
             }
         }
 
-        let mut row = ctx.layout_row(body)?;
+        let mut fragments = ctx.layout_fragments(body)?;
         let axis = scaled!(ctx, axis_height);
-        let max_extent = row
-            .0
+        let max_extent = fragments
             .iter()
             .map(|fragment| (fragment.ascent() - axis).max(fragment.descent() + axis))
             .max()
@@ -75,7 +74,7 @@ impl LayoutMath for LrNode {
             .resolve(ctx.styles())
             .relative_to(2.0 * max_extent);
 
-        match row.0.as_mut_slice() {
+        match fragments.as_mut_slice() {
             [one] => scale(ctx, one, height, None),
             [first, .., last] => {
                 scale(ctx, first, height, Some(MathClass::Opening));
@@ -84,7 +83,7 @@ impl LayoutMath for LrNode {
             _ => {}
         }
 
-        ctx.extend(row);
+        ctx.extend(fragments);
 
         Ok(())
     }

library/src/math/frac.rs

@@ -153,7 +153,7 @@ fn layout(
 
     if binom {
         ctx.push(GlyphFragment::new(ctx, '(').stretch_vertical(ctx, height, short_fall));
-        ctx.push(frame);
+        ctx.push(FrameFragment::new(ctx, frame));
         ctx.push(GlyphFragment::new(ctx, ')').stretch_vertical(ctx, height, short_fall));
     } else {
         frame.push(
@@ -165,7 +165,7 @@ fn layout(
                 }),
             ),
         );
-        ctx.push(frame);
+        ctx.push(FrameFragment::new(ctx, frame));
     }
 
     Ok(())

library/src/math/fragment.rs

@@ -6,7 +6,7 @@ pub enum MathFragment {
     Variant(VariantFragment),
     Frame(FrameFragment),
     Spacing(Abs),
-    Space,
+    Space(Abs),
     Linebreak,
     Align,
 }
@@ -22,6 +22,7 @@ impl MathFragment {
             Self::Variant(variant) => variant.frame.width(),
             Self::Frame(fragment) => fragment.frame.width(),
             Self::Spacing(amount) => *amount,
+            Self::Space(amount) => *amount,
             _ => Abs::zero(),
         }
     }
@@ -62,6 +63,24 @@ impl MathFragment {
         }
     }
 
+    pub fn style(&self) -> Option<MathStyle> {
+        match self {
+            Self::Glyph(glyph) => Some(glyph.style),
+            Self::Variant(variant) => Some(variant.style),
+            Self::Frame(fragment) => Some(fragment.style),
+            _ => None,
+        }
+    }
+
+    pub fn font_size(&self) -> Option<Abs> {
+        match self {
+            Self::Glyph(glyph) => Some(glyph.font_size),
+            Self::Variant(variant) => Some(variant.font_size),
+            Self::Frame(fragment) => Some(fragment.font_size),
+            _ => None,
+        }
+    }
+
     pub fn set_class(&mut self, class: MathClass) {
         match self {
             Self::Glyph(glyph) => glyph.class = Some(class),
@@ -71,8 +90,11 @@ impl MathFragment {
         }
     }
 
-    pub fn participating(&self) -> bool {
-        !matches!(self, Self::Space | Self::Spacing(_) | Self::Align)
+    pub fn is_spaced(&self) -> bool {
+        match self {
+            MathFragment::Frame(frame) => frame.spaced,
+            _ => self.class() == Some(MathClass::Fence),
+        }
     }
 
     pub fn italics_correction(&self) -> Abs {
@@ -111,23 +133,18 @@ impl From<FrameFragment> for MathFragment {
     }
 }
 
-impl From<Frame> for MathFragment {
-    fn from(frame: Frame) -> Self {
-        Self::Frame(FrameFragment::new(frame))
-    }
-}
-
-#[derive(Debug, Clone, Copy)]
+#[derive(Clone, Copy)]
 pub struct GlyphFragment {
     pub id: GlyphId,
     pub c: char,
     pub lang: Lang,
     pub fill: Paint,
-    pub font_size: Abs,
     pub width: Abs,
     pub ascent: Abs,
     pub descent: Abs,
     pub italics_correction: Abs,
+    pub style: MathStyle,
+    pub font_size: Abs,
     pub class: Option<MathClass>,
 }
 
@@ -163,6 +180,7 @@ impl GlyphFragment {
             c,
             lang: ctx.styles().get(TextNode::LANG),
             fill: ctx.styles().get(TextNode::FILL),
+            style: ctx.style,
             font_size: ctx.size,
             width,
             ascent: bbox.y_max.scaled(ctx),
@@ -184,6 +202,8 @@ impl GlyphFragment {
             c: self.c,
             id: Some(self.id),
             frame: self.to_frame(ctx),
+            style: self.style,
+            font_size: self.font_size,
             italics_correction: self.italics_correction,
             class: self.class,
         }
@@ -210,30 +230,48 @@ impl GlyphFragment {
     }
 }
 
-#[derive(Debug, Clone)]
+impl Debug for GlyphFragment {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "GlyphFragment({:?})", self.c)
+    }
+}
+
+#[derive(Clone)]
 pub struct VariantFragment {
     pub c: char,
     pub id: Option<GlyphId>,
-    pub frame: Frame,
     pub italics_correction: Abs,
+    pub frame: Frame,
+    pub style: MathStyle,
+    pub font_size: Abs,
     pub class: Option<MathClass>,
 }
 
+impl Debug for VariantFragment {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "VariantFragment({:?})", self.c)
+    }
+}
+
 #[derive(Debug, Clone)]
 pub struct FrameFragment {
     pub frame: Frame,
-    pub class: MathClass,
     pub limits: bool,
     pub spaced: bool,
+    pub style: MathStyle,
+    pub font_size: Abs,
+    pub class: MathClass,
 }
 
 impl FrameFragment {
-    pub fn new(frame: Frame) -> Self {
+    pub fn new(ctx: &MathContext, frame: Frame) -> Self {
         Self {
             frame,
-            class: MathClass::Normal,
             limits: false,
             spaced: false,
+            font_size: ctx.size,
+            style: ctx.style,
+            class: MathClass::Normal,
         }
     }
 

library/src/math/matrix.rs

@@ -307,7 +307,7 @@ fn layout_delimiters(
         ctx.push(GlyphFragment::new(ctx, left).stretch_vertical(ctx, target, short_fall));
     }
 
-    ctx.push(frame);
+    ctx.push(FrameFragment::new(ctx, frame));
 
     if let Some(right) = right {
         ctx.push(

library/src/math/mod.rs

@@ -261,7 +261,7 @@ impl LayoutMath for Content {
         }
 
         if self.is::<SpaceNode>() {
-            ctx.push(MathFragment::Space);
+            ctx.push(MathFragment::Space(ctx.space_width.scaled(ctx)));
             return Ok(());
         }
 
@@ -288,8 +288,8 @@ impl LayoutMath for Content {
             return node.layout_math(ctx);
         }
 
-        let frame = ctx.layout_non_math(self)?;
-        ctx.push(FrameFragment::new(frame).with_spaced(true));
+        let frame = ctx.layout_content(self)?;
+        ctx.push(FrameFragment::new(ctx, frame).with_spaced(true));
 
         Ok(())
     }

library/src/math/op.rs

@@ -38,9 +38,9 @@ impl OpNode {
 
 impl LayoutMath for OpNode {
     fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
-        let frame = ctx.layout_non_math(&TextNode(self.text.clone()).pack())?;
+        let frame = ctx.layout_content(&TextNode(self.text.clone()).pack())?;
         ctx.push(
-            FrameFragment::new(frame)
+            FrameFragment::new(ctx, frame)
                 .with_class(MathClass::Large)
                 .with_limits(self.limits),
         );

library/src/math/root.rs

@@ -158,7 +158,7 @@ fn layout(
     );
 
     frame.push_frame(radicand_pos, radicand);
-    ctx.push(frame);
+    ctx.push(FrameFragment::new(ctx, frame));
 
     Ok(())
 }

library/src/math/row.rs

@@ -5,55 +5,55 @@ use super::*;
 pub const TIGHT_LEADING: Em = Em::new(0.25);
 
 #[derive(Debug, Default, Clone)]
-pub struct MathRow(pub Vec<MathFragment>);
+pub struct MathRow(Vec<MathFragment>);
 
 impl MathRow {
-    pub fn new() -> Self {
-        Self(vec![])
-    }
+    pub fn new(fragments: Vec<MathFragment>) -> Self {
+        let mut iter = fragments.into_iter().peekable();
+        let mut last: Option<usize> = None;
+        let mut space: Option<MathFragment> = None;
+        let mut resolved: Vec<MathFragment> = vec![];
 
-    pub fn width(&self) -> Abs {
-        self.0.iter().map(|fragment| fragment.width()).sum()
-    }
-
-    pub fn height(&self) -> Abs {
-        self.ascent() + self.descent()
-    }
-
-    pub fn ascent(&self) -> Abs {
-        self.0.iter().map(MathFragment::ascent).max().unwrap_or_default()
-    }
-
-    pub fn descent(&self) -> Abs {
-        self.0.iter().map(MathFragment::descent).max().unwrap_or_default()
-    }
-
-    pub fn push(
-        &mut self,
-        font_size: Abs,
-        space_width: Em,
-        style: MathStyle,
-        fragment: impl Into<MathFragment>,
-    ) {
-        let mut fragment = fragment.into();
-        if !fragment.participating() {
-            self.0.push(fragment);
-            return;
-        }
-
-        let mut space = false;
-        for (i, prev) in self.0.iter().enumerate().rev() {
-            if !prev.participating() {
-                space |= matches!(prev, MathFragment::Space);
-                if matches!(prev, MathFragment::Spacing(_)) {
-                    break;
+        while let Some(mut fragment) = iter.next() {
+            match fragment {
+                // Keep space only if supported by spaced fragments.
+                MathFragment::Space(_) => {
+                    if last.is_some() {
+                        space = Some(fragment);
                     }
                     continue;
                 }
 
-            if fragment.class() == Some(MathClass::Vary) {
-                if matches!(
-                    prev.class(),
+                // Explicit spacing disables automatic spacing.
+                MathFragment::Spacing(_) => {
+                    last = None;
+                    space = None;
+                    resolved.push(fragment);
+                    continue;
+                }
+
+                // Alignment points are resolved later.
+                MathFragment::Align => {
+                    resolved.push(fragment);
+                    continue;
+                }
+
+                // New line, new things.
+                MathFragment::Linebreak => {
+                    resolved.push(fragment);
+                    space = None;
+                    last = None;
+                    continue;
+                }
+
+                _ => {}
+            }
+
+            // Convert variable operators into binary operators if something
+            // precedes them.
+            if fragment.class() == Some(MathClass::Vary)
+                && matches!(
+                    last.and_then(|i| resolved[i].class()),
                     Some(
                         MathClass::Normal
                             | MathClass::Alphabetic
@@ -62,22 +62,43 @@ impl MathRow {
                             | MathClass::Fence
                             | MathClass::Relation
                     )
-                ) {
+                )
+            {
                 fragment.set_class(MathClass::Binary);
             }
+
+            // Insert spacing between the last and this item.
+            if let Some(i) = last {
+                if let Some(s) = spacing(&resolved[i], space.take(), &fragment) {
+                    resolved.insert(i + 1, s);
+                }
             }
 
-            let mut amount = Abs::zero();
-            amount += spacing(prev, &fragment, style, space, space_width).at(font_size);
-
-            if !amount.is_zero() {
-                self.0.insert(i + 1, MathFragment::Spacing(amount));
+            last = Some(resolved.len());
+            resolved.push(fragment);
         }
 
-            break;
+        Self(resolved)
     }
 
-        self.0.push(fragment);
+    pub fn iter(&self) -> std::slice::Iter<'_, MathFragment> {
+        self.0.iter()
+    }
+
+    pub fn width(&self) -> Abs {
+        self.iter().map(MathFragment::width).sum()
+    }
+
+    pub fn height(&self) -> Abs {
+        self.ascent() + self.descent()
+    }
+
+    pub fn ascent(&self) -> Abs {
+        self.iter().map(MathFragment::ascent).max().unwrap_or_default()
+    }
+
+    pub fn descent(&self) -> Abs {
+        self.iter().map(MathFragment::descent).max().unwrap_or_default()
     }
 
     pub fn to_frame(self, ctx: &MathContext) -> Frame {
@@ -86,14 +107,22 @@ impl MathRow {
         self.to_aligned_frame(ctx, &[], align)
     }
 
+    pub fn to_fragment(self, ctx: &MathContext) -> MathFragment {
+        if self.0.len() == 1 {
+            self.0.into_iter().next().unwrap()
+        } else {
+            FrameFragment::new(ctx, self.to_frame(ctx)).into()
+        }
+    }
+
     pub fn to_aligned_frame(
         mut self,
         ctx: &MathContext,
         points: &[Abs],
         align: Align,
     ) -> Frame {
-        if self.0.iter().any(|frag| matches!(frag, MathFragment::Linebreak)) {
-            let fragments = std::mem::take(&mut self.0);
+        if self.iter().any(|frag| matches!(frag, MathFragment::Linebreak)) {
+            let fragments: Vec<_> = std::mem::take(&mut self.0);
             let leading = if ctx.style.size >= MathSize::Text {
                 ctx.styles().get(ParNode::LEADING)
             } else {
@@ -140,7 +169,7 @@ impl MathRow {
 
         if let (Some(&first), Align::Center) = (points.first(), align) {
             let mut offset = first;
-            for fragment in &self.0 {
+            for fragment in self.iter() {
                 offset -= fragment.width();
                 if matches!(fragment, MathFragment::Align) {
                     x = offset;

library/src/math/spacing.rs

@@ -1,6 +1,5 @@
 use super::*;
 
-pub(super) const ZERO: Em = Em::zero();
 pub(super) const THIN: Em = Em::new(1.0 / 6.0);
 pub(super) const MEDIUM: Em = Em::new(2.0 / 9.0);
 pub(super) const THICK: Em = Em::new(5.0 / 18.0);
@@ -14,49 +13,48 @@ pub(super) fn define(math: &mut Scope) {
     math.define("quad", HNode::strong(QUAD).pack());
 }
 
-/// Determine the spacing between two fragments in a given style.
+/// Create the spacing between two fragments in a given style.
 pub(super) fn spacing(
-    left: &MathFragment,
-    right: &MathFragment,
-    style: MathStyle,
-    space: bool,
-    space_width: Em,
-) -> Em {
+    l: &MathFragment,
+    space: Option<MathFragment>,
+    r: &MathFragment,
+) -> Option<MathFragment> {
     use MathClass::*;
-    let script = style.size <= MathSize::Script;
-    let class = |frag: &MathFragment| frag.class().unwrap_or(Special);
-    match (class(left), class(right)) {
+
+    let class = |f: &MathFragment| f.class().unwrap_or(Special);
+    let resolve = |v: Em, f: &MathFragment| {
+        Some(MathFragment::Spacing(f.font_size().map_or(Abs::zero(), |size| v.at(size))))
+    };
+    let script =
+        |f: &MathFragment| f.style().map_or(false, |s| s.size <= MathSize::Script);
+
+    match (class(l), class(r)) {
         // No spacing before punctuation; thin spacing after punctuation, unless
         // in script size.
-        (_, Punctuation) => ZERO,
-        (Punctuation, _) if !script => THIN,
+        (_, Punctuation) => None,
+        (Punctuation, _) if !script(l) => resolve(THIN, l),
 
         // No spacing after opening delimiters and before closing delimiters.
-        (Opening, _) | (_, Closing) => ZERO,
+        (Opening, _) | (_, Closing) => None,
 
         // Thick spacing around relations, unless followed by a another relation
         // or in script size.
-        (Relation, Relation) => ZERO,
-        (Relation, _) | (_, Relation) if !script => THICK,
+        (Relation, Relation) => None,
+        (Relation, _) if !script(l) => resolve(THICK, l),
+        (_, Relation) if !script(r) => resolve(THICK, r),
 
         // Medium spacing around binary operators, unless in script size.
-        (Binary, _) | (_, Binary) if !script => MEDIUM,
+        (Binary, _) if !script(l) => resolve(MEDIUM, l),
+        (_, Binary) if !script(r) => resolve(MEDIUM, r),
 
         // Thin spacing around large operators, unless next to a delimiter.
-        (Large, Opening | Fence) | (Closing | Fence, Large) => ZERO,
-        (Large, _) | (_, Large) => THIN,
+        (Large, Opening | Fence) | (Closing | Fence, Large) => None,
+        (Large, _) => resolve(THIN, l),
+        (_, Large) => resolve(THIN, r),
 
         // Spacing around spaced frames.
-        _ if space && (is_spaced(left) || is_spaced(right)) => space_width,
+        _ if (l.is_spaced() || r.is_spaced()) => space,
 
-        _ => ZERO,
-    }
-}
-
-/// Whether this fragment should react to adjacent spaces.
-fn is_spaced(fragment: &MathFragment) -> bool {
-    match fragment {
-        MathFragment::Frame(frame) => frame.spaced,
-        _ => fragment.class() == Some(MathClass::Fence),
+        _ => None,
     }
 }

library/src/math/stretch.rs

@@ -177,6 +177,8 @@ fn assemble(
         c: base.c,
         id: None,
         frame,
+        style: base.style,
+        font_size: base.font_size,
         italics_correction: Abs::zero(),
         class: base.class,
     }

library/src/math/style.rs

@@ -313,7 +313,7 @@ impl LayoutMath for BbNode {
     }
 }
 
-/// The style in a formula.
+/// Text properties in a formula.
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub struct MathStyle {
     /// The style variant to select.

library/src/math/underover.rs

@@ -270,7 +270,8 @@ fn layout(
         baseline = rows.len() - 1;
     }
 
-    ctx.push(stack(ctx, rows, Align::Center, gap, baseline));
+    let frame = stack(ctx, rows, Align::Center, gap, baseline);
+    ctx.push(FrameFragment::new(ctx, frame));
 
     Ok(())
 }