Sub- and superscripts

Fixes to PDF export I guess
Also improved rendition for non-Latin scripts

5 files changed, 213 insertions, 12 deletions

diff --git a/src/library/mod.rs b/src/library/mod.rs
index 9708475b..d78e38ca 100644
--- a/src/library/mod.rs
+++ b/src/library/mod.rs
@@ -28,6 +28,8 @@ pub fn new() -> Scope {
     std.def_node::<text::UnderlineNode>("underline");
     std.def_node::<text::StrikethroughNode>("strike");
     std.def_node::<text::OverlineNode>("overline");
+    std.def_node::<text::SuperNode>("super");
+    std.def_node::<text::SubNode>("sub");
     std.def_node::<text::LinkNode>("link");
     std.def_node::<text::RepeatNode>("repeat");
     std.def_fn("lower", text::lower);
diff --git a/src/library/text/mod.rs b/src/library/text/mod.rs
index a1089486..be20b3ef 100644
--- a/src/library/text/mod.rs
+++ b/src/library/text/mod.rs
@@ -8,6 +8,7 @@ mod quotes;
 mod raw;
 mod repeat;
 mod shaping;
+mod shift;
 
 pub use deco::*;
 pub use lang::*;
@@ -17,6 +18,7 @@ pub use quotes::*;
 pub use raw::*;
 pub use repeat::*;
 pub use shaping::*;
+pub use shift::*;
 
 use std::borrow::Cow;
 
@@ -60,6 +62,9 @@ impl TextNode {
     /// The width of spaces relative to the default space width.
     #[property(resolve)]
     pub const SPACING: Relative<RawLength> = Relative::one();
+    /// The offset of the baseline.
+    #[property(resolve)]
+    pub const BASELINE: RawLength = RawLength::zero();
     /// Whether glyphs can hang over into the margin.
     pub const OVERHANG: bool = true;
     /// The top end of the text bounding box.
@@ -98,8 +103,6 @@ impl TextNode {
     pub const NUMBER_TYPE: Smart<NumberType> = Smart::Auto;
     /// The width of numbers / figures.
     pub const NUMBER_WIDTH: Smart<NumberWidth> = Smart::Auto;
-    /// How to position numbers.
-    pub const NUMBER_POSITION: NumberPosition = NumberPosition::Normal;
     /// Whether to have a slash through the zero glyph. ("zero")
     pub const SLASHED_ZERO: bool = false;
     /// Whether to convert fractions. ("frac")
diff --git a/src/library/text/par.rs b/src/library/text/par.rs
index a6f7c273..d86eb175 100644
--- a/src/library/text/par.rs
+++ b/src/library/text/par.rs
@@ -551,7 +551,16 @@ fn prepare<'a>(
                 } else {
                     let size = Size::new(regions.first.x, regions.base.y);
                     let pod = Regions::one(size, regions.base, Spec::splat(false));
-                    let frame = node.layout(ctx, &pod, styles)?.remove(0);
+                    let mut frame = node.layout(ctx, &pod, styles)?.remove(0);
+                    let shift = styles.get(TextNode::BASELINE);
+
+                    if !shift.is_zero() {
+                        Arc::make_mut(&mut frame).baseline = Some(
+                            frame.baseline.unwrap_or(frame.size.y)
+                                - styles.get(TextNode::BASELINE),
+                        );
+                    }
+
                     items.push(Item::Frame(frame));
                 }
             }
diff --git a/src/library/text/shaping.rs b/src/library/text/shaping.rs
index 68499a01..67fabbd5 100644
--- a/src/library/text/shaping.rs
+++ b/src/library/text/shaping.rs
@@ -41,6 +41,8 @@ pub struct ShapedGlyph {
     pub x_advance: Em,
     /// The horizontal offset of the glyph.
     pub x_offset: Em,
+    /// The vertical offset of the glyph.
+    pub y_offset: Em,
     /// A value that is the same for all glyphs belong to one cluster.
     pub cluster: usize,
     /// Whether splitting the shaping result before this glyph would yield the
@@ -84,8 +86,10 @@ impl<'a> ShapedText<'a> {
         let mut frame = Frame::new(size);
         frame.baseline = Some(top);
 
-        for (face_id, group) in self.glyphs.as_ref().group_by_key(|g| g.face_id) {
-            let pos = Point::new(offset, top);
+        for ((face_id, y_offset), group) in
+            self.glyphs.as_ref().group_by_key(|g| (g.face_id, g.y_offset))
+        {
+            let pos = Point::new(offset, top + y_offset.at(self.size));
 
             let fill = self.styles.get(TextNode::FILL);
             let glyphs = group
@@ -212,11 +216,14 @@ impl<'a> ShapedText<'a> {
             let x_advance = face.to_em(ttf.glyph_hor_advance(glyph_id)?);
             let cluster = self.glyphs.last().map(|g| g.cluster).unwrap_or_default();
             self.width += x_advance.at(self.size);
+            let baseline_shift = self.styles.get(TextNode::BASELINE);
+
             self.glyphs.to_mut().push(ShapedGlyph {
                 face_id,
                 glyph_id: glyph_id.0,
                 x_advance,
                 x_offset: Em::zero(),
+                y_offset: Em::from_length(baseline_shift, self.size),
                 cluster,
                 safe_to_break: true,
                 c: '-',
@@ -401,13 +408,17 @@ fn shape_segment<'a>(
         let cluster = info.cluster as usize;
 
         if info.glyph_id != 0 {
+            let baseline_shift = ctx.styles.get(TextNode::BASELINE);
+
             // Add the glyph to the shaped output.
-            // TODO: Don't ignore y_advance and y_offset.
+            // TODO: Don't ignore y_advance.
             ctx.glyphs.push(ShapedGlyph {
                 face_id,
                 glyph_id: info.glyph_id as u16,
                 x_advance: face.to_em(pos[i].x_advance),
                 x_offset: face.to_em(pos[i].x_offset),
+                y_offset: face.to_em(pos[i].y_offset)
+                    + Em::from_length(baseline_shift, ctx.size),
                 cluster: base + cluster,
                 safe_to_break: !info.unsafe_to_break(),
                 c: text[cluster ..].chars().next().unwrap(),
@@ -478,6 +489,7 @@ fn shape_tofus(ctx: &mut ShapingContext, base: usize, text: &str, face_id: FaceI
             glyph_id: 0,
             x_advance,
             x_offset: Em::zero(),
+            y_offset: Em::from_length(ctx.styles.get(TextNode::BASELINE), ctx.size),
             cluster: base + cluster,
             safe_to_break: true,
             c,
@@ -602,12 +614,6 @@ fn tags(styles: StyleChain) -> Vec<Feature> {
         Smart::Custom(NumberWidth::Tabular) => feat(b"tnum", 1),
     }
 
-    match styles.get(TextNode::NUMBER_POSITION) {
-        NumberPosition::Normal => {}
-        NumberPosition::Subscript => feat(b"subs", 1),
-        NumberPosition::Superscript => feat(b"sups", 1),
-    }
-
     if styles.get(TextNode::SLASHED_ZERO) {
         feat(b"zero", 1);
     }
diff --git a/src/library/text/shift.rs b/src/library/text/shift.rs
new file mode 100644
index 00000000..3efa3720
--- /dev/null
+++ b/src/library/text/shift.rs
@@ -0,0 +1,181 @@
+use super::{variant, TextNode, TextSize};
+use crate::font::FontStore;
+use crate::library::prelude::*;
+use crate::util::EcoString;
+
+/// Sub or superscript text. The text is rendered smaller and its baseline is raised.
+///
+/// To provide the best typography possible, we first try to transform the
+/// text to superscript codepoints. If that fails, we fall back to rendering
+/// shrunk normal letters in a raised way.
+#[derive(Debug, Hash)]
+pub struct ShiftNode<const S: ScriptKind>(pub Content);
+
+/// Shift the text into superscript.
+pub type SuperNode = ShiftNode<SUPERSCRIPT>;
+
+/// Shift the text into subscript.
+pub type SubNode = ShiftNode<SUBSCRIPT>;
+
+#[node(showable)]
+impl<const S: ScriptKind> ShiftNode<S> {
+    /// Whether to prefer the dedicated sub- and superscript characters of the font.
+    pub const TYPOGRAPHIC: bool = true;
+    /// The baseline shift for synthetic sub- and superscripts.
+    pub const BASELINE: RawLength =
+        Em::new(if S == SUPERSCRIPT { -0.5 } else { 0.2 }).into();
+    /// The font size for synthetic sub- and superscripts.
+    pub const SIZE: TextSize = TextSize(Em::new(0.6).into());
+
+    fn construct(_: &mut Machine, args: &mut Args) -> TypResult<Content> {
+        Ok(Content::show(Self(args.expect("body")?)))
+    }
+}
+
+impl<const S: ScriptKind> Show for ShiftNode<S> {
+    fn unguard(&self, sel: Selector) -> ShowNode {
+        Self(self.0.unguard(sel)).pack()
+    }
+
+    fn encode(&self, _: StyleChain) -> Dict {
+        dict! { "body" => Value::Content(self.0.clone()) }
+    }
+
+    fn realize(&self, ctx: &mut Context, styles: StyleChain) -> TypResult<Content> {
+        let mut transformed = None;
+        if styles.get(ShiftNode::<S>::TYPOGRAPHIC) {
+            if let Some(text) = search_text(&self.0, S) {
+                if check_str_in_family(&mut ctx.fonts, &text, styles) {
+                    transformed = Some(Content::Text(text));
+                }
+            }
+        };
+
+        Ok(transformed.unwrap_or_else(|| {
+            let mut map = StyleMap::new();
+            map.set(TextNode::BASELINE, styles.get(ShiftNode::<S>::BASELINE));
+            map.set(TextNode::SIZE, styles.get(ShiftNode::<S>::SIZE));
+            self.0.clone().styled_with_map(map)
+        }))
+    }
+}
+
+/// Find and transform the text contained in `content` iff it only consists of
+/// `Text`, `Space`, and `Empty` leaf nodes. The text is transformed to the
+/// given script kind.
+fn search_text(content: &Content, mode: ScriptKind) -> Option<EcoString> {
+    match content {
+        Content::Text(_) => {
+            if let Content::Text(t) = content {
+                if let Some(sup) = convert_script(t, mode) {
+                    return Some(sup);
+                }
+            }
+            None
+        }
+        Content::Space => Some(EcoString::from(" ")),
+        Content::Empty => Some(EcoString::new()),
+        Content::Styled(arc) => search_text(&arc.0, mode),
+        Content::Sequence(seq) => {
+            let mut full = EcoString::new();
+            for item in seq.iter() {
+                match search_text(item, mode) {
+                    Some(text) => full.push_str(&text),
+                    None => return None,
+                }
+            }
+            Some(full)
+        }
+        _ => None,
+    }
+}
+
+/// Checks whether the first retrievable family contains all code points of the
+/// given string.
+fn check_str_in_family(fonts: &mut FontStore, text: &str, styles: StyleChain) -> bool {
+    for family in styles.get(TextNode::FAMILY).iter() {
+        if let Some(face_id) = fonts.select(family.as_str(), variant(styles)) {
+            let face = fonts.get(face_id);
+            let ttf = face.ttf();
+            return text.chars().all(|c| ttf.glyph_index(c).is_some());
+        }
+    }
+
+    false
+}
+
+/// Convert a string to sub- or superscript codepoints if all characters
+/// can be mapped to such a codepoint.
+fn convert_script(text: &str, mode: ScriptKind) -> Option<EcoString> {
+    let mut result = EcoString::with_capacity(text.len());
+    let converter = match mode {
+        SUPERSCRIPT => to_superscript_codepoint,
+        SUBSCRIPT => to_subscript_codepoint,
+        _ => panic!("unknown script kind"),
+    };
+
+    for c in text.chars() {
+        match converter(c) {
+            Some(c) => result.push(c),
+            None => return None,
+        }
+    }
+
+    Some(result)
+}
+
+/// Convert a character to its corresponding Unicode superscript.
+fn to_superscript_codepoint(c: char) -> Option<char> {
+    char::from_u32(match c {
+        '0' => 0x2070,
+        '1' => 0x00B9,
+        '2' => 0x00B2,
+        '3' => 0x00B3,
+        '4' ..= '9' => 0x2070 + (c as u32 + 4 - '4' as u32),
+        '+' => 0x207A,
+        '-' => 0x207B,
+        '=' => 0x207C,
+        '(' => 0x207D,
+        ')' => 0x207E,
+        'n' => 0x207F,
+        'i' => 0x2071,
+        ' ' => 0x0020,
+        _ => return None,
+    })
+}
+
+/// Convert a character to its corresponding Unicode subscript.
+fn to_subscript_codepoint(c: char) -> Option<char> {
+    char::from_u32(match c {
+        '0' => 0x2080,
+        '1' ..= '9' => 0x2080 + (c as u32 - '0' as u32),
+        '+' => 0x208A,
+        '-' => 0x208B,
+        '=' => 0x208C,
+        '(' => 0x208D,
+        ')' => 0x208E,
+        'a' => 0x2090,
+        'e' => 0x2091,
+        'o' => 0x2092,
+        'x' => 0x2093,
+        'h' => 0x2095,
+        'k' => 0x2096,
+        'l' => 0x2097,
+        'm' => 0x2098,
+        'n' => 0x2099,
+        'p' => 0x209A,
+        's' => 0x209B,
+        't' => 0x209C,
+        ' ' => 0x0020,
+        _ => return None,
+    })
+}
+
+/// A category of script.
+pub type ScriptKind = usize;
+
+/// Text that is rendered smaller and raised, also known as superior.
+const SUPERSCRIPT: ScriptKind = 0;
+
+/// Text that is rendered smaller and lowered, also known as inferior.
+const SUBSCRIPT: ScriptKind = 1;