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-//! Super-basic text shaping.
-//!
-//! This is really only suited for simple Latin text. It picks the most suitable
-//! font for each individual character. When the direction is right-to-left, the
-//! word is spelled backwards. Vertical shaping is not supported.
-
-use std::fmt::{self, Debug, Display, Formatter};
-
-use fontdock::{FaceId, FaceQuery, FallbackTree, FontVariant};
-use ttf_parser::{Face, GlyphId};
-
-use crate::font::FontLoader;
-use crate::geom::{Dir, Length, Point, Size};
-use crate::layout::{Element, Frame};
-
-/// A shaped run of text.
-#[derive(Clone, PartialEq)]
-pub struct Shaped {
- /// The shaped text.
- pub text: String,
- /// The font face the text was shaped with.
- pub face: FaceId,
- /// The shaped glyphs.
- pub glyphs: Vec<GlyphId>,
- /// The horizontal offsets of the glyphs. This is indexed parallel to
- /// `glyphs`. Vertical offsets are not yet supported.
- pub offsets: Vec<Length>,
- /// The font size.
- pub font_size: Length,
-}
-
-impl Shaped {
- /// Create a new shape run with empty `text`, `glyphs` and `offsets`.
- pub fn new(face: FaceId, font_size: Length) -> Self {
- Self {
- text: String::new(),
- face,
- glyphs: vec![],
- offsets: vec![],
- font_size,
- }
- }
-
- /// Encode the glyph ids into a big-endian byte buffer.
- pub fn encode_glyphs_be(&self) -> Vec<u8> {
- let mut bytes = Vec::with_capacity(2 * self.glyphs.len());
- for &GlyphId(g) in &self.glyphs {
- bytes.push((g >> 8) as u8);
- bytes.push((g & 0xff) as u8);
- }
- bytes
- }
-}
-
-impl Debug for Shaped {
- fn fmt(&self, f: &mut Formatter) -> fmt::Result {
- write!(f, "Shaped({})", self.text)
- }
-}
-
-/// Identifies a vertical metric of a font.
-#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
-pub enum VerticalFontMetric {
- /// The distance from the baseline to the typographic ascender.
- ///
- /// Corresponds to the typographic ascender from the `OS/2` table if present
- /// and falls back to the ascender from the `hhea` table otherwise.
- Ascender,
- /// The approximate height of uppercase letters.
- CapHeight,
- /// The approximate height of non-ascending lowercase letters.
- XHeight,
- /// The baseline on which the letters rest.
- Baseline,
- /// The distance from the baseline to the typographic descender.
- ///
- /// Corresponds to the typographic descender from the `OS/2` table if
- /// present and falls back to the descender from the `hhea` table otherwise.
- Descender,
-}
-
-impl Display for VerticalFontMetric {
- fn fmt(&self, f: &mut Formatter) -> fmt::Result {
- f.pad(match self {
- Self::Ascender => "ascender",
- Self::CapHeight => "cap-height",
- Self::XHeight => "x-height",
- Self::Baseline => "baseline",
- Self::Descender => "descender",
- })
- }
-}
-
-/// Shape text into a frame containing [`Shaped`] runs.
-pub fn shape(
- text: &str,
- dir: Dir,
- fallback: &FallbackTree,
- variant: FontVariant,
- font_size: Length,
- top_edge: VerticalFontMetric,
- bottom_edge: VerticalFontMetric,
- loader: &mut FontLoader,
-) -> Frame {
- let mut frame = Frame::new(Size::new(Length::ZERO, Length::ZERO));
- let mut shaped = Shaped::new(FaceId::MAX, font_size);
- let mut width = Length::ZERO;
- let mut top = Length::ZERO;
- let mut bottom = Length::ZERO;
-
- // Create an iterator with conditional direction.
- let mut forwards = text.chars();
- let mut backwards = text.chars().rev();
- let chars: &mut dyn Iterator<Item = char> = if dir.is_positive() {
- &mut forwards
- } else {
- &mut backwards
- };
-
- for c in chars {
- let query = FaceQuery { fallback: fallback.iter(), variant, c };
- if let Some(id) = loader.query(query) {
- let face = loader.face(id).get();
- let (glyph, glyph_width) = match lookup_glyph(face, c) {
- Some(v) => v,
- None => continue,
- };
-
- let units_per_em = f64::from(face.units_per_em().unwrap_or(1000));
- let convert = |units| units / units_per_em * font_size;
-
- // Flush the buffer and reset the metrics if we use a new font face.
- if shaped.face != id {
- place(&mut frame, shaped, width, top, bottom);
-
- shaped = Shaped::new(id, font_size);
- width = Length::ZERO;
- top = convert(f64::from(lookup_metric(face, top_edge)));
- bottom = convert(f64::from(lookup_metric(face, bottom_edge)));
- }
-
- shaped.text.push(c);
- shaped.glyphs.push(glyph);
- shaped.offsets.push(width);
- width += convert(f64::from(glyph_width));
- }
- }
-
- place(&mut frame, shaped, width, top, bottom);
-
- frame
-}
-
-/// Place shaped text into a frame.
-fn place(frame: &mut Frame, shaped: Shaped, width: Length, top: Length, bottom: Length) {
- if !shaped.text.is_empty() {
- frame.push(Point::new(frame.size.width, top), Element::Text(shaped));
- frame.size.width += width;
- frame.size.height = frame.size.height.max(top - bottom);
- }
-}
-
-/// Look up the glyph for `c` and returns its index alongside its advance width.
-fn lookup_glyph(face: &Face, c: char) -> Option<(GlyphId, u16)> {
- let glyph = face.glyph_index(c)?;
- let width = face.glyph_hor_advance(glyph)?;
- Some((glyph, width))
-}
-
-/// Look up a vertical metric.
-fn lookup_metric(face: &Face, metric: VerticalFontMetric) -> i16 {
- match metric {
- VerticalFontMetric::Ascender => lookup_ascender(face),
- VerticalFontMetric::CapHeight => face
- .capital_height()
- .filter(|&h| h > 0)
- .unwrap_or_else(|| lookup_ascender(face)),
- VerticalFontMetric::XHeight => face
- .x_height()
- .filter(|&h| h > 0)
- .unwrap_or_else(|| lookup_ascender(face)),
- VerticalFontMetric::Baseline => 0,
- VerticalFontMetric::Descender => lookup_descender(face),
- }
-}
-
-/// The ascender of the face.
-fn lookup_ascender(face: &Face) -> i16 {
- // We prefer the typographic ascender over the Windows ascender because
- // it can be overly large if the font has large glyphs.
- face.typographic_ascender().unwrap_or_else(|| face.ascender())
-}
-
-/// The descender of the face.
-fn lookup_descender(face: &Face) -> i16 {
- // See `lookup_ascender` for reason.
- face.typographic_descender().unwrap_or_else(|| face.descender())
-}