laser_pdf/text/

pieces.rs

use std::{
    borrow::{Borrow, Cow},
    cell::Cell,
    iter::Peekable,
};

use elsa::FrozenMap;
use icu_properties::LineBreak;
use icu_segmenter::LineBreakIteratorUtf8;

use crate::fonts::{Font, GeneralMetrics, ShapedGlyph};

struct TextPiecesCacheKey<'a> {
    text: Cow<'a, str>,
    font_index: usize,
    size: f32,
    color: u32,
    extra_character_spacing: f32,
    extra_word_spacing: f32,
    extra_line_height: f32,
}

#[derive(Hash, PartialEq, Eq)]
struct OwnedKey(TextPiecesCacheKey<'static>);

impl<'a> Borrow<TextPiecesCacheKey<'a>> for OwnedKey {
    fn borrow(&self) -> &TextPiecesCacheKey<'a> {
        &self.0
    }
}

impl<'a> PartialEq for TextPiecesCacheKey<'a> {
    fn eq(&self, other: &Self) -> bool {
        self.text == other.text
            && self.font_index == other.font_index
            && self.size.to_bits() == other.size.to_bits()
            && self.color == other.color
            && self.extra_character_spacing.to_bits() == other.extra_character_spacing.to_bits()
            && self.extra_word_spacing.to_bits() == other.extra_word_spacing.to_bits()
            && self.extra_line_height.to_bits() == other.extra_line_height.to_bits()
    }
}

impl<'a> Eq for TextPiecesCacheKey<'a> {}

impl<'a> std::hash::Hash for TextPiecesCacheKey<'a> {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.text.hash(state);
        self.font_index.hash(state);
        self.size.to_bits().hash(state);
        self.color.hash(state);
        self.extra_character_spacing.to_bits().hash(state);
        self.extra_word_spacing.to_bits().hash(state);
        self.extra_line_height.to_bits().hash(state);
    }
}

/// A data structure that holds cached text pieces (shaped and unicode-segmentend such that it is
/// ready for line breaking). This type gets passed around in the contexts and is needed by the
/// [crate::elements::text::Text] and [crate::elements::rich_text::RichText] elements. Currently
/// only [Self::new] is public for API stability reasons.
pub struct TextPiecesCache {
    line_segmenter: icu_segmenter::LineSegmenter,
    line_break_map:
        icu_properties::maps::CodePointMapDataBorrowed<'static, icu_properties::LineBreak>,
    cache: FrozenMap<OwnedKey, Vec<Piece>>,
    shape_buffer: Cell<Vec<(Option<usize>, ShapedGlyph)>>,
}

impl TextPiecesCache {
    pub fn new() -> Self {
        TextPiecesCache {
            line_segmenter: icu_segmenter::LineSegmenter::new_auto(),
            line_break_map: icu_properties::maps::line_break(),
            cache: FrozenMap::new(),
            shape_buffer: Cell::new(Vec::new()),
        }
    }

    pub(crate) fn pieces<'a, F: Font>(
        &'a self,
        text: &str,
        font: &F,
        size: f32,
        color: u32,
        extra_character_spacing: f32,
        extra_word_spacing: f32,
        extra_line_height: f32,
    ) -> &'a [Piece] {
        assert!(size.is_finite());
        assert!(extra_character_spacing.is_finite());
        assert!(extra_word_spacing.is_finite());
        assert!(extra_line_height.is_finite());

        let key = TextPiecesCacheKey {
            text: Cow::Borrowed(text),
            font_index: font.index(),
            size,
            color,
            extra_character_spacing,
            extra_word_spacing,
            extra_line_height,
        };

        if let Some(value) = self.cache.get(&key) {
            value
        } else {
            let shaped_hyphen = font.shape(super::HYPHEN, 0., 0.).next().unwrap();

            let mut shaped = self.shape_buffer.take();
            assert!(shaped.is_empty());

            super::shaping::shape(
                font,
                font.fallback_fonts(),
                None,
                text,
                extra_character_spacing / size,
                extra_word_spacing / size,
                &mut shaped,
                0,
            );

            let segments = self.line_segmenter.segment_str(text).peekable();

            let pieces = Pieces {
                current: Some(0),
                text,
                shaped: shaped.iter(),
                segments,
                shaped_hyphen,
                size,
                color,
                extra_line_height,
                main_font: font,
                main_font_metrics: font.general_metrics(),
                fallback_fonts: font.fallback_fonts(),
                line_break_map: &self.line_break_map,
            }
            .collect();

            shaped.clear();
            self.shape_buffer.set(shaped);

            self.cache.insert(
                OwnedKey(TextPiecesCacheKey {
                    text: Cow::Owned(text.to_string()),
                    ..key
                }),
                pieces,
            )
        }
    }
}

pub struct Piece {
    pub text: String,
    pub shaped: Vec<(Option<usize>, ShapedGlyph)>,

    /// The width of the main part of the piece. None means the piece consists only of whitespace.
    /// This is needed for line breaking to determine how to treat the piece if placed at the end
    /// of an overflowing line; a piece that consists only of whitespace can be placed there because
    /// trailing whitespace does not count towards the width of the line. It's not clear whether
    /// checking for zero would work for this as there might be fonts or specific shapings that
    /// contain characters with a width of zero but with a visible glyph. The `None` indicates that
    /// there are only glyphs in this piece that we count as whitespace.
    pub width: Option<f32>,

    pub height_above_baseline: f32,
    pub height_below_baseline: f32,
    pub trailing_whitespace_width: f32,

    /// Only applies when the piece is at the end of the line. Otherwise, it will not be counted
    /// towards the width and not displayed.
    pub trailing_hyphen: Option<(Option<usize>, ShapedGlyph)>,
    pub mandatory_break_after: bool,
    pub glyph_count: usize,
    pub empty: bool,
    pub size: f32,
    pub color: u32,
}

pub struct Pieces<'a, 'b, 'c, F> {
    current: Option<usize>,
    text: &'a str,
    shaped: std::slice::Iter<'c, (Option<usize>, ShapedGlyph)>,
    segments: Peekable<LineBreakIteratorUtf8<'b, 'a>>,
    main_font: &'a F,
    main_font_metrics: GeneralMetrics,
    fallback_fonts: &'a [F],
    shaped_hyphen: ShapedGlyph,
    size: f32,
    color: u32,
    extra_line_height: f32,
    line_break_map: &'a icu_properties::maps::CodePointMapDataBorrowed<'static, LineBreak>,
}

impl<'a, 'b, 'c, F: Font> Iterator for Pieces<'a, 'b, 'c, F> {
    type Item = Piece;

    fn next(&mut self) -> Option<Self::Item> {
        let mut shaped = self.shaped.clone();

        let Some(current) = self.current else {
            return None;
        };

        // TODO: Handle unsafe_to_break somewhere here. If unsafe_to_break is true when we would
        // otherwise split pieces we should probably fuse them into one piece because that seems
        // like the only reasonable thing to do.

        let segment = self.segments.find(|&s| s != 0).unwrap_or_else(|| {
            self.current = None;
            self.text.len()
        });

        let mut iter = std::iter::from_fn({
            let mut done = false;
            let shaped = &mut shaped;
            move || {
                if done {
                    return None;
                }

                let next = shaped.next()?;

                if next.1.text_range.end >= segment {
                    done = true;
                }

                Some(next)
            }
        })
        .peekable();

        let mut width = None;
        let mut whitespace_width = 0.;
        let mut glyph_count = 0;
        let mut mandatory_break_after = false;

        // A line and its the pieces is always at least as high as the main font. Otherwise empty
        // lines pieces would have no height. We could special case the empty line case, but that
        // would lead to the the possibility of an empty line being higher than a line that only has
        // glyphs from a fallback font.
        let mut height_above_baseline = self.main_font_metrics.height_above_baseline;
        let mut height_below_baseline = self.main_font_metrics.height_below_baseline;

        while let Some(glyph) = iter.next() {
            glyph_count += 1;

            // A space at the end of a line doesn't count towards the width.
            if matches!(
                &self.text[glyph.1.text_range.clone()],
                " " | "\u{00A0}" | "　"
            ) {
                whitespace_width += glyph.1.x_advance;
            } else if matches!(
                self.text[glyph.1.text_range.clone()]
                    .chars()
                    .next()
                    .map(|c| self.line_break_map.get(c)),
                Some(
                    LineBreak::MandatoryBreak
                        | LineBreak::CarriageReturn
                        | LineBreak::LineFeed
                        | LineBreak::NextLine,
                )
            ) {
                // We probably can't break here because the font might generate two missing glyphs
                // for a \r\n here.
                mandatory_break_after = true;
            } else {
                *width.get_or_insert(0.) += whitespace_width + glyph.1.x_advance;
                whitespace_width = 0.;
            }

            let font = glyph.0.map_or(self.main_font, |i| &self.fallback_fonts[i]);

            let metrics = font.general_metrics();

            height_above_baseline = height_above_baseline.max(metrics.height_above_baseline);
            height_below_baseline = height_below_baseline.max(metrics.height_below_baseline);
        }

        let text = &self.text[current..segment];

        // TODO: Handle the case of a soft hyphen followed by a space. Currently that just gets
        // ignored.
        let trailing_hyphen = text
            .ends_with('\u{00AD}')
            .then_some(self.shaped_hyphen.clone());

        let piece = Piece {
            text: text.to_string(),
            shaped: self
                .shaped
                .by_ref()
                .take(glyph_count)
                .map(|&(f, ref g)| {
                    (
                        f,
                        ShapedGlyph {
                            text_range: (g.text_range.start - current)
                                ..(g.text_range.end - current),
                            ..g.clone()
                        },
                    )
                })
                .collect(),
            width: width.map(|w| w * self.size),
            height_above_baseline: height_above_baseline * self.size,
            // TODO: Would it be better if this was only added to the below-baseline height of the
            // main font?
            height_below_baseline: height_below_baseline * self.size + self.extra_line_height,
            trailing_whitespace_width: whitespace_width * self.size,
            trailing_hyphen: trailing_hyphen.map(|glyph| (None, glyph)), // TODO: fallback if main font has no hyphen
            mandatory_break_after,
            glyph_count,

            // TODO: This might not work for \r\n, but that depends on the shaping. We should
            // proabably find a way to filter out newlines entirely so that they don't show up after
            // line breaking (and maybe also don't get shaped?).
            empty: glyph_count == 0 || (glyph_count == 1 && mandatory_break_after),

            size: self.size,
            color: self.color,
        };

        self.current = self.current.and(Some(segment));
        self.shaped = shaped;

        if self.segments.peek().is_none() && !mandatory_break_after {
            self.current = None;
        }

        Some(piece)
    }
}

#[cfg(test)]
mod tests {
    use crate::{fonts::ShapedGlyph, text::pieces::Piece};

    use super::*;

    #[derive(Debug)]
    struct FakeFont;

    #[derive(Clone, Debug)]
    struct FakeShaped<'a> {
        // last: usize,
        inner: std::str::CharIndices<'a>,
    }

    impl<'a> Iterator for FakeShaped<'a> {
        type Item = ShapedGlyph;

        fn next(&mut self) -> Option<Self::Item> {
            if let Some((i, c)) = self.inner.next() {
                Some(ShapedGlyph {
                    unsafe_to_break: false,
                    glyph_id: c as u32,
                    text_range: i..i + c.len_utf8(),
                    // we don't match newlines here because they produce the missing glyph which has
                    // a non-zero width.
                    x_advance_font: if matches!(c, '\u{00ad}') { 0. } else { 1. },
                    x_advance: if matches!(c, '\u{00ad}') { 0. } else { 1. },
                    x_offset: 0.,
                    y_offset: 0.,
                    y_advance: 0.,
                })
            } else {
                None
            }
        }
    }

    impl Font for FakeFont {
        type Shaped<'a>
            = FakeShaped<'a>
        where
            Self: 'a;

        fn shape<'a>(&'a self, text: &'a str, _: f32, _: f32) -> Self::Shaped<'a> {
            FakeShaped {
                inner: text.char_indices(),
            }
        }

        fn index(&self) -> usize {
            0
        }

        fn encode(&self, _: &mut crate::Pdf, _: u32, _: &str) -> crate::fonts::EncodedGlyph {
            unreachable!()
        }

        fn resource_name(&self) -> pdf_writer::Name<'_> {
            unreachable!()
        }

        fn general_metrics(&self) -> crate::fonts::GeneralMetrics {
            crate::fonts::GeneralMetrics {
                height_above_baseline: 0.5,
                height_below_baseline: 0.5,
            }
        }

        fn fallback_fonts(&self) -> &[Self] {
            &[]
        }
    }

    fn collect_piece<'a>(piece: &'a Piece) -> (&'a str, Option<f32>, f32, bool) {
        let mut text = String::new();

        for glyph in &piece.shaped {
            let character = glyph.1.glyph_id as u8 as char;

            assert_eq!(
                character.to_string(),
                piece.text[glyph.1.text_range.clone()]
            );

            text.push(glyph.1.glyph_id as u8 as char);
        }

        assert_eq!(text, piece.text);

        (
            &piece.text,
            piece.width,
            piece.trailing_whitespace_width,
            piece.mandatory_break_after,
        )
    }

    #[test]
    fn test_empty() {
        let text = "";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(&pieces, &[("", None, 0., false)]);
    }

    #[test]
    fn test_one() {
        let text = "abcde";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(&pieces, &[("abcde", Some(5.), 0., false)]);
    }

    #[test]
    fn test_two() {
        let text = "deadbeef defaced";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(
            &pieces,
            &[
                ("deadbeef ", Some(8.), 1., false),
                ("defaced", Some(7.), 0., false),
            ]
        );
    }

    #[test]
    fn test_three() {
        let text = "deadbeef defaced fart";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(
            &pieces,
            &[
                ("deadbeef ", Some(8.), 1., false),
                ("defaced ", Some(7.), 1., false),
                ("fart", Some(4.), 0., false)
            ],
        );
    }

    #[test]
    fn test_just_newline() {
        let text = "\n";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(&pieces, &[("\n", None, 0., true), ("", None, 0., false)]);
    }

    #[test]
    fn test_surrounded_newline() {
        let text = "abc\ndef";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(
            &pieces,
            &[("abc\n", Some(3.), 0., true), ("def", Some(3.), 0., false)]
        );
    }

    #[test]
    fn test_newline_at_start() {
        let text = "\nabc def";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(
            &pieces,
            &[
                ("\n", None, 0., true),
                ("abc ", Some(3.), 1., false),
                ("def", Some(3.), 0., false),
            ]
        );
    }

    #[test]
    fn test_trailing_newline() {
        let text = "abc def\n";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(
            &pieces,
            &[
                ("abc ", Some(3.), 1., false),
                ("def\n", Some(3.), 0., true),
                ("", None, 0., false),
            ]
        );
    }

    #[test]
    fn test_newline_after_space() {
        let text = "abc \ndef";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(
            &pieces,
            &[("abc \n", Some(3.), 1., true), ("def", Some(3.), 0., false)],
        );
    }

    #[test]
    fn test_trailing_soft_hyphen() {
        let text = "abc\u{ad}";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(&pieces, &[("abc\u{ad}", Some(3.), 0., false)]);
    }

    #[test]
    fn test_trailing_soft_hyphen_and_space() {
        let text = "abc\u{ad} ";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);

        let pieces: Vec<_> = pieces
            .iter()
            .map(|p| {
                let collected = collect_piece(p);

                (
                    collected.0,
                    collected.1,
                    collected.2,
                    collected.3,
                    p.trailing_hyphen.as_ref().map(|h| h.1.x_advance),
                )
            })
            .collect();

        assert_eq!(&pieces, &[("abc\u{ad} ", Some(3.), 1., false, None)]);
    }

    #[test]
    fn test_soft_hyphen_after_space() {
        let text = " \u{ad}abc";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(
            &pieces,
            &[
                (" ", None, 1., false),
                ("\u{ad}", Some(0.), 0., false),
                ("abc", Some(3.), 0., false),
            ],
        );
    }

    #[test]
    fn test_soft_hyphen_between_spaces() {
        let text = " \u{ad} ";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(
            &pieces,
            &[(" ", None, 1., false), ("\u{ad} ", Some(0.), 1., false)],
        );
    }

    #[test]
    fn test_just_spaces() {
        let text = "        ";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(&pieces, &[("        ", None, 8., false)]);
    }

    #[test]
    fn test_mixed_whitespace() {
        let text = "    abc    \ndef  the\tjflkdsa";

        let cache = TextPiecesCache::new();
        let pieces = cache.pieces(text, &FakeFont, 1., 0, 0., 0., 0.);
        let pieces: Vec<_> = pieces.iter().map(collect_piece).collect();

        assert_eq!(
            &pieces,
            &[
                ("    ", None, 4., false),
                // It's somewhat unclear whether the trailing spaces should count toward the
                // width here.
                ("abc    \n", Some(3.), 4., true),
                ("def  ", Some(3.), 2., false),
                ("the\t", Some(4.), 0., false),
                ("jflkdsa", Some(7.), 0., false),
            ],
        );
    }
}