typst/src/export/pdf/font.rs

use std::collections::BTreeMap;

use ecow::format_eco;
use pdf_writer::types::{CidFontType, FontFlags, SystemInfo, UnicodeCmap};
use pdf_writer::{Filter, Finish, Name, Rect, Str};
use ttf_parser::{name_id, GlyphId, Tag};

use super::{deflate, EmExt, PdfContext, RefExt};
use crate::util::SliceExt;

/// Embed all used fonts into the PDF.
pub fn write_fonts(ctx: &mut PdfContext) {
    for font in ctx.font_map.items() {
        let type0_ref = ctx.alloc.bump();
        let cid_ref = ctx.alloc.bump();
        let descriptor_ref = ctx.alloc.bump();
        let cmap_ref = ctx.alloc.bump();
        let data_ref = ctx.alloc.bump();
        ctx.font_refs.push(type0_ref);

        let glyphs = &ctx.glyph_sets[font];
        let metrics = font.metrics();
        let ttf = font.ttf();

        let postscript_name = font
            .find_name(name_id::POST_SCRIPT_NAME)
            .unwrap_or_else(|| "unknown".to_string());

        let base_font = format_eco!("ABCDEF+{}", postscript_name);
        let base_font = Name(base_font.as_bytes());
        let cmap_name = Name(b"Custom");
        let system_info = SystemInfo {
            registry: Str(b"Adobe"),
            ordering: Str(b"Identity"),
            supplement: 0,
        };

        // Write the base font object referencing the CID font.
        ctx.writer
            .type0_font(type0_ref)
            .base_font(base_font)
            .encoding_predefined(Name(b"Identity-H"))
            .descendant_font(cid_ref)
            .to_unicode(cmap_ref);

        // Check for the presence of CFF outlines to select the correct
        // CID-Font subtype.
        let subtype = match ttf
            .raw_face()
            .table(Tag::from_bytes(b"CFF "))
            .or(ttf.raw_face().table(Tag::from_bytes(b"CFF2")))
        {
            Some(_) => CidFontType::Type0,
            None => CidFontType::Type2,
        };

        // Write the CID font referencing the font descriptor.
        let mut cid = ctx.writer.cid_font(cid_ref);
        cid.subtype(subtype);
        cid.base_font(base_font);
        cid.system_info(system_info);
        cid.font_descriptor(descriptor_ref);
        cid.default_width(0.0);

        if subtype == CidFontType::Type2 {
            cid.cid_to_gid_map_predefined(Name(b"Identity"));
        }

        // Extract the widths of all glyphs.
        let num_glyphs = ttf.number_of_glyphs();
        let mut widths = vec![0.0; num_glyphs as usize];
        for &g in glyphs {
            let x = ttf.glyph_hor_advance(GlyphId(g)).unwrap_or(0);
            widths[g as usize] = font.to_em(x).to_font_units();
        }

        // Write all non-zero glyph widths.
        let mut first = 0;
        let mut width_writer = cid.widths();
        for (w, group) in widths.group_by_key(|&w| w) {
            let end = first + group.len();
            if w != 0.0 {
                let last = end - 1;
                width_writer.same(first as u16, last as u16, w);
            }
            first = end;
        }

        width_writer.finish();
        cid.finish();

        let mut flags = FontFlags::empty();
        flags.set(FontFlags::SERIF, postscript_name.contains("Serif"));
        flags.set(FontFlags::FIXED_PITCH, ttf.is_monospaced());
        flags.set(FontFlags::ITALIC, ttf.is_italic());
        flags.insert(FontFlags::SYMBOLIC);
        flags.insert(FontFlags::SMALL_CAP);

        let global_bbox = ttf.global_bounding_box();
        let bbox = Rect::new(
            font.to_em(global_bbox.x_min).to_font_units(),
            font.to_em(global_bbox.y_min).to_font_units(),
            font.to_em(global_bbox.x_max).to_font_units(),
            font.to_em(global_bbox.y_max).to_font_units(),
        );

        let italic_angle = ttf.italic_angle().unwrap_or(0.0);
        let ascender = metrics.ascender.to_font_units();
        let descender = metrics.descender.to_font_units();
        let cap_height = metrics.cap_height.to_font_units();
        let stem_v = 10.0 + 0.244 * (f32::from(ttf.weight().to_number()) - 50.0);

        // Write the font descriptor (contains metrics about the font).
        let mut font_descriptor = ctx.writer.font_descriptor(descriptor_ref);
        font_descriptor
            .name(base_font)
            .flags(flags)
            .bbox(bbox)
            .italic_angle(italic_angle)
            .ascent(ascender)
            .descent(descender)
            .cap_height(cap_height)
            .stem_v(stem_v);

        match subtype {
            CidFontType::Type0 => font_descriptor.font_file3(data_ref),
            CidFontType::Type2 => font_descriptor.font_file2(data_ref),
        };

        font_descriptor.finish();

        // Compute a reverse mapping from glyphs to unicode.
        let cmap = {
            let mut mapping = BTreeMap::new();
            for subtable in
                ttf.tables().cmap.into_iter().flat_map(|table| table.subtables)
            {
                if subtable.is_unicode() {
                    subtable.codepoints(|n| {
                        if let Some(c) = std::char::from_u32(n) {
                            if let Some(GlyphId(g)) = ttf.glyph_index(c) {
                                if glyphs.contains(&g) {
                                    mapping.insert(g, c);
                                }
                            }
                        }
                    });
                }
            }

            let mut cmap = UnicodeCmap::new(cmap_name, system_info);
            for (g, c) in mapping {
                cmap.pair(g, c);
            }
            cmap
        };

        // Write the /ToUnicode character map, which maps glyph ids back to
        // unicode codepoints to enable copying out of the PDF.
        ctx.writer
            .cmap(cmap_ref, &deflate(&cmap.finish()))
            .filter(Filter::FlateDecode);

        // Subset and write the font's bytes.
        let data = font.data();
        let subsetted = {
            let glyphs: Vec<_> = glyphs.iter().copied().collect();
            let profile = subsetter::Profile::pdf(&glyphs);
            subsetter::subset(data, font.index(), profile)
        };

        // Compress and write the font's byte.
        let data = subsetted.as_deref().unwrap_or(data);
        let data = deflate(data);
        let mut stream = ctx.writer.stream(data_ref, &data);
        stream.filter(Filter::FlateDecode);

        if subtype == CidFontType::Type0 {
            stream.pair(Name(b"Subtype"), Name(b"OpenType"));
        }

        stream.finish();
    }
}