ttj 1.1.4

Serialize OpenType tables to JSON
Documentation 
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/// Convert a font to a serialized JSON representation
pub mod context;
mod gdef;
pub mod jsondiff;
mod layout;
pub mod monkeypatching;
pub mod namemap;
mod serializefont;

use crate::{jsondiff::diff, serializefont::ToValue};
use context::SerializationContext;
use namemap::NameMap;
use read_fonts::{traversal::SomeTable, FontRef, TableProvider};
use serde_json::{Map, Value};
use skrifa::{charmap::Charmap, string::StringId, MetadataProvider};

pub use layout::gpos::just_kerns;

fn serialize_name_table<'a>(font: &(impl MetadataProvider<'a> + TableProvider<'a>)) -> Value {
    let mut map = Map::new();
    if let Ok(name) = font.name() {
        let mut ids: Vec<StringId> = name.name_record().iter().map(|x| x.name_id()).collect();
        ids.sort_by_key(|id| id.to_u16());
        for id in ids {
            let strings = font.localized_strings(id);
            if strings.clone().next().is_some() {
                let mut localized = Map::new();
                for string in font.localized_strings(id) {
                    localized.insert(
                        string.language().unwrap_or("default").to_string(),
                        Value::String(string.to_string()),
                    );
                }
                map.insert(id.to_string(), Value::Object(localized));
            }
        }
    }
    Value::Object(map)
}

fn serialize_cmap_table<'a>(font: &FontRef<'a>, names: &NameMap) -> Value {
    let charmap = Charmap::new(font);
    let mut map: Map<String, Value> = Map::new();
    for (codepoint, gid) in charmap.mappings() {
        let name = names.get(gid);
        map.insert(format!("U+{:04X}", codepoint), Value::String(name));
    }
    Value::Object(map)
}

fn serialize_hmtx_table<'a>(font: &impl TableProvider<'a>, names: &NameMap) -> Value {
    let mut map = Map::new();
    if let Ok(hmtx) = font.hmtx() {
        let widths = hmtx.h_metrics();
        let long_metrics = widths.len();
        for gid in 0..font.maxp().unwrap().num_glyphs() {
            let name = names.get(gid);
            if gid < (long_metrics as u16) {
                if let Some((width, lsb)) = widths
                    .get(gid as usize)
                    .map(|lm| (lm.advance(), lm.side_bearing()))
                {
                    map.insert(
                        name,
                        Value::Object(
                            vec![
                                ("width".to_string(), Value::Number(width.into())),
                                ("lsb".to_string(), Value::Number(lsb.into())),
                            ]
                            .into_iter()
                            .collect(),
                        ),
                    );
                }
            } else {
                // XXX
            }
        }
    }
    Value::Object(map)
}

/// Convert a font to a serialized JSON representation
///
/// This function is used to serialize a font to a JSON representation which can be compared with
/// another font. The JSON representation is a map of tables, where each table is represented as a
/// map of fields and values. The user of this function can also provide a glyph map, which is a
/// mapping from glyph IDs to glyph names. If the glyph map is not provided, the function will
/// attempt to create one from the font itself. (You may want to specify a glyph map from another
/// font to remove false positive differences if you are comparing two fonts which have the same glyph
/// order but the glyph names have changed, e.g. when development names have changed to production names.)
pub fn font_to_json(font: &FontRef, glyphmap: Option<&NameMap>) -> Value {
    let glyphmap = if let Some(glyphmap) = glyphmap {
        glyphmap
    } else {
        &NameMap::new(font)
    };
    let mut map = Map::new();
    // A serialization context bundles up all the information we need to serialize a font
    let context = SerializationContext::new(font, glyphmap.clone()).unwrap_or_else(|_| {
        panic!("Could not create serialization context for font");
    });

    // Some tables are serialized by using read_font's traversal feature; typically those which
    // are just a set of fields and values (or are so complicated we haven't yet been bothered
    // to write our own serializers for them...)
    for table in font.table_directory.table_records().iter() {
        let key = table.tag().to_string();
        let value = match table.tag().into_bytes().as_ref() {
            b"head" => font.head().map(|t| <dyn SomeTable>::serialize(&t)),
            b"hhea" => font.hhea().map(|t| <dyn SomeTable>::serialize(&t)),
            b"vhea" => font.vhea().map(|t| <dyn SomeTable>::serialize(&t)),
            b"vmtx" => font.vmtx().map(|t| <dyn SomeTable>::serialize(&t)),
            b"fvar" => font.fvar().map(|t| <dyn SomeTable>::serialize(&t)),
            b"avar" => font.avar().map(|t| <dyn SomeTable>::serialize(&t)),
            b"HVAR" => font.hvar().map(|t| <dyn SomeTable>::serialize(&t)),
            b"VVAR" => font.vvar().map(|t| <dyn SomeTable>::serialize(&t)),
            b"MVAR" => font.mvar().map(|t| <dyn SomeTable>::serialize(&t)),
            b"maxp" => font.maxp().map(|t| <dyn SomeTable>::serialize(&t)),
            b"OS/2" => font.os2().map(|t| <dyn SomeTable>::serialize(&t)),
            b"post" => font.post().map(|t| <dyn SomeTable>::serialize(&t)),
            b"loca" => font.loca(None).map(|t| <dyn SomeTable>::serialize(&t)),
            b"glyf" => font.glyf().map(|t| <dyn SomeTable>::serialize(&t)),
            b"gvar" => font.gvar().map(|t| <dyn SomeTable>::serialize(&t)),
            b"COLR" => font.colr().map(|t| <dyn SomeTable>::serialize(&t)),
            b"CPAL" => font.cpal().map(|t| <dyn SomeTable>::serialize(&t)),
            b"STAT" => font.stat().map(|t| <dyn SomeTable>::serialize(&t)),
            _ => font.expect_data_for_tag(table.tag()).map(|tabledata| {
                Value::Array(
                    tabledata
                        .as_ref()
                        .iter()
                        .map(|&x| Value::Number(x.into()))
                        .collect(),
                )
            }),
        };
        map.insert(
            key,
            value.unwrap_or_else(|_| Value::String("Could not parse".to_string())),
        );
    }

    // Other tables require a bit of massaging to produce information which makes sense to diff.
    map.insert("name".to_string(), serialize_name_table(font));
    map.insert("cmap".to_string(), serialize_cmap_table(font, glyphmap));
    map.insert("hmtx".to_string(), serialize_hmtx_table(font, glyphmap));
    map.insert("GDEF".to_string(), gdef::serialize_gdef_table(&context));
    map.insert("GPOS".to_string(), layout::serialize_gpos_table(&context));
    map.insert("GSUB".to_string(), layout::serialize_gsub_table(&context));
    Value::Object(map)
}

/// Compare two fonts and return a JSON representation of the differences
///
/// This function compares two fonts and returns a JSON representation of the differences between
/// them.
///
/// Arguments:
///
/// * `font_a` - The first font to compare
/// * `font_b` - The second font to compare
/// * `max_changes` - The maximum number of changes to report before giving up
/// * `no_match` - Don't try to match glyph names between fonts
pub fn table_diff(font_a: &FontRef, font_b: &FontRef, max_changes: usize, no_match: bool) -> Value {
    let glyphmap_a = NameMap::new(font_a);
    let glyphmap_b = NameMap::new(font_b);
    let big_difference = !no_match && !glyphmap_a.compatible(&glyphmap_b);

    #[cfg(not(target_family = "wasm"))]
    if big_difference {
        log::info!("Glyph names differ dramatically between fonts, using font names from font A");
    }

    let mut font_a_json = font_to_json(font_a, Some(&glyphmap_a));
    let mut font_b_json = font_to_json(
        font_b,
        Some(if big_difference {
            &glyphmap_a
        } else {
            &glyphmap_b
        }),
    );

    // Remove some tables which aren't useful
    font_a_json.as_object_mut().unwrap().remove("glyf");
    font_b_json.as_object_mut().unwrap().remove("glyf");
    font_a_json.as_object_mut().unwrap().remove("loca");
    font_b_json.as_object_mut().unwrap().remove("loca");

    diff(&font_a_json, &font_b_json, max_changes)
}

/// Compare two fonts and return a JSON representation of the differences in kerning
///
/// Arguments:
///
/// * `font_a` - The first font to compare
/// * `font_b` - The second font to compare
/// * `max_changes` - The maximum number of changes to report before giving up
/// * `no_match` - Don't try to match glyph names between fonts
pub fn kern_diff(font_a: &FontRef, font_b: &FontRef, max_changes: usize, no_match: bool) -> Value {
    let glyphmap_a = NameMap::new(font_a);
    let glyphmap_b = NameMap::new(font_b);
    let big_difference = !no_match && !glyphmap_a.compatible(&glyphmap_b);

    #[cfg(not(target_family = "wasm"))]
    if big_difference {
        log::info!("Glyph names differ dramatically between fonts, using font names from font A");
    }

    let kerns_a = just_kerns(font_to_json(font_a, None));
    // println!("Font A flat kerning: {:#?}", kerns_a);
    let kerns_b = just_kerns(font_to_json(
        font_b,
        Some(if big_difference {
            &glyphmap_a
        } else {
            &glyphmap_b
        }),
    ));
    // println!("Font B flat kerning: {:#?}", kerns_b);

    diff(&kerns_a, &kerns_b, max_changes)
}