true_type_font.hpp

// Copyright Take Vos 2019-2022.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "font.hpp"
#include "otype_sfnt.hpp"
#include "otype_kern.hpp"
#include "font_char_map.hpp"
#include "../file/file_view.hpp"
#include "../graphic_path.hpp"
#include "../counters.hpp"
#include "../utility/module.hpp"
#include <memory>
#include <filesystem>
 
namespace hi::inline v1 {
 
class true_type_font final : public font {
public:
    true_type_font(std::filesystem::path const& path) : _path(path), _view(file_view{path})
    {
        ++global_counter<"ttf:map">;
        try {
            _bytes = as_span<std::byte const>(_view);
            parse_font_directory(_bytes);
 
            // Clear the view to reclaim resources.
            _view = {};
            _bytes = {};
            ++global_counter<"ttf:unmap">;
 
        } catch (std::exception const& e) {
            throw parse_error(std::format("{}: Could not parse font directory.\n{}", path.string(), e.what()));
        }
    }
 
    true_type_font() = delete;
    true_type_font(true_type_font const& other) = delete;
    true_type_font& operator=(true_type_font const& other) = delete;
    true_type_font(true_type_font&& other) = delete;
    true_type_font& operator=(true_type_font&& other) = delete;
    ~true_type_font() = default;
 
    [[nodiscard]] bool loaded() const noexcept override
    {
        return to_bool(_view);
    }
 
    [[nodiscard]] graphic_path get_path(hi::glyph_id glyph_id) const override;
    [[nodiscard]] float get_advance(hi::glyph_id glyph_id) const override;
    [[nodiscard]] glyph_metrics get_metrics(hi::glyph_id glyph_id) const override;
    [[nodiscard]] shape_run_result_type shape_run(iso_639 language, iso_15924 script, gstring run) const override;
 
private:
    std::filesystem::path _path;
 
    mutable file_view _view;
 
    float OS2_x_height = 0;
    float OS2_cap_height = 0;
 
    float _em_scale;
 
    uint16_t _num_horizontal_metrics;
 
    int num_glyphs;
    mutable std::span<std::byte const> _bytes;
    mutable std::span<std::byte const> _loca_table_bytes;
    mutable std::span<std::byte const> _glyf_table_bytes;
    mutable std::span<std::byte const> _hmtx_table_bytes;
    mutable std::span<std::byte const> _kern_table_bytes;
    mutable std::span<std::byte const> _GSUB_table_bytes;
    bool _loca_is_offset32;
 
    void cache_tables(std::span<std::byte const> bytes) const
    {
        _loca_table_bytes = otype_sfnt_search<"loca">(bytes);
        _glyf_table_bytes = otype_sfnt_search<"glyf">(bytes);
        _hmtx_table_bytes = otype_sfnt_search<"hmtx">(bytes);
 
        // Optional tables.
        _kern_table_bytes = otype_sfnt_search<"kern">(bytes);
        _GSUB_table_bytes = otype_sfnt_search<"GSUB">(bytes);
    }
 
    void load_view() const noexcept
    {
        if (_view) {
            [[likely]] return;
        }
 
        _view = file_view{_path};
        _bytes = as_span<std::byte const>(_view);
        ++global_counter<"ttf:map">;
        cache_tables(_bytes);
    }
 
    void parse_font_directory(std::span<std::byte const> bytes);
 
    [[nodiscard]] std::ptrdiff_t get_coverage_index(std::span<std::byte const> bytes, hi::glyph_id glyph);
 
    [[nodiscard]] font::shape_run_result_type shape_run_basic(gstring run) const;
 
    void shape_run_kern(font::shape_run_result_type &shape_result) const;
};
 
} // namespace hi::inline v1