otype_coverage.hpp

// Copyright Take Vos 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 "../geometry/geometry.hpp"
#include "../telemetry/telemetry.hpp"
#include "../utility/utility.hpp"
#include "../parser/parser.hpp"
#include <cstddef>
#include <span>
 
hi_export_module(hikogui.font.otype_coverage);
 
hi_export namespace hi::inline v1 {
 
struct coverage_format1 {
    big_int16_buf_t coverage_format;
    big_int16_buf_t glyph_count;
};
 
struct coverage_format2 {
    big_int16_buf_t coverage_format;
    big_int16_buf_t range_count;
};
 
struct coverage_format2_range {
    big_int16_buf_t start_glyph_id;
    big_int16_buf_t end_glyph_id;
    big_int16_buf_t start_coverage_index;
};
 
[[nodiscard]] std::ptrdiff_t true_type_font::get_coverage_index(std::span<std::byte const> bytes, hi::glyph_id glyph_id)
{
    std::size_t offset = 0;
 
    hi_assert_or_return(*glyph_id >= 0 && *glyph_id < num_glyphs, -2);
 
    auto const header1 = make_placement_ptr<coverage_format1>(bytes, offset);
    if (*header1->coverage_format == 1) {
        auto const table = make_placement_array<big_uint16_buf_t>(bytes, offset, *header1->glyph_count);
 
        auto const it = std::lower_bound(table.begin(), table.end(), glyph_id, [](auto const &item, auto const &value) {
            return *item < *value;
        });
 
        if (it != table.end() and **it == *glyph_id) {
            return std::distance(table.begin(), it);
        } else {
            return -1;
        }
 
    } else if (*header1->coverage_format == 2) {
        offset = 0;
        auto const header2 = make_placement_ptr<coverage_format2>(bytes, offset);
 
        auto const table = make_placement_array<coverage_format2_range>(bytes, offset, *header2->range_count);
 
        auto const it = std::lower_bound(table.begin(), table.end(), glyph_id, [](auto const &item, auto const &value) {
            return *item.end_glyph_id < *value;
        });
 
        if (it != table.end() and *it->start_glyph_id <= *glyph_id and *glyph_id <= *it->end_glyph_id) {
            return *it->start_coverage_index + *glyph_id - *it->start_glyph_id;
        } else {
            return -1;
        }
 
    } else {
        return -2;
    }
}
 
} // namespace hi::inline v1