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//! Character To Glyph Mapping
const font = @import("shared").font;
const sfnt = @import("shared").sfnt;
const constants = font.constants.charmap;
const FontError = font.errors.font.FontError;
const Reader = sfnt.types.reader.Reader;
const ENCODING_RECORD_SIZE: usize = 8;
pub fn select(table: []const u8) FontError![]const u8 {
var reader = Reader.initialize(table);
_ = try reader.readU16();
const record_count = try reader.readU16();
var best: ?[]const u8 = null;
var best_rank: u8 = 0;
var index: u16 = 0;
while (index < record_count) : (index += 1) {
try reader.seek(4 + @as(usize, index) * ENCODING_RECORD_SIZE);
const platform = try reader.readU16();
const encoding = try reader.readU16();
const offset = try reader.readU32();
if (offset >= table.len) {
continue;
}
const subtable = table[offset..];
var format_reader = Reader.initialize(subtable);
const format = try format_reader.readU16();
const rank = rankSubtable(platform, encoding, format);
if (rank > best_rank) {
best_rank = rank;
best = subtable;
}
}
return best orelse FontError.UnsupportedCharacterMap;
}
fn rankSubtable(platform: u16, encoding: u16, format: u16) u8 {
if (format == constants.FORMAT_SEGMENTED_COVERAGE) {
if (platform == constants.PLATFORM_WINDOWS and encoding == constants.ENCODING_WINDOWS_FULL) {
return 4;
}
if (platform == constants.PLATFORM_UNICODE) {
return 3;
}
}
if (format == constants.FORMAT_SEGMENT_MAPPING) {
if (platform == constants.PLATFORM_WINDOWS and encoding == constants.ENCODING_WINDOWS_BMP) {
return 2;
}
if (platform == constants.PLATFORM_UNICODE) {
return 1;
}
}
return 0;
}
pub fn lookup(subtable: []const u8, codepoint: u32) FontError!u16 {
var reader = Reader.initialize(subtable);
const format = try reader.readU16();
return switch (format) {
constants.FORMAT_SEGMENT_MAPPING => lookupSegmentMapping(subtable, codepoint),
constants.FORMAT_SEGMENTED_COVERAGE => lookupSegmentedCoverage(subtable, codepoint),
else => FontError.UnsupportedCharacterMap,
};
}
fn lookupSegmentMapping(subtable: []const u8, codepoint: u32) FontError!u16 {
if (codepoint > 0xFFFF) {
return constants.MISSING_GLYPH;
}
const character: u16 = @truncate(codepoint);
var reader = Reader.initialize(subtable);
try reader.seek(6);
const segment_count_doubled = try reader.readU16();
const segment_count = segment_count_doubled / 2;
const end_codes: usize = 14;
const start_codes: usize = end_codes + segment_count_doubled + 2;
const deltas: usize = start_codes + segment_count_doubled;
const range_offsets: usize = deltas + segment_count_doubled;
var segment: u16 = 0;
while (segment < segment_count) : (segment += 1) {
try reader.seek(end_codes + @as(usize, segment) * 2);
const end_code = try reader.readU16();
if (character > end_code) {
continue;
}
try reader.seek(start_codes + @as(usize, segment) * 2);
const start_code = try reader.readU16();
if (character < start_code) {
return constants.MISSING_GLYPH;
}
try reader.seek(deltas + @as(usize, segment) * 2);
const delta = try reader.readU16();
const range_offset_position = range_offsets + @as(usize, segment) * 2;
try reader.seek(range_offset_position);
const range_offset = try reader.readU16();
if (range_offset == 0) {
return character +% delta;
}
const glyph_position = range_offset_position + @as(usize, range_offset) +
@as(usize, character - start_code) * 2;
try reader.seek(glyph_position);
const glyph = try reader.readU16();
if (glyph == constants.MISSING_GLYPH) {
return constants.MISSING_GLYPH;
}
return glyph +% delta;
}
return constants.MISSING_GLYPH;
}
fn lookupSegmentedCoverage(subtable: []const u8, codepoint: u32) FontError!u16 {
var reader = Reader.initialize(subtable);
try reader.seek(12);
const group_count = try reader.readU32();
const groups: usize = 16;
const GROUP_SIZE: usize = 12;
var low: u32 = 0;
var high: u32 = group_count;
while (low < high) {
const middle = low + (high - low) / 2;
try reader.seek(groups + @as(usize, middle) * GROUP_SIZE);
const start_character = try reader.readU32();
const end_character = try reader.readU32();
const start_glyph = try reader.readU32();
if (codepoint < start_character) {
high = middle;
} else if (codepoint > end_character) {
low = middle + 1;
} else {
return @truncate(start_glyph + (codepoint - start_character));
}
}
return constants.MISSING_GLYPH;
}
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