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// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package font
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import (
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"encoding/binary"
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"fmt"
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"maps"
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"sort"
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"sync"
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"github.com/go-text/typesetting/font/opentype/tables"
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)
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// SFNT 保存独立字体表和基础度量，不包含绘图库对象
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type SFNT struct {
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Tables map[string][]byte
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IsTrueType, IsCFF bool
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cmaps []sfntCmap
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units, count, horizontal, vertical uint16
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reverseOnce sync.Once
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reverse map[uint16][]rune
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}
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// sfntCmap 保存编码记录及对应字符映射
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type sfntCmap struct {
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platform, encoding, format uint16
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mapping map[rune]uint16
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}
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// ParseSFNT 校验独立字体的必需表、度量范围及字符映射
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// 入参: data 独立SFNT数据
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// 返回: *SFNT 字体, error 格式错误
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func ParseSFNT(data []byte) (*SFNT, error) {
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table, err := FileTables(data, 0)
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if err != nil {
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return nil, err
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}
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return ParseSFNTTables(table)
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}
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// ParseSFNTTables 校验字体表并解析度量和字符映射，借用表数据且不修改其内容
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// 入参: table 字体表
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// 返回: *SFNT 字体, error 格式错误
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func ParseSFNTTables(table map[string][]byte) (*SFNT, error) {
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head, maxp, hhea := table["head"], table["maxp"], table["hhea"]
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if len(head) != 54 || len(maxp) < 6 || len(hhea) < 36 {
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return nil, fmt.Errorf("missing or truncated font metrics")
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}
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f := &SFNT{Tables: maps.Clone(table), IsTrueType: table["glyf"] != nil, IsCFF: table["CFF "] != nil}
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f.units, f.count = binary.BigEndian.Uint16(head[18:]), binary.BigEndian.Uint16(maxp[4:])
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f.horizontal = binary.BigEndian.Uint16(hhea[34:])
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if f.units < 16 || f.units > 16384 || f.count == 0 || f.IsTrueType == f.IsCFF || !validSFNTMetrics(table["hmtx"], f.count, f.horizontal) {
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return nil, fmt.Errorf("invalid font outlines or horizontal metrics")
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}
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if vhea := table["vhea"]; vhea != nil {
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if len(vhea) < 36 {
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return nil, fmt.Errorf("truncated vertical metrics header")
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}
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f.vertical = binary.BigEndian.Uint16(vhea[34:])
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if !validSFNTMetrics(table["vmtx"], f.count, f.vertical) {
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return nil, fmt.Errorf("invalid vertical metrics")
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}
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}
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if f.IsTrueType {
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format := binary.BigEndian.Uint16(head[50:])
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if format > 1 || len(table["loca"]) < (int(f.count)+1)*(2+2*int(format)) {
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return nil, fmt.Errorf("invalid glyph location table")
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}
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}
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cmaps, err := readSFNTCmaps(table["cmap"])
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if err != nil {
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return nil, err
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}
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f.cmaps = cmaps
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for _, cmap := range f.cmaps {
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for _, glyph := range cmap.mapping {
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if glyph >= f.count {
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return nil, fmt.Errorf("cmap glyph index out of range")
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}
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}
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}
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return f, nil
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}
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// validSFNTMetrics 校验完整度量记录和末尾边距数组的范围
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// 入参: data 度量表, count 字形数, metrics 完整度量记录数
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// 返回: bool 是否有效
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func validSFNTMetrics(data []byte, count, metrics uint16) bool {
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return metrics != 0 && metrics <= count && len(data) >= int(metrics)*4+int(count-metrics)*2
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}
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// readSFNTCmaps 校验各编码子表并保留原顺序，共享子表只解析一次
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// 入参: data cmap表
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// 返回: []sfntCmap 编码记录, error 表结构错误
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func readSFNTCmaps(data []byte) ([]sfntCmap, error) {
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data, err := NormalizeCmap(data)
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if err != nil {
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return nil, err
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}
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if _, _, err := tables.ParseCmap(data); err != nil {
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return nil, err
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}
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count := int(binary.BigEndian.Uint16(data[2:]))
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result := make([]sfntCmap, 0, count)
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parsed := make(map[uint32]map[rune]uint16)
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for i := range count {
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record := data[4+8*i:]
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offset := binary.BigEndian.Uint32(record[4:])
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if uint64(offset)+2 > uint64(len(data)) {
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return nil, fmt.Errorf("invalid cmap offset")
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}
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sub := data[offset:]
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format := binary.BigEndian.Uint16(sub)
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mapping, found := parsed[offset]
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if !found {
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mapping = make(map[rune]uint16)
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var err error
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switch format {
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case 0:
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parseCmapFormat0(sub, mapping)
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case 4:
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parseCmapFormat4(sub, mapping)
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case 6:
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parseCmapFormat6(sub, mapping)
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case 12:
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parseCmapFormat12(sub, mapping)
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case 2:
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mapping, err = parseCmapFormat2(sub)
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case 8, 10, 13:
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mapping, err = parseCmapExtended(sub)
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case 14:
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default:
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return nil, fmt.Errorf("unsupported cmap format %d", format)
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}
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if err != nil {
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return nil, err
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}
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parsed[offset] = mapping
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}
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result = append(result, sfntCmap{binary.BigEndian.Uint16(record), binary.BigEndian.Uint16(record[2:]), format, mapping})
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}
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return result, nil
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}
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// UnitsPerEm 返回字体设计单位
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// 返回: uint16 每em单位数
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func (f *SFNT) UnitsPerEm() uint16 { return f.units }
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// NumGlyphs 返回字形总数
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// 返回: uint16 字形数
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func (f *SFNT) NumGlyphs() uint16 { return f.count }
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// CmapEntries 返回各编码记录的映射项总数，共享子表按记录分别计数
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// 返回: int 用于缓存预算的映射项数量
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func (f *SFNT) CmapEntries() int {
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count := 0
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for _, cmap := range f.cmaps {
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count += len(cmap.mapping)
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}
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return count
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}
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// GlyphIndex 按编码表顺序查找字符，不替换缺失字形
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// 入参: char 字符
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// 返回: uint16 字形编号
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func (f *SFNT) GlyphIndex(char rune) uint16 {
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for _, cmap := range f.cmaps {
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if gid := cmap.mapping[char]; gid != 0 {
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return gid
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}
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}
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return 0
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}
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// glyphCharacters 返回指向指定字形的全部字符
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// 入参: gid 字形编号
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// 返回: []rune 排序后的字符
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func (f *SFNT) glyphCharacters(gid uint16) []rune {
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f.reverseOnce.Do(func() {
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f.reverse = make(map[uint16][]rune)
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seen := make(map[rune]bool)
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for _, cmap := range f.cmaps {
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for char, glyph := range cmap.mapping {
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if glyph != 0 && !seen[char] {
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f.reverse[glyph] = append(f.reverse[glyph], char)
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seen[char] = true
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}
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}
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}
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for _, chars := range f.reverse {
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sort.Slice(chars, func(i, j int) bool { return chars[i] < chars[j] })
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}
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})
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return f.reverse[gid]
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}
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// GlyphAdvance 返回水平字宽
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// 入参: gid 字形编号
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// 返回: uint16 字宽
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func (f *SFNT) GlyphAdvance(gid uint16) uint16 {
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if gid >= f.count {
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return 0
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}
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return binary.BigEndian.Uint16(f.Tables["hmtx"][int(min(gid, f.horizontal-1))*4:])
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}
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// GlyphVerticalAdvance 返回纵向字距，无垂直度量时使用em高度
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// 入参: gid 字形编号
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// 返回: uint16 纵向字距
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func (f *SFNT) GlyphVerticalAdvance(gid uint16) uint16 {
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if f.vertical == 0 {
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return f.units
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}
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if gid >= f.count {
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return 0
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}
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return binary.BigEndian.Uint16(f.Tables["vmtx"][int(min(gid, f.vertical-1))*4:])
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}
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// sideBearing 返回指定方向的字形边距
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// 入参: gid 字形编号, vertical 是否读取顶部边距
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// 返回: int16 边距
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func (f *SFNT) sideBearing(gid uint16, vertical bool) int16 {
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data, count := f.Tables["hmtx"], f.horizontal
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if vertical {
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data, count = f.Tables["vmtx"], f.vertical
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}
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if count == 0 || gid >= f.count {
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return 0
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}
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offset := int(gid)*4 + 2
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if gid >= count {
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offset = int(count)*4 + int(gid-count)*2
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}
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return int16(binary.BigEndian.Uint16(data[offset:]))
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}
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// VerticalMetrics 依据OS/2排版标志选择行度量，缺失时使用hhea
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// 返回: uint16 上升高度, uint16 下降高度, uint16 行间隙
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func (f *SFNT) VerticalMetrics() (uint16, uint16, uint16) {
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hhea, os2 := f.Tables["hhea"], f.Tables["OS/2"]
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a, d, gap := int(int16(binary.BigEndian.Uint16(hhea[4:]))), int(int16(binary.BigEndian.Uint16(hhea[6:]))), int(int16(binary.BigEndian.Uint16(hhea[8:])))
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if len(os2) >= 78 {
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if binary.BigEndian.Uint16(os2[62:])&0x80 != 0 {
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ta, td := int(int16(binary.BigEndian.Uint16(os2[68:]))), int(int16(binary.BigEndian.Uint16(os2[70:])))
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if ta > 0 && td < 0 {
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a, d, gap = ta, td, int(int16(binary.BigEndian.Uint16(os2[72:])))
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}
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} else {
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wa, wd := int(binary.BigEndian.Uint16(os2[74:])), int(binary.BigEndian.Uint16(os2[76:]))
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if wa != 0 && wd != 0 {
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gap, a, d = a-d+gap-wa-wd, wa, -wd
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}
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}
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}
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return uint16(max(0, a)), uint16(max(0, -d)), uint16(min(65535, max(0, gap)))
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}
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// Write 保留原始表数据并重新计算字体校验和
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// 返回: []byte 独立字体
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func (f *SFNT) Write() []byte { data, _ := SerializeOTF(f.Tables); return data }
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// glyphDependencies 批量收集复合字形依赖，校验引用、记录长度和嵌套深度
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// 入参: glyphs 字形编号
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// 返回: []uint16 依赖字形, error 字形错误
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func (f *SFNT) glyphDependencies(glyphs ...uint16) ([]uint16, error) {
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heights, active := make(map[uint16]int), make(map[uint16]bool)
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var result []uint16
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var visit func(uint16) error
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visit = func(id uint16) error {
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if id >= f.count || active[id] || len(active) > 64 {
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return fmt.Errorf("invalid composite glyph reference")
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}
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if height := heights[id]; height != 0 {
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if len(active)+height > 65 {
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return fmt.Errorf("invalid composite glyph reference")
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}
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return nil
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}
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heights[id], active[id] = 1, true
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defer delete(active, id)
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data, err := trueTypeGlyphData(f.Tables, id)
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if err != nil {
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return err
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}
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if len(data) == 0 {
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return nil
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}
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if len(data) < 10 {
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return fmt.Errorf("truncated glyph header")
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}
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if int16(binary.BigEndian.Uint16(data)) >= 0 {
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return nil
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}
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for pos := 10; ; {
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if len(data)-pos < 4 {
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return fmt.Errorf("truncated composite glyph")
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}
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flags, child := binary.BigEndian.Uint16(data[pos:]), binary.BigEndian.Uint16(data[pos+2:])
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pos += 6
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if flags&1 != 0 {
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pos += 2
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}
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switch flags & 0xc8 {
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case 8:
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pos += 2
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case 0x40:
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pos += 4
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case 0x80:
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pos += 8
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case 0:
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default:
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return fmt.Errorf("invalid composite transform")
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}
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if pos > len(data) {
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return fmt.Errorf("truncated composite transform")
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}
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if heights[child] == 0 {
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result = append(result, child)
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}
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if err := visit(child); err != nil {
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return err
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}
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heights[id] = max(heights[id], heights[child]+1)
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if flags&0x20 == 0 {
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break
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}
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}
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return nil
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}
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for _, id := range glyphs {
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if err := visit(id); err != nil {
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return nil, err
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}
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}
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return result, nil
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}
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