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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 ofdgo
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import (
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"encoding/binary"
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"maps"
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"slices"
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"unicode/utf8"
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"github.com/go-text/typesetting/font/opentype/tables"
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)
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// subsetCmapVariations 裁剪Unicode变体映射，将非默认变体的字形加入保留集合
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// 入参: data 字符映射表, chars 使用字符, glyphs 保留字形, count 字形总数
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// 返回: []byte 格式14子表，无变体时为空, bool 映射是否有效
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func subsetCmapVariations(data []byte, chars map[rune]bool, glyphs map[uint16]bool, count uint16) ([]byte, bool) {
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if len(data) < 4 {
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return nil, false
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}
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n := int(binary.BigEndian.Uint16(data[2:]))
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if n > (len(data)-4)/8 {
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return nil, false
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}
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var source []byte
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for i := 0; i < n; i++ {
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record := data[4+i*8:]
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offset := uint64(binary.BigEndian.Uint32(record[4:]))
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if offset < uint64(4+n*8) || offset+2 > uint64(len(data)) {
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return nil, false
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}
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if binary.BigEndian.Uint16(data[offset:]) != 14 {
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continue
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}
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if source != nil || binary.BigEndian.Uint16(record) != 0 || binary.BigEndian.Uint16(record[2:]) != 5 || offset+10 > uint64(len(data)) {
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return nil, false
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}
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length := uint64(binary.BigEndian.Uint32(data[offset+2:]))
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if length < 10 || offset+length > uint64(len(data)) {
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return nil, false
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}
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source = data[offset : offset+length]
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}
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if source == nil {
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return nil, true
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}
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return subsetCmapVariationTable(source, chars, glyphs, count)
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}
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// subsetCmapVariationTable 按使用字符筛选默认及非默认变体，保持选择符和映射有序
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// 入参: data 格式14子表, chars 使用字符, glyphs 保留字形, count 字形总数
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// 返回: []byte 裁剪后的子表, bool 子表是否有效
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func subsetCmapVariationTable(data []byte, chars map[rune]bool, glyphs map[uint16]bool, count uint16) ([]byte, bool) {
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n := uint64(binary.BigEndian.Uint32(data[6:]))
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header := 10 + n*11
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if header > uint64(len(data)) {
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return nil, false
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}
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used := slices.Sorted(maps.Keys(chars))
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var records, payload []byte
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previous := rune(-1)
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for i := uint64(0); i < n; i++ {
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raw := data[10+i*11:]
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for j, size := range []uint64{4, 5} {
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offset := uint64(binary.BigEndian.Uint32(raw[3+j*4:]))
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if offset == 0 {
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continue
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}
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if offset < header || offset+4 > uint64(len(data)) {
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return nil, false
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}
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entries := uint64(binary.BigEndian.Uint32(data[offset:]))
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if offset+4+entries*size > uint64(len(data)) {
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return nil, false
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}
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}
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record, _, err := tables.ParseVariationSelector(raw, data)
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selector := cmapVariationRune(record.VarSelector)
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if err != nil || !utf8.ValidRune(selector) || selector <= previous || !validCmapVariation(record, count) {
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return nil, false
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}
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previous = selector
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if !chars[selector] {
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continue
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}
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defaults := subsetCmapDefaultVariations(record.DefaultUVS.Ranges, used)
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var alternatives []byte
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for _, entry := range record.NonDefaultUVS.Ranges {
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if chars[cmapVariationRune(entry.UnicodeValue)] {
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alternatives = append(alternatives, entry.UnicodeValue[:]...)
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alternatives = binary.BigEndian.AppendUint16(alternatives, uint16(entry.GlyphID))
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glyphs[uint16(entry.GlyphID)] = true
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}
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}
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if len(defaults)+len(alternatives) == 0 {
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continue
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}
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start := len(records)
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records = append(records, record.VarSelector[:]...)
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records = append(records, make([]byte, 8)...)
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for j, entries := range [][]byte{defaults, alternatives} {
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if len(entries) == 0 {
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continue
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}
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binary.BigEndian.PutUint32(records[start+3+j*4:], uint32(len(payload)+1))
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payload = binary.BigEndian.AppendUint32(payload, uint32(len(entries)/(4+j)))
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payload = append(payload, entries...)
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}
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}
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if len(records) == 0 {
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return nil, true
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}
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if uint64(len(records))+uint64(len(payload))+10 > 1<<32-1 {
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return nil, false
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}
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for i := 0; i < len(records); i += 11 {
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for _, j := range []int{3, 7} {
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offset := binary.BigEndian.Uint32(records[i+j:])
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if offset != 0 {
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binary.BigEndian.PutUint32(records[i+j:], offset-1+uint32(10+len(records)))
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}
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}
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}
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out := make([]byte, 10, 10+len(records)+len(payload))
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binary.BigEndian.PutUint16(out, 14)
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binary.BigEndian.PutUint32(out[2:], uint32(cap(out)))
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binary.BigEndian.PutUint32(out[6:], uint32(len(records)/11))
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out = append(out, records...)
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return append(out, payload...), true
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}
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// validCmapVariation 检查变体映射的字符范围、排序、互斥关系及字形编号
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// 入参: record 选择符记录, count 字形总数
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// 返回: bool 映射是否有效
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func validCmapVariation(record tables.VariationSelector, count uint16) bool {
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defaults := record.DefaultUVS.Ranges
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previous := rune(-1)
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for _, entry := range defaults {
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first := cmapVariationRune(entry.StartUnicodeValue)
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last := first + rune(entry.AdditionalCount)
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if first <= previous || !utf8.ValidRune(first) || !utf8.ValidRune(last) || first < 0xd800 && last >= 0xd800 {
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return false
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}
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previous = last
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}
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previous = -1
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index := 0
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for _, entry := range record.NonDefaultUVS.Ranges {
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char := cmapVariationRune(entry.UnicodeValue)
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if char <= previous || !utf8.ValidRune(char) || uint16(entry.GlyphID) >= count {
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return false
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}
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previous = char
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for index < len(defaults) && cmapVariationRune(defaults[index].StartUnicodeValue)+rune(defaults[index].AdditionalCount) < char {
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index++
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}
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if index < len(defaults) && cmapVariationRune(defaults[index].StartUnicodeValue) <= char {
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return false
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}
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}
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return true
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}
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// subsetCmapDefaultVariations 筛选默认变体的使用字符，将连续字符合并为格式14范围
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// 入参: ranges 默认变体范围, chars 已排序的使用字符
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// 返回: []byte 范围记录，不含数量字段
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func subsetCmapDefaultVariations(ranges []tables.UnicodeRange, chars []rune) []byte {
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var out []byte
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index := 0
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last := rune(-2)
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for _, char := range chars {
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for index < len(ranges) && cmapVariationRune(ranges[index].StartUnicodeValue)+rune(ranges[index].AdditionalCount) < char {
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index++
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}
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if index == len(ranges) {
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break
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}
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if cmapVariationRune(ranges[index].StartUnicodeValue) > char {
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continue
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}
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if char == last+1 && out[len(out)-1] < 255 {
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out[len(out)-1]++
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} else {
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out = append(out, byte(char>>16), byte(char>>8), byte(char), 0)
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}
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last = char
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}
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return out
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}
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// cmapVariationRune 读取变体映射中的24位Unicode码点
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// 入参: value 三字节码点
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// 返回: rune Unicode码点
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func cmapVariationRune(value [3]byte) rune {
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return rune(value[0])<<16 | rune(value[1])<<8 | rune(value[2])
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}
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// buildCmapWithVariations 在生成的Unicode映射中插入格式14记录，保持编码记录有序
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// 入参: count 字形总数, mapping 字符映射, variations 格式14子表
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// 返回: []byte 字符映射表
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func buildCmapWithVariations(count uint16, mapping map[rune]uint16, variations []byte) []byte {
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base := buildCmapTable(count, mapping)
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if len(variations) == 0 {
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return base
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}
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payload := base[binary.BigEndian.Uint32(base[8:]):]
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out := make([]byte, 28, 28+len(payload)+len(variations))
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binary.BigEndian.PutUint16(out[2:], 3)
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encoding := uint16(3)
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if binary.BigEndian.Uint16(payload) == 12 {
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encoding = 4
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}
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binary.BigEndian.PutUint16(out[6:], encoding)
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binary.BigEndian.PutUint32(out[8:], 28)
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binary.BigEndian.PutUint16(out[14:], 5)
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binary.BigEndian.PutUint32(out[16:], uint32(28+len(payload)))
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last := 4 + 8*(int(binary.BigEndian.Uint16(base[2:]))-1)
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copy(out[20:28], base[last:last+8])
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binary.BigEndian.PutUint32(out[24:], 28)
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out = append(out, payload...)
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return append(out, variations...)
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}
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