mirror of
https://github.com/xiaoqidun/ofdgo.git
synced 2026-10-30 01:27:26 +08:00
339 lines
11 KiB
Go
339 lines
11 KiB
Go
// 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 pdf
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import (
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"bytes"
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"crypto/sha256"
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"encoding/binary"
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"fmt"
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"unicode/utf16"
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basefont "github.com/xiaoqidun/ofdgo/internal/base/font"
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"github.com/xiaoqidun/pdfgo"
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)
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// FontRepair 保存字体封装修复范围，不混用字形度量与位置索引
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type FontRepair struct {
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MetricsLimit uint16
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Locations bool
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}
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// EmbeddedFontName 去除标准六位大写子集前缀，保留字体名称和样式后缀
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// 入参: name PDF或内嵌字体名称
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// 返回: string 原字体名称
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func EmbeddedFontName(name string) string {
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if len(name) <= 7 || name[6] != '+' {
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return name
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}
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for i := range 6 {
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if name[i] < 'A' || name[i] > 'Z' {
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return name
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}
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}
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return name[7:]
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}
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// FontProgram 为PDF子集字体补齐封装表，保留字形轮廓和编号
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// 无效字符表按PDF已解码字形重建，不改变字符对应的字形编号
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// 入参: source PDF字体, type1 已解析的Type1程序，nil时按需解析
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// 返回: []byte 封装后的字体数据, FontRepair 字体修复范围, error 错误信息
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func FontProgram(source *pdfgo.Font, type1 *basefont.Type1Program) ([]byte, FontRepair, error) {
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var repair FontRepair
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program := source.Program
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if source.ProgramType == "FontFile" {
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if type1 == nil {
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parsed, err := basefont.ParseType1Program(program)
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if err != nil {
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return nil, repair, err
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}
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type1 = &parsed
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}
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var err error
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program, err = type1.ToCFF(FontIdentity(source))
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if err != nil {
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return nil, repair, err
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}
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}
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bareCFF := len(program) >= 4 && program[0] == 1 && program[1] == 0 && program[2] >= 4 && program[3] >= 1 && program[3] <= 4
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if source.ProgramType == "Type1C" || source.ProgramType == "CIDFontType0C" || bareCFF {
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var err error
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program, _, err = basefont.WrapCFFToOTF(program)
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if err != nil {
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return nil, repair, err
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}
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}
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tables, err := basefont.FileTables(program, 0)
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if err != nil {
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return nil, repair, err
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}
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if len(tables["head"]) < 54 || len(tables["maxp"]) < 6 || len(tables["hhea"]) < 36 || len(tables["hmtx"]) == 0 {
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return nil, repair, fmt.Errorf("embedded PDF font lacks required metrics")
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}
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count := binary.BigEndian.Uint16(tables["maxp"][4:6])
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if count == 0 {
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return nil, repair, fmt.Errorf("embedded PDF font has no glyphs")
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}
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repair.Locations, err = basefont.NormalizeTrueTypeLocations(tables)
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if err != nil {
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return nil, repair, err
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}
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changed := repair.Locations
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if head := tables["head"]; len(head) == 56 && binary.BigEndian.Uint32(head[:4]) == 0x00010000 && head[54] == 0 && head[55] == 0 {
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tables["head"] = head[:54]
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changed = true
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}
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if cff := tables["CFF "]; len(cff) != 0 {
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sanitized, err := basefont.SanitizeCFF(cff)
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if err != nil {
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return nil, repair, err
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}
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normalized, err := basefont.NormalizeCFFCharstringsAt(sanitized, binary.BigEndian.Uint16(tables["head"][18:20]))
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if err != nil {
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return nil, repair, err
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}
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if !bytes.Equal(normalized, cff) {
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tables["CFF "] = normalized
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changed = true
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}
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}
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metrics := int(binary.BigEndian.Uint16(tables["hhea"][34:36]))
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if metrics == 0 || metrics > int(count) {
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return nil, repair, fmt.Errorf("invalid embedded PDF font metric count")
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}
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metricLength := 4*metrics + 2*(int(count)-metrics)
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if len(tables["hmtx"]) < metricLength {
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if len(tables["hmtx"]) < 4*metrics || len(tables["hmtx"])%2 != 0 {
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return nil, repair, fmt.Errorf("incomplete embedded PDF font metrics: have %d, need %d", len(tables["hmtx"]), metricLength)
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}
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limit := metrics + (len(tables["hmtx"])-4*metrics)/2
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missing, err := missingLeftBearings(tables, limit, int(count))
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if err != nil {
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return nil, repair, err
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}
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tables["hmtx"] = append(bytes.Clone(tables["hmtx"]), missing...)
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repair.MetricsLimit = uint16(limit)
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changed = true
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}
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if len(tables["hmtx"]) > metricLength {
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tables["hmtx"] = tables["hmtx"][:metricLength]
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changed = true
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}
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invalidCmap := false
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if source.Subtype == "TrueType" || source.Subtype == "Type0" {
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mapping := basefont.ParseCmapMappings(tables["cmap"])
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for char, glyph := range mapping {
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if glyph >= count {
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delete(mapping, char)
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invalidCmap = true
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}
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}
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if invalidCmap && source.Subtype == "TrueType" {
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tables["cmap"] = basefont.BuildCmapTable(count, mapping)
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changed = true
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}
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}
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if len(tables["cmap"]) == 0 || source.Subtype == "Type0" && invalidCmap || (source.Subtype == "Type0" || source.Subtype == "TrueType") && CmapNeedsRebuild(tables["cmap"]) {
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mapping, err := source.GlyphMap()
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if err != nil {
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return nil, repair, err
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}
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for _, glyph := range mapping {
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if glyph >= count {
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return nil, repair, fmt.Errorf("PDF font glyph %d exceeds glyph count %d", glyph, count)
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}
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}
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basefont.AddPackedGlyphMapping(mapping, count)
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tables["cmap"] = basefont.BuildCmapTable(count, mapping)
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changed = true
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}
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if len(basefont.NamesFromTable(tables["name"])) == 0 {
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fontName := FontIdentity(source)
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name := utf16.Encode([]rune(fontName))
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if len(name) > 32767 {
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return nil, repair, fmt.Errorf("PDF font name exceeds name table capacity")
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}
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data := make([]byte, 42+len(name)*2)
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binary.BigEndian.PutUint16(data[2:], 3)
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binary.BigEndian.PutUint16(data[4:], 42)
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for n, id := range []uint16{1, 4, 6} {
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record := data[6+n*12:]
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binary.BigEndian.PutUint16(record, 3)
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binary.BigEndian.PutUint16(record[2:], 1)
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binary.BigEndian.PutUint16(record[4:], 0x409)
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binary.BigEndian.PutUint16(record[6:], id)
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binary.BigEndian.PutUint16(record[8:], uint16(len(name)*2))
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}
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for n, v := range name {
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binary.BigEndian.PutUint16(data[42+n*2:], v)
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}
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tables["name"] = data
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changed = true
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}
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if len(tables["post"]) == 0 {
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tables["post"] = basefont.BuildPostTable()
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changed = true
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}
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if len(tables["OS/2"]) == 0 {
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hhea := tables["hhea"]
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tables["OS/2"] = basefont.BuildOS2TableWithMetrics(int16(binary.BigEndian.Uint16(hhea[4:6])), int16(binary.BigEndian.Uint16(hhea[6:8])))
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changed = true
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}
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for _, tag := range []string{"cvt ", "fpgm", "prep"} {
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if data, ok := tables[tag]; ok && len(data) == 0 {
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delete(tables, tag)
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changed = true
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}
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}
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if !changed && !sfntMissingPadding(program) {
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return program, repair, nil
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}
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result, err := basefont.SerializeOTF(tables)
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return result, repair, err
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}
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// FontIdentity 返回字体名称或由原始程序生成的稳定封装标识
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// 入参: source PDF字体
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// 返回: string 字体标识
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func FontIdentity(source *pdfgo.Font) string {
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if source.Name != "" {
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return source.Name
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}
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checksum := sha256.Sum256(source.Program)
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return fmt.Sprintf("PDF-%x", checksum[:28])
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}
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// CmapNeedsRebuild 检查字体封装字符表是否存在结构错误或交叠区段
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// 入参: data cmap表数据
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// 返回: bool 是否需要按PDF显式字形编号重建
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func CmapNeedsRebuild(data []byte) bool {
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if len(data) < 4 || binary.BigEndian.Uint16(data) != 0 {
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return true
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}
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count := int(binary.BigEndian.Uint16(data[2:]))
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if count == 0 || count > (len(data)-4)/8 {
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return true
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}
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for index := range count {
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offset := uint64(binary.BigEndian.Uint32(data[8+8*index:]))
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if offset < uint64(4+8*count) || offset > uint64(len(data)) || uint64(len(data))-offset < 2 {
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return true
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}
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sub := data[int(offset):]
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if binary.BigEndian.Uint16(sub) == 6 {
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if len(sub) < 10 {
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return true
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}
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length := int(binary.BigEndian.Uint16(sub[2:]))
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first, glyphs := int(binary.BigEndian.Uint16(sub[6:])), int(binary.BigEndian.Uint16(sub[8:]))
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if length%2 != 0 || length > len(sub) || 10+2*glyphs > length || first+glyphs > 65536 {
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return true
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}
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continue
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}
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if binary.BigEndian.Uint16(sub) != 4 {
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continue
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}
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if len(sub) < 16 {
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return true
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}
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length := int(binary.BigEndian.Uint16(sub[2:]))
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segmentBytes := int(binary.BigEndian.Uint16(sub[6:]))
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segments := segmentBytes / 2
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if segmentBytes == 0 || segmentBytes%2 != 0 || length%2 != 0 || length > len(sub) || 16+8*segments > length {
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return true
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}
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glyphStart := 16 + 8*segments
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previous := -1
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for i := 0; i < segments; i++ {
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end := int(binary.BigEndian.Uint16(sub[14+2*i:]))
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start := int(binary.BigEndian.Uint16(sub[16+2*segments+2*i:]))
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if end < start || start <= previous || i == segments-1 && (start != 65535 || end != 65535) {
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return true
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}
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previous = end
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position := 16 + 6*segments + 2*i
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offset := int(binary.BigEndian.Uint16(sub[position:]))
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if offset != 0 && (offset%2 != 0 || position+offset < glyphStart || position+offset+2*(end-start+1) > length) {
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return true
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}
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}
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}
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return false
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}
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// sfntMissingPadding 判断字体表目录是否引用了未写入的末尾对齐字节
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// 入参: program OpenType字体数据
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// 返回: bool 是否需要重新封装
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func sfntMissingPadding(program []byte) bool {
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if len(program) < 12 {
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return true
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}
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count := int(binary.BigEndian.Uint16(program[4:6]))
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if count > (len(program)-12)/16 {
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return true
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}
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for index := range count {
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record := program[12+16*index:]
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offset := int(binary.BigEndian.Uint32(record[8:12]))
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length := int(binary.BigEndian.Uint32(record[12:16]))
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if offset > len(program) || length > len(program)-offset || (4-length%4)%4 > len(program)-offset-length {
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return true
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}
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}
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return false
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}
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// missingLeftBearings 从轮廓边界恢复缺失的尾部左侧边距
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// 入参: tables 字体表, start 首个缺失字形, count 字形总数
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// 返回: []byte 补齐的hmtx数据, error 无法读取轮廓
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func missingLeftBearings(tables map[string][]byte, start, count int) ([]byte, error) {
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head, loca, glyf := tables["head"], tables["loca"], tables["glyf"]
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if len(head) < 54 || len(glyf) == 0 {
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return nil, fmt.Errorf("embedded PDF font lacks glyph outlines for missing metrics")
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}
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format := int(int16(binary.BigEndian.Uint16(head[50:52])))
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entrySize := 2
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if format == 1 {
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entrySize = 4
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} else if format != 0 {
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return nil, fmt.Errorf("invalid embedded PDF font location format")
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}
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if len(loca) < (count+1)*entrySize {
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return nil, fmt.Errorf("incomplete embedded PDF font glyph locations")
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}
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location := func(index int) int {
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if format == 0 {
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return int(binary.BigEndian.Uint16(loca[index*2:])) * 2
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}
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return int(binary.BigEndian.Uint32(loca[index*4:]))
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}
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result := make([]byte, 2*(count-start))
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for index := start; index < count; index++ {
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from, to := location(index), location(index+1)
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if from > to || to > len(glyf) {
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return nil, fmt.Errorf("invalid embedded PDF font glyph location")
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}
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if from == to {
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continue
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}
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if to-from < 10 {
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return nil, fmt.Errorf("incomplete embedded PDF font glyph outline")
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}
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copy(result[(index-start)*2:], glyf[from+2:from+4])
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}
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return result, nil
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}
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