mirror of
https://github.com/xiaoqidun/ofdgo.git
synced 2026-10-29 16:59:27 +08:00
341 lines
11 KiB
Go
341 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 ofdgo
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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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"maps"
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"slices"
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"unicode/utf16"
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"unicode/utf8"
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"github.com/xiaoqidun/pdfgo"
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)
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// pdfImportedFont 保存单次导入共用的字体资源、度量及源字形映射，不保存文档标识
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type pdfImportedFont struct {
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resource *FontResource
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checksum [32]byte
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metrics FontMetrics
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type1Glyphs map[string]uint16
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repairLimit uint16
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}
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// importedFont 按原PDF字体复用包装和解析结果，失败结果不进入缓存
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// 入参: source 源字体
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// 返回: *pdfImportedFont 只读导入字体, error 字体程序或后端错误
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func (p *pdfImporter) importedFont(source *pdfgo.Font) (*pdfImportedFont, error) {
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if cached := p.fonts[source]; cached != nil {
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return cached, nil
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}
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var type1 *type1Program
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result := &pdfImportedFont{}
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if source.ProgramType == "FontFile" {
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parsed, err := parseType1Program(source.Program)
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if err != nil {
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return nil, fmt.Errorf("PDF font %s program: %w", source.Name, err)
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}
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type1 = &parsed
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result.type1Glyphs = parsed.glyphIDs()
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}
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program, limit, err := pdfFontProgram(source, type1)
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if err != nil {
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return nil, fmt.Errorf("PDF font %s program: %w", source.Name, err)
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}
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if p.editor.backends.FontResources == nil {
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return nil, fmt.Errorf("PDF font %s resource: font resources: %w", source.Name, ErrBackendUnavailable)
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}
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result.resource, err = p.editor.backends.FontResources.OpenFontResource(FontFile{Name: source.Name + ".ttf", Data: program}, 0)
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if err != nil {
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return nil, fmt.Errorf("PDF font %s resource: %w", source.Name, err)
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}
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if p.editor.backends.Fonts == nil {
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return nil, fmt.Errorf("PDF font backend unavailable")
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}
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result.metrics, err = p.editor.backends.Fonts.OpenFont(result.resource.Data)
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if err != nil {
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return nil, fmt.Errorf("PDF font %s metrics: %w", source.Name, err)
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}
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if _, ok := result.metrics.(FontOutlines); !ok {
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return nil, fmt.Errorf("PDF font backend does not provide glyph outlines")
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}
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result.checksum, result.repairLimit = sha256.Sum256(result.resource.Data), limit
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if p.fonts == nil {
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p.fonts = make(map[*pdfgo.Font]*pdfImportedFont)
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}
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p.fonts[source] = result
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return result, nil
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}
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// pdfFontProgram 为PDF子集字体补齐封装表，保留字形轮廓和编号
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// 复合字体的重复映射区段按PDF字符映射重建，不改变CID对应的字形
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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, uint16 缺失度量前的完整字形数, error 错误信息
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func pdfFontProgram(source *pdfgo.Font, type1 *type1Program) ([]byte, uint16, error) {
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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 := parseType1Program(program)
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if err != nil {
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return nil, 0, 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(pdfFontIdentity(source))
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if err != nil {
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return nil, 0, 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 = wrapCFFToOTF(program)
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if err != nil {
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return nil, 0, err
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}
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}
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tables, err := fontFileTables(program, 0)
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if err != nil {
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return nil, 0, 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, 0, 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, 0, fmt.Errorf("embedded PDF font has no glyphs")
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}
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changed := false
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var repairedLimit uint16
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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, 0, 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, 0, 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 := pdfMissingLeftBearings(tables, limit, int(count))
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if err != nil {
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return nil, 0, err
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}
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tables["hmtx"] = append(bytes.Clone(tables["hmtx"]), missing...)
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repairedLimit = 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 := 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"] = 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 || pdfCmapOverlaps(tables["cmap"])) {
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mapping := map[rune]uint16{}
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for _, code := range slices.Sorted(maps.Keys(source.Unicode)) {
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glyphs, err := source.Decode([]byte(code))
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if err != nil {
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return nil, 0, err
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}
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if len(glyphs) != 1 || !glyphs[0].HasID {
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return nil, 0, &pdfgo.UnsupportedError{Feature: "font without explicit glyph mapping"}
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}
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glyph := glyphs[0]
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if glyph.ID >= count {
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return nil, 0, fmt.Errorf("PDF font glyph %d exceeds glyph count %d", glyph.ID, count)
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}
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if utf8.RuneCountInString(glyph.Text) == 1 {
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char, _ := utf8.DecodeRuneInString(glyph.Text)
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if _, exists := mapping[char]; !exists {
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mapping[char] = glyph.ID
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}
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}
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}
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addPackedGlyphMapping(mapping, count)
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tables["cmap"] = buildCmapTable(count, mapping)
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changed = true
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}
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if len(fontNamesFromTable(tables["name"])) == 0 {
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fontName := pdfFontIdentity(source)
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name := utf16.Encode([]rune(fontName))
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if len(name) > 32767 {
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return nil, 0, 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"] = 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"] = 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 && !pdfSFNTMissingPadding(program) {
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return program, repairedLimit, nil
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}
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result, err := serializeOTF(tables)
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return result, repairedLimit, err
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}
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// pdfFontIdentity 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 pdfFontIdentity(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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// pdfCmapOverlaps 检查格式4字符映射是否包含交叠区段
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// 入参: data cmap表数据
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// 返回: bool 是否存在交叠
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func pdfCmapOverlaps(data []byte) bool {
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if len(data) < 4 {
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return false
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}
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count := int(binary.BigEndian.Uint16(data[2:]))
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if count > (len(data)-4)/8 {
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return false
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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(len(data)) || uint64(len(data))-offset < 16 {
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continue
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}
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sub := data[int(offset):]
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if binary.BigEndian.Uint16(sub) != 4 {
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continue
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}
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length := int(binary.BigEndian.Uint16(sub[2:]))
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segments := int(binary.BigEndian.Uint16(sub[6:])) / 2
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if length > len(sub) || 16+8*segments > length {
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continue
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}
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for i := 1; i < segments; i++ {
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previous := binary.BigEndian.Uint16(sub[14+2*(i-1):])
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start := binary.BigEndian.Uint16(sub[16+2*segments+2*i:])
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if start <= previous {
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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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// pdfSFNTMissingPadding 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 pdfSFNTMissingPadding(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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// pdfMissingLeftBearings 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 pdfMissingLeftBearings(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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