mirror of
https://github.com/xiaoqidun/ofdgo.git
synced 2026-10-29 14:53:44 +08:00
348 lines
12 KiB
Go
348 lines
12 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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"encoding/binary"
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"fmt"
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"sort"
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)
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// otfTableRecord OTF表记录结构
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// 字段: tag 标签, checksum 校验和, offset 偏移, length 长度, data 数据
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type otfTableRecord struct {
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tag string
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checksum uint32
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offset int
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length int
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data []byte
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}
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// extractCollectionFont 提取集合中的单个OpenType字体，保留表内容并重新计算校验和
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// 入参: data 集合数据, index 字体索引
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// 返回: []byte 单字体数据, error 错误信息
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func extractCollectionFont(data []byte, index int) ([]byte, error) {
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tables, err := fontFileTables(data, index)
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if err != nil {
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return nil, err
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}
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if len(tables["head"]) < 12 {
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return nil, fmt.Errorf("invalid head font table")
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}
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tables["head"] = bytes.Clone(tables["head"])
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clear(tables["head"][8:12])
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return serializeOTF(tables)
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}
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// fontFileTables 读取单字体或集合指定项的表目录，不复制表数据
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// 入参: data 字体数据, index 字体索引
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// 返回: map[string][]byte 字体表, error 错误信息
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func fontFileTables(data []byte, index int) (map[string][]byte, error) {
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count, err := fontFileCount(data)
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if err != nil {
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return nil, err
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}
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if index < 0 || index >= count {
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return nil, fmt.Errorf("invalid font index %d", index)
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}
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var offset uint64
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if string(data[:4]) == "ttcf" {
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offset = uint64(binary.BigEndian.Uint32(data[12+index*4:]))
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}
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if offset > uint64(len(data)-12) {
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return nil, fmt.Errorf("invalid font offset")
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}
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header := data[offset : offset+12]
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if string(header[:4]) != "\x00\x01\x00\x00" && string(header[:4]) != "OTTO" && string(header[:4]) != "true" {
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return nil, fmt.Errorf("invalid OpenType header")
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}
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tableCount := uint64(binary.BigEndian.Uint16(header[4:]))
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offset += 12
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if tableCount == 0 || tableCount > (uint64(len(data))-offset)/16 {
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return nil, fmt.Errorf("invalid font table directory")
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}
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tables := make(map[string][]byte, tableCount)
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for i := uint64(0); i < tableCount; i++ {
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entry := data[offset+i*16 : offset+(i+1)*16]
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tag := string(entry[:4])
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start := uint64(binary.BigEndian.Uint32(entry[8:]))
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length := uint64(binary.BigEndian.Uint32(entry[12:]))
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if start > uint64(len(data)) || length > uint64(len(data))-start {
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return nil, fmt.Errorf("invalid %s font table range", tag)
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}
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if _, exists := tables[tag]; exists {
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return nil, fmt.Errorf("duplicate %s font table", tag)
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}
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tables[tag] = data[start : start+length]
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}
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return tables, nil
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}
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// calcTableChecksum 计算字体表校验和
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// 入参: data 表数据
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// 返回: uint32 校验和
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func calcTableChecksum(data []byte) uint32 {
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var sum uint32
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length := len(data)
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for i := 0; i < length; i += 4 {
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if i+4 <= length {
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sum += binary.BigEndian.Uint32(data[i : i+4])
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} else {
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var val uint32
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rem := data[i:]
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for j, b := range rem {
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val |= uint32(b) << (24 - 8*j)
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}
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sum += val
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}
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}
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return sum
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}
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// buildHeadTable 构建head表
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// 入参: unitsPerEm 每em单位数
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// 返回: []byte head表数据
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func buildHeadTable(unitsPerEm uint16) []byte {
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buf := new(bytes.Buffer)
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binary.Write(buf, binary.BigEndian, uint16(1))
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binary.Write(buf, binary.BigEndian, uint16(0))
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binary.Write(buf, binary.BigEndian, uint32(0))
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binary.Write(buf, binary.BigEndian, uint32(0))
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binary.Write(buf, binary.BigEndian, uint32(0x5F0F3CF5))
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binary.Write(buf, binary.BigEndian, uint16(0))
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binary.Write(buf, binary.BigEndian, unitsPerEm)
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binary.Write(buf, binary.BigEndian, int64(0))
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binary.Write(buf, binary.BigEndian, int64(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(-500))
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binary.Write(buf, binary.BigEndian, int16(1000))
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binary.Write(buf, binary.BigEndian, int16(1000))
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binary.Write(buf, binary.BigEndian, uint16(0))
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binary.Write(buf, binary.BigEndian, uint16(0))
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binary.Write(buf, binary.BigEndian, int16(2))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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return buf.Bytes()
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}
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// buildHheaTable 构建hhea表
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// 入参: numGlyphs 字形数量
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// 返回: []byte hhea表数据
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func buildHheaTable(numGlyphs uint16) []byte {
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buf := new(bytes.Buffer)
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binary.Write(buf, binary.BigEndian, uint16(1))
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binary.Write(buf, binary.BigEndian, uint16(0))
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binary.Write(buf, binary.BigEndian, int16(800))
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binary.Write(buf, binary.BigEndian, int16(-200))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, uint16(1000))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(1000))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, uint16(numGlyphs))
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return buf.Bytes()
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}
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// buildCFFMaxpTable 构建CFF轮廓使用的maxp 0.5表
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// 入参: numGlyphs 字形数量
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// 返回: []byte maxp表数据
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func buildCFFMaxpTable(numGlyphs uint16) []byte {
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buf := new(bytes.Buffer)
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binary.Write(buf, binary.BigEndian, uint32(0x00005000))
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binary.Write(buf, binary.BigEndian, uint16(numGlyphs))
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return buf.Bytes()
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}
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// buildTrueTypeMaxpTable 构建TrueType轮廓使用的maxp 1.0表
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// 入参: numGlyphs 字形数量
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// 返回: []byte maxp表数据
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func buildTrueTypeMaxpTable(numGlyphs uint16) []byte {
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buf := new(bytes.Buffer)
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binary.Write(buf, binary.BigEndian, uint32(0x00010000))
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binary.Write(buf, binary.BigEndian, uint16(numGlyphs))
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for i := 0; i < 13; i++ {
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binary.Write(buf, binary.BigEndian, uint16(0))
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}
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return buf.Bytes()
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}
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// buildOS2Table 构建OS/2表 (使用默认Metrics)
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// 返回: []byte OS/2表数据
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func buildOS2Table() []byte {
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return buildOS2TableWithMetrics(800, -200)
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}
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// buildOS2TableWithMetrics 构建OS/2表
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// 入参: ascender 上升部, descender 下降部
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// 返回: []byte OS/2表数据
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func buildOS2TableWithMetrics(ascender, descender int16) []byte {
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os2 := new(bytes.Buffer)
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binary.Write(os2, binary.BigEndian, uint16(3))
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binary.Write(os2, binary.BigEndian, int16(500))
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binary.Write(os2, binary.BigEndian, uint16(400))
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binary.Write(os2, binary.BigEndian, uint16(5))
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binary.Write(os2, binary.BigEndian, uint16(0))
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binary.Write(os2, binary.BigEndian, int16(250))
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binary.Write(os2, binary.BigEndian, int16(250))
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binary.Write(os2, binary.BigEndian, int16(0))
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binary.Write(os2, binary.BigEndian, int16(0))
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binary.Write(os2, binary.BigEndian, int16(250))
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binary.Write(os2, binary.BigEndian, int16(250))
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binary.Write(os2, binary.BigEndian, int16(0))
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binary.Write(os2, binary.BigEndian, int16(0))
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binary.Write(os2, binary.BigEndian, int16(50))
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binary.Write(os2, binary.BigEndian, int16(250))
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binary.Write(os2, binary.BigEndian, int16(0))
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os2.Write(make([]byte, 10))
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binary.Write(os2, binary.BigEndian, uint32(0))
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binary.Write(os2, binary.BigEndian, uint32(0))
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binary.Write(os2, binary.BigEndian, uint32(0))
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binary.Write(os2, binary.BigEndian, uint32(0))
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os2.WriteString("PfEd")
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binary.Write(os2, binary.BigEndian, uint16(0x0040))
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binary.Write(os2, binary.BigEndian, uint16(0))
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binary.Write(os2, binary.BigEndian, uint16(255))
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binary.Write(os2, binary.BigEndian, ascender)
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binary.Write(os2, binary.BigEndian, descender)
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binary.Write(os2, binary.BigEndian, int16(0))
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binary.Write(os2, binary.BigEndian, uint16(ascender))
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if descender < 0 {
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binary.Write(os2, binary.BigEndian, uint16(-descender))
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} else {
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binary.Write(os2, binary.BigEndian, uint16(descender))
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}
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binary.Write(os2, binary.BigEndian, uint32(0))
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binary.Write(os2, binary.BigEndian, uint32(0))
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binary.Write(os2, binary.BigEndian, int16(0))
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binary.Write(os2, binary.BigEndian, int16(0))
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binary.Write(os2, binary.BigEndian, uint16(0))
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binary.Write(os2, binary.BigEndian, uint16(0))
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binary.Write(os2, binary.BigEndian, uint16(0))
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return os2.Bytes()
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}
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// buildNameTable 构建name表 (最小化)
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// 返回: []byte name表数据
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func buildNameTable() []byte {
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buf := new(bytes.Buffer)
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binary.Write(buf, binary.BigEndian, uint16(0))
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binary.Write(buf, binary.BigEndian, uint16(0))
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binary.Write(buf, binary.BigEndian, uint16(6))
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return buf.Bytes()
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}
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// buildPostTable 构建post表 (版本3.0, 无字形名称)
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// 返回: []byte post表数据
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func buildPostTable() []byte {
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buf := new(bytes.Buffer)
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binary.Write(buf, binary.BigEndian, uint32(0x00030000))
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binary.Write(buf, binary.BigEndian, uint32(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, int16(0))
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binary.Write(buf, binary.BigEndian, uint32(0))
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binary.Write(buf, binary.BigEndian, uint32(0))
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binary.Write(buf, binary.BigEndian, uint32(0))
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binary.Write(buf, binary.BigEndian, uint32(0))
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binary.Write(buf, binary.BigEndian, uint32(0))
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return buf.Bytes()
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}
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// buildHmtxTable 构建hmtx表
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// 入参: widths 宽度列表
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// 返回: []byte hmtx表数据
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func buildHmtxTable(widths []uint16) []byte {
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buf := new(bytes.Buffer)
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for _, w := range widths {
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binary.Write(buf, binary.BigEndian, uint16(w))
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binary.Write(buf, binary.BigEndian, int16(0))
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}
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return buf.Bytes()
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}
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// serializeOTF 序列化OpenType字体结构
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// 入参: tables 表数据映射
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// 返回: []byte 完整字体数据, error 错误信息
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func serializeOTF(tables map[string][]byte) ([]byte, error) {
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numTables := uint16(len(tables))
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entrySelector := 0
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for 1<<(entrySelector+1) <= int(numTables) {
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entrySelector++
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}
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searchRange := 1 << (entrySelector + 4)
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rangeShift := int(numTables)*16 - searchRange
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buf := new(bytes.Buffer)
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if _, ok := tables["CFF "]; ok {
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buf.WriteString("OTTO")
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} else {
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binary.Write(buf, binary.BigEndian, uint32(0x00010000))
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}
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binary.Write(buf, binary.BigEndian, numTables)
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binary.Write(buf, binary.BigEndian, uint16(searchRange))
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binary.Write(buf, binary.BigEndian, uint16(entrySelector))
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binary.Write(buf, binary.BigEndian, uint16(rangeShift))
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var tags []string
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for t := range tables {
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tags = append(tags, t)
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}
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sort.Strings(tags)
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headerSize := 12 + 16*int(numTables)
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offset := headerSize
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var records []otfTableRecord
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for _, tag := range tags {
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data := tables[tag]
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pad := (4 - (len(data) % 4)) % 4
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padded := make([]byte, len(data)+pad)
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copy(padded, data)
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if tag == "head" && len(data) >= 12 {
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clear(padded[8:12])
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}
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cs := calcTableChecksum(padded)
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records = append(records, otfTableRecord{tag, cs, offset, len(data), padded})
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offset += len(padded)
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}
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for _, r := range records {
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buf.WriteString(r.tag)
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binary.Write(buf, binary.BigEndian, r.checksum)
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binary.Write(buf, binary.BigEndian, uint32(r.offset))
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binary.Write(buf, binary.BigEndian, uint32(r.length))
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}
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for _, r := range records {
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buf.Write(r.data)
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}
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fullData := buf.Bytes()
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for _, r := range records {
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if r.tag == "head" {
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adjOffset := r.offset + 8
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if adjOffset+4 <= len(fullData) {
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binary.BigEndian.PutUint32(fullData[adjOffset:], 0)
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cs := calcTableChecksum(fullData)
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checksumAdj := 0xB1B0AFBA - cs
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binary.BigEndian.PutUint32(fullData[adjOffset:], checksumAdj)
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}
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break
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}
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}
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return fullData, nil
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}
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