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https://github.com/xiaoqidun/ofdgo.git
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feat(字体渲染): 加强内嵌字体渲染成功率
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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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"bytes"
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"encoding/binary"
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"fmt"
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)
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// FixFontData 修复字体数据
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// 本函数主要解决嵌入字体缺失 OS/2 表导致部分渲染库（如 tdewolff/font）Panic 的问题
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// 通过解析 hhea 表获取 Ascender/Descender 等度量信息，构造并注入一个标准的 OS/2 表
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// 入参: data 原始字体文件数据
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// 返回: bool 是否进行了修补, []byte 修复后的字体数据, error 错误信息
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func FixFontData(data []byte) (bool, []byte, error) {
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if len(data) < 12 {
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return false, data, nil
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}
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numTables := binary.BigEndian.Uint16(data[4:6])
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hasOS2 := false
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type TableRecord struct {
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Tag string
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CheckSum uint32
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Offset uint32
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Length uint32
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}
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tables := make([]TableRecord, 0, numTables)
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var hhea TableRecord
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hasHhea := false
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pos := 12
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for i := 0; i < int(numTables); i++ {
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if len(data) < pos+16 {
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return false, data, nil
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}
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tag := string(data[pos : pos+4])
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checkSum := binary.BigEndian.Uint32(data[pos+4 : pos+8])
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offset := binary.BigEndian.Uint32(data[pos+8 : pos+12])
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length := binary.BigEndian.Uint32(data[pos+12 : pos+16])
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tables = append(tables, TableRecord{tag, checkSum, offset, length})
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if tag == "OS/2" {
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hasOS2 = true
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}
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if tag == "hhea" {
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hhea = TableRecord{tag, checkSum, offset, length}
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hasHhea = true
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}
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pos += 16
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}
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if hasOS2 {
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return false, data, nil
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}
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if !hasHhea {
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return false, data, nil
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}
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if uint32(len(data)) < hhea.Offset+hhea.Length {
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return false, data, nil
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}
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hheaData := data[hhea.Offset : hhea.Offset+hhea.Length]
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if len(hheaData) < 10 {
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return false, data, nil
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}
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ascender := int16(binary.BigEndian.Uint16(hheaData[4:6]))
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descender := int16(binary.BigEndian.Uint16(hheaData[6:8]))
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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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for i := 0; i < 11; i++ {
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binary.Write(os2, binary.BigEndian, int16(0))
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}
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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(0x0020))
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binary.Write(os2, binary.BigEndian, uint16(0xFFFD))
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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(1))
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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(0x0020))
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binary.Write(os2, binary.BigEndian, uint16(0))
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os2Data := os2.Bytes()
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os2CheckSum := calcTableChecksum(os2Data)
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newNumTables := numTables + 1
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entrySelector := 0
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for 1<<(entrySelector+1) <= int(newNumTables) {
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entrySelector++
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}
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searchRange := 1 << (entrySelector + 4)
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rangeShift := int(newNumTables)*16 - searchRange
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buf := new(bytes.Buffer)
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buf.Write(data[0:4])
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binary.Write(buf, binary.BigEndian, uint16(newNumTables))
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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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newTables := append(tables, TableRecord{
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Tag: "OS/2",
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CheckSum: os2CheckSum,
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Offset: 0,
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Length: uint32(len(os2Data)),
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})
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for i := 0; i < len(newTables); i++ {
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for j := i + 1; j < len(newTables); j++ {
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if newTables[i].Tag > newTables[j].Tag {
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newTables[i], newTables[j] = newTables[j], newTables[i]
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}
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}
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}
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headerSize := 12 + 16*uint32(len(newTables))
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currentOffset := headerSize
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for i := range newTables {
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t := &newTables[i]
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t.Offset = currentOffset
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currentOffset += align4(t.Length)
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}
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for _, t := range newTables {
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buf.WriteString(t.Tag)
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binary.Write(buf, binary.BigEndian, t.CheckSum)
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binary.Write(buf, binary.BigEndian, t.Offset)
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binary.Write(buf, binary.BigEndian, t.Length)
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}
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for _, t := range newTables {
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var tableData []byte
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if t.Tag == "OS/2" {
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tableData = os2Data
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} else {
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found := false
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for _, old := range tables {
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if old.Tag == t.Tag {
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if uint32(len(data)) < old.Offset+old.Length {
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return false, data, nil
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}
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tableData = data[old.Offset : old.Offset+old.Length]
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found = true
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break
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}
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}
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if !found {
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return false, data, fmt.Errorf("lost table %s", t.Tag)
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}
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}
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buf.Write(tableData)
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padding := align4(t.Length) - t.Length
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for k := uint32(0); k < padding; k++ {
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buf.WriteByte(0)
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}
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}
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fullData := buf.Bytes()
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var newHeadOffset uint32
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var newHeadLength uint32
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for _, t := range newTables {
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if t.Tag == "head" {
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newHeadOffset = t.Offset
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newHeadLength = t.Length
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}
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}
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if newHeadLength >= 12 {
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checkSumAdjPos := newHeadOffset + 8
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binary.BigEndian.PutUint32(fullData[checkSumAdjPos:checkSumAdjPos+4], 0)
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cs := calcTableChecksum(fullData)
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adjustment := 0xB1B0AFBA - cs
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binary.BigEndian.PutUint32(fullData[checkSumAdjPos:checkSumAdjPos+4], adjustment)
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}
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return true, fullData, nil
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}
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// align4 计算 4 字节对齐后的长度
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// 入参: n 原始长度
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// 返回: uint32 对齐后的长度
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func align4(n uint32) uint32 {
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return (n + 3) & ^uint32(3)
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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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+9
-6
@@ -542,7 +542,10 @@ func (r *Renderer) loadFont(fontID string) *canvas.FontFamily {
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ff := canvas.NewFontFamily(of.FontName)
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if of.FontFile != "" {
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if fontData, err := r.Reader.ResData(of.FontFile); err == nil {
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fontStyle := canvas.FontRegular
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if _, fixedData, err := FixFontData(fontData); err == nil {
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fontData = fixedData
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}
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var fontStyle canvas.FontStyle
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if of.Bold {
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fontStyle |= canvas.FontBold
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}
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@@ -590,15 +593,15 @@ func (r *Renderer) loadFont(fontID string) *canvas.FontFamily {
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names := []string{of.FamilyName, of.FontName}
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aliases := map[string]string{
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"simhei": "SimHei",
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"黑体": "SimHei",
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"黑体": "SimHei",
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"microsoft yahei": "Microsoft YaHei",
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"微软雅黑": "Microsoft YaHei",
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"微软雅黑": "Microsoft YaHei",
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"simsun": "SimSun",
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"宋体": "SimSun",
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"宋体": "SimSun",
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"kaiti": "KaiTi",
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"楷体": "KaiTi",
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"楷体": "KaiTi",
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"fangsong": "FangSong",
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"仿宋": "FangSong",
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"仿宋": "FangSong",
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"arial": "Arial",
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"segoe ui": "Segoe UI",
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"times new roman": "Times New Roman",
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