feat(字体渲染): 加强内嵌字体渲染成功率

ofdgo_font.go

@@ -0,0 +1,223 @@
+// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ofdgo
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+)
+
+// FixFontData 修复字体数据
+// 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
+// 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
+// 入参: data 原始字体文件数据
+// 返回: bool 是否进行了修补, []byte 修复后的字体数据, error 错误信息
+func FixFontData(data []byte) (bool, []byte, error) {
+	if len(data) < 12 {
+		return false, data, nil
+	}
+	numTables := binary.BigEndian.Uint16(data[4:6])
+	hasOS2 := false
+	type TableRecord struct {
+		Tag      string
+		CheckSum uint32
+		Offset   uint32
+		Length   uint32
+	}
+	tables := make([]TableRecord, 0, numTables)
+	var hhea TableRecord
+	hasHhea := false
+	pos := 12
+	for i := 0; i < int(numTables); i++ {
+		if len(data) < pos+16 {
+			return false, data, nil
+		}
+		tag := string(data[pos : pos+4])
+		checkSum := binary.BigEndian.Uint32(data[pos+4 : pos+8])
+		offset := binary.BigEndian.Uint32(data[pos+8 : pos+12])
+		length := binary.BigEndian.Uint32(data[pos+12 : pos+16])
+		tables = append(tables, TableRecord{tag, checkSum, offset, length})
+		if tag == "OS/2" {
+			hasOS2 = true
+		}
+		if tag == "hhea" {
+			hhea = TableRecord{tag, checkSum, offset, length}
+			hasHhea = true
+		}
+		pos += 16
+	}
+	if hasOS2 {
+		return false, data, nil
+	}
+	if !hasHhea {
+		return false, data, nil
+	}
+	if uint32(len(data)) < hhea.Offset+hhea.Length {
+		return false, data, nil
+	}
+	hheaData := data[hhea.Offset : hhea.Offset+hhea.Length]
+	if len(hheaData) < 10 {
+		return false, data, nil
+	}
+	ascender := int16(binary.BigEndian.Uint16(hheaData[4:6]))
+	descender := int16(binary.BigEndian.Uint16(hheaData[6:8]))
+	os2 := new(bytes.Buffer)
+	binary.Write(os2, binary.BigEndian, uint16(3))
+	binary.Write(os2, binary.BigEndian, int16(500))
+	binary.Write(os2, binary.BigEndian, uint16(400))
+	binary.Write(os2, binary.BigEndian, uint16(5))
+	binary.Write(os2, binary.BigEndian, uint16(0))
+	for i := 0; i < 11; i++ {
+		binary.Write(os2, binary.BigEndian, int16(0))
+	}
+	os2.Write(make([]byte, 10))
+	binary.Write(os2, binary.BigEndian, uint32(0))
+	binary.Write(os2, binary.BigEndian, uint32(0))
+	binary.Write(os2, binary.BigEndian, uint32(0))
+	binary.Write(os2, binary.BigEndian, uint32(0))
+	os2.WriteString("PfEd")
+	binary.Write(os2, binary.BigEndian, uint16(0x0040))
+	binary.Write(os2, binary.BigEndian, uint16(0x0020))
+	binary.Write(os2, binary.BigEndian, uint16(0xFFFD))
+	binary.Write(os2, binary.BigEndian, ascender)
+	binary.Write(os2, binary.BigEndian, descender)
+	binary.Write(os2, binary.BigEndian, int16(0))
+	binary.Write(os2, binary.BigEndian, uint16(ascender))
+	if descender < 0 {
+		binary.Write(os2, binary.BigEndian, uint16(-descender))
+	} else {
+		binary.Write(os2, binary.BigEndian, uint16(descender))
+	}
+	binary.Write(os2, binary.BigEndian, uint32(1))
+	binary.Write(os2, binary.BigEndian, uint32(0))
+	binary.Write(os2, binary.BigEndian, int16(0))
+	binary.Write(os2, binary.BigEndian, int16(0))
+	binary.Write(os2, binary.BigEndian, uint16(0))
+	binary.Write(os2, binary.BigEndian, uint16(0x0020))
+	binary.Write(os2, binary.BigEndian, uint16(0))
+	os2Data := os2.Bytes()
+	os2CheckSum := calcTableChecksum(os2Data)
+	newNumTables := numTables + 1
+	entrySelector := 0
+	for 1<<(entrySelector+1) <= int(newNumTables) {
+		entrySelector++
+	}
+	searchRange := 1 << (entrySelector + 4)
+	rangeShift := int(newNumTables)*16 - searchRange
+	buf := new(bytes.Buffer)
+	buf.Write(data[0:4])
+	binary.Write(buf, binary.BigEndian, uint16(newNumTables))
+	binary.Write(buf, binary.BigEndian, uint16(searchRange))
+	binary.Write(buf, binary.BigEndian, uint16(entrySelector))
+	binary.Write(buf, binary.BigEndian, uint16(rangeShift))
+	newTables := append(tables, TableRecord{
+		Tag:      "OS/2",
+		CheckSum: os2CheckSum,
+		Offset:   0,
+		Length:   uint32(len(os2Data)),
+	})
+	for i := 0; i < len(newTables); i++ {
+		for j := i + 1; j < len(newTables); j++ {
+			if newTables[i].Tag > newTables[j].Tag {
+				newTables[i], newTables[j] = newTables[j], newTables[i]
+			}
+		}
+	}
+	headerSize := 12 + 16*uint32(len(newTables))
+	currentOffset := headerSize
+	for i := range newTables {
+		t := &newTables[i]
+		t.Offset = currentOffset
+		currentOffset += align4(t.Length)
+	}
+	for _, t := range newTables {
+		buf.WriteString(t.Tag)
+		binary.Write(buf, binary.BigEndian, t.CheckSum)
+		binary.Write(buf, binary.BigEndian, t.Offset)
+		binary.Write(buf, binary.BigEndian, t.Length)
+	}
+	for _, t := range newTables {
+		var tableData []byte
+		if t.Tag == "OS/2" {
+			tableData = os2Data
+		} else {
+			found := false
+			for _, old := range tables {
+				if old.Tag == t.Tag {
+					if uint32(len(data)) < old.Offset+old.Length {
+						return false, data, nil
+					}
+					tableData = data[old.Offset : old.Offset+old.Length]
+					found = true
+					break
+				}
+			}
+			if !found {
+				return false, data, fmt.Errorf("lost table %s", t.Tag)
+			}
+		}
+		buf.Write(tableData)
+		padding := align4(t.Length) - t.Length
+		for k := uint32(0); k < padding; k++ {
+			buf.WriteByte(0)
+		}
+	}
+	fullData := buf.Bytes()
+	var newHeadOffset uint32
+	var newHeadLength uint32
+	for _, t := range newTables {
+		if t.Tag == "head" {
+			newHeadOffset = t.Offset
+			newHeadLength = t.Length
+		}
+	}
+	if newHeadLength >= 12 {
+		checkSumAdjPos := newHeadOffset + 8
+		binary.BigEndian.PutUint32(fullData[checkSumAdjPos:checkSumAdjPos+4], 0)
+		cs := calcTableChecksum(fullData)
+		adjustment := 0xB1B0AFBA - cs
+		binary.BigEndian.PutUint32(fullData[checkSumAdjPos:checkSumAdjPos+4], adjustment)
+	}
+	return true, fullData, nil
+}
+
+// align4 计算 4 字节对齐后的长度
+// 入参: n 原始长度
+// 返回: uint32 对齐后的长度
+func align4(n uint32) uint32 {
+	return (n + 3) & ^uint32(3)
+}
+
+// calcTableChecksum 计算字体表校验和
+// 入参: data 表数据
+// 返回: uint32 校验和
+func calcTableChecksum(data []byte) uint32 {
+	var sum uint32
+	length := len(data)
+	for i := 0; i < length; i += 4 {
+		if i+4 <= length {
+			sum += binary.BigEndian.Uint32(data[i : i+4])
+		} else {
+			var val uint32
+			rem := data[i:]
+			for j, b := range rem {
+				val |= uint32(b) << (24 - 8*j)
+			}
+			sum += val
+		}
+	}
+	return sum
+}

ofdgo_renderer.go

@@ -542,7 +542,10 @@ func (r *Renderer) loadFont(fontID string) *canvas.FontFamily {
 	ff := canvas.NewFontFamily(of.FontName)
 	if of.FontFile != "" {
 		if fontData, err := r.Reader.ResData(of.FontFile); err == nil {
-			fontStyle := canvas.FontRegular
+			if _, fixedData, err := FixFontData(fontData); err == nil {
+				fontData = fixedData
+			}
+			var fontStyle canvas.FontStyle
 			if of.Bold {
 				fontStyle |= canvas.FontBold
 			}
@@ -590,15 +593,15 @@ func (r *Renderer) loadFont(fontID string) *canvas.FontFamily {
 	names := []string{of.FamilyName, of.FontName}
 	aliases := map[string]string{
 		"simhei":          "SimHei",
-		"黑体":              "SimHei",
+		"黑体":            "SimHei",
 		"microsoft yahei": "Microsoft YaHei",
-		"微软雅黑":            "Microsoft YaHei",
+		"微软雅黑":        "Microsoft YaHei",
 		"simsun":          "SimSun",
-		"宋体":              "SimSun",
+		"宋体":            "SimSun",
 		"kaiti":           "KaiTi",
-		"楷体":              "KaiTi",
+		"楷体":            "KaiTi",
 		"fangsong":        "FangSong",
-		"仿宋":              "FangSong",
+		"仿宋":            "FangSong",
 		"arial":           "Arial",
 		"segoe ui":        "Segoe UI",
 		"times new roman": "Times New Roman",