feat(渲染能力): 优化字体名称识别，修复字体误回退

ofdgo_font_name.go

@@ -0,0 +1,160 @@
+// 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"
+	"io"
+	"unicode/utf16"
+
+	"golang.org/x/text/encoding/charmap"
+)
+
+// fontNameRecord 字体名称表记录
+type fontNameRecord struct {
+	Platform uint16
+	Encoding uint16
+	Language uint16
+	Name     uint16
+	Length   uint16
+	Offset   uint16
+}
+
+// appendFontFileNames 追加字体内部名称对应的候选
+// 入参: candidates 字体候选, file 字体文件, names 字体内部名称
+// 返回: []fontFileCandidate 字体候选列表
+func appendFontFileNames(candidates []fontFileCandidate, file fontFileCandidate, names []string) []fontFileCandidate {
+	base := file.normalized
+	for _, name := range names {
+		file.normalized = fontNormalizeName(name)
+		if file.normalized != base {
+			candidates = append(candidates, file)
+		}
+	}
+	return candidates
+}
+
+// fontFileNames 读取字体或集合首项的名称
+// 入参: file 字体数据
+// 返回: []string 字体名称及带样式的字体族名称
+func fontFileNames(file io.ReaderAt) []string {
+	var header [12]byte
+	if _, err := file.ReadAt(header[:], 0); err != nil {
+		return nil
+	}
+	var offset int64
+	if string(header[:4]) == "ttcf" {
+		if binary.BigEndian.Uint32(header[8:]) == 0 {
+			return nil
+		}
+		var entry [4]byte
+		if _, err := file.ReadAt(entry[:], 12); err != nil {
+			return nil
+		}
+		offset = int64(binary.BigEndian.Uint32(entry[:]))
+		if _, err := file.ReadAt(header[:], offset); err != nil {
+			return nil
+		}
+	}
+	switch string(header[:4]) {
+	case "\x00\x01\x00\x00", "OTTO", "true":
+	default:
+		return nil
+	}
+	entries := make([]byte, int(binary.BigEndian.Uint16(header[4:]))*16)
+	if _, err := file.ReadAt(entries, offset+12); err != nil {
+		return nil
+	}
+	for i := 0; i < len(entries); i += 16 {
+		if string(entries[i:i+4]) != "name" {
+			continue
+		}
+		offset := int64(binary.BigEndian.Uint32(entries[i+8:]))
+		length := int64(binary.BigEndian.Uint32(entries[i+12:]))
+		data, err := io.ReadAll(io.NewSectionReader(file, offset, length))
+		if err != nil {
+			return nil
+		}
+		return fontNamesFromTable(data)
+	}
+	return nil
+}
+
+// fontNamesFromTable 解析字体名称表
+// 入参: data 名称表数据
+// 返回: []string 字体名称列表
+func fontNamesFromTable(data []byte) []string {
+	if len(data) < 6 || binary.BigEndian.Uint16(data) > 1 {
+		return nil
+	}
+	count := int(binary.BigEndian.Uint16(data[2:]))
+	storage := int(binary.BigEndian.Uint16(data[4:]))
+	if 6+count*12 > storage || storage > len(data) {
+		return nil
+	}
+	records := make([]fontNameRecord, count)
+	if err := binary.Read(bytes.NewReader(data[6:]), binary.BigEndian, records); err != nil {
+		return nil
+	}
+	values := make(map[[4]uint16]string)
+	for _, record := range records {
+		switch record.Name {
+		case 1, 2, 4, 6, 16, 17:
+		default:
+			continue
+		}
+		start := storage + int(record.Offset)
+		end := start + int(record.Length)
+		if end > len(data) {
+			continue
+		}
+		var name string
+		switch {
+		case record.Platform == 0 || record.Platform == 3 && (record.Encoding == 0 || record.Encoding == 1 || record.Encoding == 10):
+			if record.Length%2 != 0 {
+				continue
+			}
+			chars := make([]uint16, int(record.Length)/2)
+			for i := range chars {
+				chars[i] = binary.BigEndian.Uint16(data[start+i*2:])
+			}
+			name = string(utf16.Decode(chars))
+		case record.Platform == 1 && record.Encoding == 0:
+			name, _ = charmap.Macintosh.NewDecoder().String(string(data[start:end]))
+		default:
+			continue
+		}
+		values[[4]uint16{record.Platform, record.Encoding, record.Language, record.Name}] = name
+	}
+	var names []string
+	seen := make(map[string]bool)
+	for _, record := range records {
+		key := [4]uint16{record.Platform, record.Encoding, record.Language, record.Name}
+		name := values[key]
+		switch record.Name {
+		case 1, 16:
+			key[3]++
+			if style := values[key]; style != "" && name != "" {
+				name += " " + style
+			}
+		case 4, 6:
+		default:
+			continue
+		}
+		names = appendFontName(names, seen, name)
+	}
+	return names
+}