feat(编辑能力): 修复字体选择与裁剪边界问题

ofdgo_font_file.go

@@ -0,0 +1,112 @@
+// 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"
+	"strings"
+
+	"github.com/tdewolff/font"
+)
+
+// FontFace 字体文件中的字体名称与零起始索引，不依赖文件名
+type FontFace struct {
+	Index          int      `json:"index"`
+	FullName       string   `json:"fullName"`
+	Family         string   `json:"family"`
+	Style          string   `json:"style"`
+	PostScriptName string   `json:"postscriptName"`
+	Names          []string `json:"names"`
+}
+
+// Faces 读取字体名称表，集合文件按原顺序列出各项，不解析字形轮廓
+// 返回: []FontFace 字体列表, error 格式或名称表错误
+func (f FontFile) Faces() ([]FontFace, error) {
+	data, err := font.ToSFNT(f.Data)
+	if err != nil {
+		return nil, err
+	}
+	count, err := fontFileCount(data)
+	if err != nil {
+		return nil, err
+	}
+	faces := make([]FontFace, 0, count)
+	for index := 0; index < count; index++ {
+		tables, err := fontFileTables(data, index)
+		if err != nil {
+			return nil, err
+		}
+		records, values := fontNameValues(tables["name"])
+		name := func(ids ...uint16) string {
+			for _, id := range ids {
+				for _, record := range records {
+					if record.Name == id {
+						if value := strings.TrimSpace(values[[4]uint16{record.Platform, record.Encoding, record.Language, id}]); value != "" {
+							return value
+						}
+					}
+				}
+			}
+			return ""
+		}
+		face := FontFace{Index: index, FullName: name(4, 6, 16, 1), Family: name(16, 1), Style: name(17, 2), PostScriptName: name(6), Names: fontNamesFromTable(tables["name"])}
+		if face.FullName == "" {
+			return nil, fmt.Errorf("font %d has no usable name", index)
+		}
+		faces = append(faces, face)
+	}
+	return faces, nil
+}
+
+// Face 提取指定字体，返回独立的OpenType数据，可用于预览或AddFont，且不修改原文件
+// 入参: index 零起始字体索引，非集合文件只能为0
+// 返回: []byte 独立字体数据, error 格式或索引错误
+func (f FontFile) Face(index int) ([]byte, error) {
+	data, err := font.ToSFNT(f.Data)
+	if err != nil {
+		return nil, err
+	}
+	if bytes.HasPrefix(data, []byte("ttcf")) {
+		return extractCollectionFont(data, index)
+	}
+	if _, err := fontFileTables(data, index); err != nil {
+		return nil, err
+	}
+	return bytes.Clone(data), nil
+}
+
+// fontFileCount 校验字体或集合头并读取字体数量
+// 入参: data OpenType数据
+// 返回: int 字体数量, error 格式错误
+func fontFileCount(data []byte) (int, error) {
+	if len(data) < 12 {
+		return 0, fmt.Errorf("invalid font header")
+	}
+	switch string(data[:4]) {
+	case "\x00\x01\x00\x00", "OTTO", "true":
+		return 1, nil
+	case "ttcf":
+		version := binary.BigEndian.Uint32(data[4:])
+		count := uint64(binary.BigEndian.Uint32(data[8:]))
+		if (version != 0x00010000 && version != 0x00020000) || count == 0 || count > uint64(len(data)-12)/4 {
+			return 0, fmt.Errorf("invalid font collection header")
+		}
+		return int(count), nil
+	default:
+		return 0, fmt.Errorf("invalid OpenType header")
+	}
+}