feat(文件合并): 合并字体适配文件

ofdgo_font_resource.go

@@ -14,6 +14,13 @@
 
 package ofdgo
 
+import (
+	"encoding/binary"
+	"fmt"
+
+	basefont "github.com/xiaoqidun/ofdgo/internal/base/font"
+)
+
 // FontResource 保存独立字体数据、标准元信息与只读度量，不包含绘图库类型
 type FontResource struct {
 	FontMetrics
@@ -38,3 +45,70 @@ type FontResourceBackend interface {
 	SubsetFont(data []byte, glyphs []uint16, preserve bool) ([]byte, error)
 	SubsetSourceFont(data []byte, usage FontUsage) ([]byte, error)
 }
+
+// SFNTBackend 提供独立的OpenType字体度量、轮廓和资源处理
+type SFNTBackend struct{}
+
+// sfntResourceMetrics 隔离资源解析器的度量实现
+type sfntResourceMetrics struct{ *basefont.SFNT }
+
+// Name 返回资源后端标识
+// 返回: string 后端标识
+func (SFNTBackend) Name() string { return "sfnt" }
+
+// OpenFontResource 提取独立字体并读取名称、样式和裁剪能力
+// CFF2使用默认实例的静态轮廓，不改变原字体文件
+// 入参: file 字体文件, index 集合索引
+// 返回: *FontResource 字体资源, error 解析错误
+func (SFNTBackend) OpenFontResource(file FontFile, index int) (*FontResource, error) {
+	data, err := file.Face(index)
+	if err != nil {
+		return nil, err
+	}
+	data, err = basefont.DefaultCFF2Font(data)
+	if err != nil {
+		return nil, err
+	}
+	sfnt, err := basefont.ParseSFNT(data)
+	if err != nil {
+		return nil, err
+	}
+	name := basefont.SFNTName(sfnt, 6, 4, 1)
+	if name == "" {
+		return nil, fmt.Errorf("font has no name")
+	}
+	extension := ".ttf"
+	if sfnt.IsCFF {
+		extension = ".otf"
+	}
+	return &FontResource{
+		FontMetrics: sfntResourceMetrics{sfnt}, Data: data, Extension: extension,
+		Font:      Font{FontName: name, FamilyName: basefont.SFNTName(sfnt, 16, 1), Charset: "unicode", Bold: binary.BigEndian.Uint16(sfnt.Tables["head"][44:])&1 != 0, Italic: binary.BigEndian.Uint16(sfnt.Tables["head"][44:])&2 != 0, FixedWidth: len(sfnt.Tables["post"]) >= 16 && binary.BigEndian.Uint32(sfnt.Tables["post"][12:]) != 0},
+		CanSubset: basefont.Subsettable(sfnt),
+	}, nil
+}
+
+// SubsetFont 裁剪新建字体并按要求保留显式字形编号
+// 入参: data 字体数据, glyphs 用字, preserve 是否保留编号
+// 返回: []byte 子集, error 裁剪错误
+func (SFNTBackend) SubsetFont(data []byte, glyphs []uint16, preserve bool) ([]byte, error) {
+	return basefont.SubsetSFNT(data, glyphs, preserve)
+}
+
+// SubsetSourceFont 按全包引用裁剪原字体，不确定时保留原资源
+// 入参: data 字体数据, usage 用字信息
+// 返回: []byte 子集, error 裁剪错误
+func (SFNTBackend) SubsetSourceFont(data []byte, usage FontUsage) ([]byte, error) {
+	u := &basefont.Usage{Characters: make(map[rune]bool), Glyphs: make(map[uint16]bool), Unsafe: usage.Unsafe}
+	for _, char := range usage.Characters {
+		u.Characters[char] = true
+	}
+	for _, glyph := range usage.Glyphs {
+		u.Glyphs[glyph] = true
+	}
+	return basefont.SubsetSourceSFNT(data, u), nil
+}
+
+// Write 返回未改动元信息的字体数据
+// 返回: []byte 字体数据
+func (f sfntResourceMetrics) Write() []byte { return f.SFNT.Write() }