feat(归并文件): 归并根包文件，保持接口不变

ofdgo_font_metrics.go

@@ -15,6 +15,7 @@
 package ofdgo
 
 import (
+	"encoding/binary"
 	"fmt"
 	"sync"
 
@@ -24,6 +25,34 @@ import (
 // sfntGlyphBoundsLimit 限制单个字体保留的字形与字号边界数量
 const sfntGlyphBoundsLimit = 4096
 
+// 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
+	Data      []byte
+	Font      Font
+	Extension string
+	CanSubset bool
+}
+
+// FontUsage 描述全包已确认的字体引用，Unsafe禁止裁剪
+type FontUsage struct {
+	Characters []rune
+	Glyphs     []uint16
+	Unsafe     bool
+}
+
+// FontResourceBackend 解析和裁剪保存资源，独立于显示字体后端
+// SubsetFont的preserve为true时不得改变字形编号，SubsetSourceFont无安全收益时返回nil
+type FontResourceBackend interface {
+	Backend
+	OpenFontResource(file FontFile, index int) (*FontResource, error)
+	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{}
+
 // sfntFontMetrics 保留默认字体度量，写出时不更新原始时间
 type sfntFontMetrics struct {
 	*basefont.SFNT
@@ -47,6 +76,9 @@ type sfntGlyphSize struct {
 // glyphGeometry 将字体轮廓转换为纵轴向下的几何路径
 type glyphGeometry struct{ path GeometryPath }
 
+// sfntResourceMetrics 隔离资源解析器的度量实现
+type sfntResourceMetrics struct{ *basefont.SFNT }
+
 // MoveTo 开始子路径
 // 入参: x 横坐标, y 纵坐标
 func (p *glyphGeometry) MoveTo(x, y float64) {
@@ -180,3 +212,64 @@ func (f sfntFontMetrics) GlyphOutlines(glyphs []uint16, size float64) ([]Geometr
 	}
 	return result, nil
 }
+
+// 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() }