feat(字体图像): 优化字体图像性能

internal/base/font/sfnt.go

@@ -18,7 +18,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"maps"
-	"sort"
+	"slices"
 	"sync"
 
 	"github.com/go-text/typesetting/font/opentype/tables"
@@ -34,10 +34,11 @@ type SFNT struct {
 	reverse                            map[uint16][]rune
 }
 
-// sfntCmap 保存编码记录及对应字符映射
+// sfntCmap 保存编码记录及对应字符映射，标记已解析的共享子表
 type sfntCmap struct {
 	platform, encoding, format uint16
 	mapping                    map[rune]uint16
+	duplicate                  bool
 }
 
 // ParseSFNT 校验独立字体的必需表、度量范围及字符映射
@@ -86,6 +87,9 @@ func ParseSFNTTables(table map[string][]byte) (*SFNT, error) {
 	}
 	f.cmaps = cmaps
 	for _, cmap := range f.cmaps {
+		if cmap.duplicate {
+			continue
+		}
 		for _, glyph := range cmap.mapping {
 			if glyph >= f.count {
 				return nil, fmt.Errorf("cmap glyph index out of range")
@@ -150,7 +154,7 @@ func readSFNTCmaps(data []byte) ([]sfntCmap, error) {
 			}
 			parsed[offset] = mapping
 		}
-		result = append(result, sfntCmap{binary.BigEndian.Uint16(record), binary.BigEndian.Uint16(record[2:]), format, mapping})
+		result = append(result, sfntCmap{platform: binary.BigEndian.Uint16(record), encoding: binary.BigEndian.Uint16(record[2:]), format: format, mapping: mapping, duplicate: found})
 	}
 	return result, nil
 }
@@ -164,11 +168,11 @@ func (f *SFNT) UnitsPerEm() uint16 { return f.units }
 func (f *SFNT) NumGlyphs() uint16 { return f.count }
 
 // CmapEntries 返回各编码记录的映射项总数，共享子表按记录分别计数
-// 返回: int 用于缓存预算的映射项数量
-func (f *SFNT) CmapEntries() int {
-	count := 0
+// 返回: uint64 用于缓存预算的映射项数量
+func (f *SFNT) CmapEntries() uint64 {
+	var count uint64
 	for _, cmap := range f.cmaps {
-		count += len(cmap.mapping)
+		count += uint64(len(cmap.mapping))
 	}
 	return count
 }
@@ -178,6 +182,9 @@ func (f *SFNT) CmapEntries() int {
 // 返回: uint16 字形编号
 func (f *SFNT) GlyphIndex(char rune) uint16 {
 	for _, cmap := range f.cmaps {
+		if cmap.duplicate {
+			continue
+		}
 		if gid := cmap.mapping[char]; gid != 0 {
 			return gid
 		}
@@ -193,6 +200,9 @@ func (f *SFNT) glyphCharacters(gid uint16) []rune {
 		f.reverse = make(map[uint16][]rune)
 		seen := make(map[rune]bool)
 		for _, cmap := range f.cmaps {
+			if cmap.duplicate {
+				continue
+			}
 			for char, glyph := range cmap.mapping {
 				if glyph != 0 && !seen[char] {
 					f.reverse[glyph] = append(f.reverse[glyph], char)
@@ -201,7 +211,7 @@ func (f *SFNT) glyphCharacters(gid uint16) []rune {
 			}
 		}
 		for _, chars := range f.reverse {
-			sort.Slice(chars, func(i, j int) bool { return chars[i] < chars[j] })
+			slices.Sort(chars)
 		}
 	})
 	return f.reverse[gid]

internal/base/font/subset.go

@@ -134,7 +134,8 @@ func SubsetSFNT(data []byte, glyphs []uint16, mapped bool) ([]byte, error) {
 		if err != nil {
 			return nil, err
 		}
-		if subset := SubsetSourceSFNT(fixed, usage); subset != nil {
+		sfnt.Tables = tables
+		if subset := subsetSourceSFNT(sfnt, usage, len(fixed)); subset != nil {
 			return subset, nil
 		}
 		return fixed, nil
@@ -147,7 +148,7 @@ func SubsetSFNT(data []byte, glyphs []uint16, mapped bool) ([]byte, error) {
 // 入参: data 字体数据, usage 全包用字记录
 // 返回: []byte 更小的字体子集，无确定收益时为空
 func SubsetSourceSFNT(data []byte, usage *Usage) []byte {
-	if usage.Unsafe || len(usage.Characters)+len(usage.Glyphs) == 0 || bytes.HasPrefix(data, []byte("ttcf")) {
+	if usage == nil || usage.Unsafe || len(usage.Characters)+len(usage.Glyphs) == 0 || bytes.HasPrefix(data, []byte("ttcf")) {
 		return nil
 	}
 	fontTables, err := FileTables(data, 0)
@@ -162,7 +163,17 @@ func SubsetSourceSFNT(data []byte, usage *Usage) []byte {
 		}
 	}
 	sfnt, err := ParseSFNTTables(fontTables)
-	if err != nil || !sfnt.IsTrueType && !sfnt.IsCFF || fontEmbeddingFlags(sfnt)&0x0100 != 0 {
+	if err != nil {
+		return nil
+	}
+	return subsetSourceSFNT(sfnt, usage, len(data))
+}
+
+// subsetSourceSFNT 复用已校验的字体表裁剪字形，仅返回小于原编码的结果
+// 入参: sfnt 已解析字体, usage 用字记录, size 原编码长度
+// 返回: []byte 更小的字体子集，无确定收益时为空
+func subsetSourceSFNT(sfnt *SFNT, usage *Usage, size int) []byte {
+	if usage == nil || usage.Unsafe || len(usage.Characters)+len(usage.Glyphs) == 0 || !sfnt.IsTrueType && !sfnt.IsCFF || fontEmbeddingFlags(sfnt)&0x0100 != 0 {
 		return nil
 	}
 	var unicodeTables []sfntCmap
@@ -178,6 +189,9 @@ func SubsetSourceSFNT(data []byte, usage *Usage) []byte {
 		return nil
 	}
 	glyphs := maps.Clone(usage.Glyphs)
+	if glyphs == nil {
+		glyphs = make(map[uint16]bool)
+	}
 	glyphs[0] = true
 	mapping := make(map[rune]uint16, len(usage.Characters))
 	for char := range usage.Characters {
@@ -210,7 +224,7 @@ func SubsetSourceSFNT(data []byte, usage *Usage) []byte {
 		tables["cmap"] = buildCmapWithVariations(sfnt.NumGlyphs(), mapping, variations)
 		delete(tables, "DSIG")
 		result, err := SerializeOTF(tables)
-		if err != nil || len(result) >= len(data) {
+		if err != nil || len(result) >= size {
 			return nil
 		}
 		return result
@@ -258,7 +272,7 @@ func SubsetSourceSFNT(data []byte, usage *Usage) []byte {
 	clear(tables["head"][8:12])
 	delete(tables, "DSIG")
 	result, err := SerializeOTF(tables)
-	if err != nil || len(result) >= len(data) {
+	if err != nil || len(result) >= size {
 		return nil
 	}
 	return result