feat(后端架构): 完善后端扩展与字体资源解耦，修复元数据保存和缩略图底边

assets/webui/ofdgo.js

@@ -5714,7 +5714,7 @@ function layoutThumbnails() {
 	}
 	view.offsets = offsets;
 	view.gap = 12;
-	view.total = Math.max(0, offsets.at(-1) - 12);
+	view.total = Math.ceil(offsets.at(-1));
 	for (const [index, button] of view.nodes) {
 		layoutThumbnail(button, state.doc.pages[index]);
 		button.style.height = `${offsets[index + 1] - offsets[index] - 12}px`;

ofdgo_backend.go

@@ -20,6 +20,7 @@ import (
 	"image"
 	"io"
 	"reflect"
+	"sync"
 )
 
 // ErrBackendUnavailable 表示未配置所需后端，不会自动切换其他实现
@@ -105,6 +106,7 @@ type EPSBackend interface {
 // RenderBackends 按职责组合后端，nil表示明确禁用，不隐式回退
 // 实例及其Renderer需串行使用，第三方实现无需引用任何内置绘图库
 type RenderBackends struct {
+	Resources FontResourceBackend
 	Fonts     FontBackend
 	Geometry  GeometryBackend
 	Compiler  PageCompiler
@@ -116,6 +118,7 @@ type RenderBackends struct {
 
 // BackendInfo 描述各项能力实际使用的后端，空标识表示未配置
 type BackendInfo struct {
+	Resources string `json:"resources"`
 	Fonts     string `json:"fonts"`
 	Geometry  string `json:"geometry"`
 	Compiler  string `json:"compiler"`
@@ -125,33 +128,61 @@ type BackendInfo struct {
 	EPS       string `json:"eps"`
 }
 
-// NewRenderBackends 创建内置后端组合，各项能力通过Info报告实际提供者
-// 入参: name 内置后端标识
+// NewRenderBackends 创建已注册后端组合，各项能力通过Info报告实际提供者
+// 入参: name 已注册后端标识
 // 返回: RenderBackends 后端组合, error 未知后端错误
 func NewRenderBackends(name string) (RenderBackends, error) {
-	if name != "canvas" {
+	backendRegistry.RLock()
+	factory := backendRegistry.factories[name]
+	backendRegistry.RUnlock()
+	if factory == nil {
 		return RenderBackends{}, fmt.Errorf("unknown render backend %q", name)
 	}
-	return defaultRenderBackends(), nil
+	return factory(), nil
 }
 
-// RenderBackendInfos 列出内置组合及其实际能力，供原生程序和WASM共用
+// RenderBackendInfos 列出已注册组合及其实际能力，供原生程序和WASM共用
 // 返回: map[string]BackendInfo 后端能力
 func RenderBackendInfos() map[string]BackendInfo {
-	return map[string]BackendInfo{"canvas": defaultRenderBackends().Info()}
+	backendRegistry.RLock()
+	factories := make(map[string]func() RenderBackends, len(backendRegistry.factories))
+	for name, factory := range backendRegistry.factories {
+		factories[name] = factory
+	}
+	backendRegistry.RUnlock()
+	result := make(map[string]BackendInfo, len(factories))
+	for name, factory := range factories {
+		result[name] = factory().Info()
+	}
+	return result
 }
 
-// defaultRenderBackends 创建独立的默认配置
-// 返回: RenderBackends 默认后端组合
-func defaultRenderBackends() RenderBackends {
-	backend := CanvasBackend{}
-	return RenderBackends{Fonts: backend, Geometry: backend, Compiler: backend, Raster: backend, SVG: backend, PDF: backend, EPS: backend}
+// backendRegistry 保存后端工厂，不共享有状态的后端实例
+var backendRegistry = struct {
+	sync.RWMutex
+	factories map[string]func() RenderBackends
+}{factories: make(map[string]func() RenderBackends)}
+
+// RegisterRenderBackend 注册后端组合，工厂应返回独立实例，重复标识不会覆盖已有实现
+// 入参: name 后端标识, factory 后端工厂
+// 返回: error 无效或重复注册错误
+func RegisterRenderBackend(name string, factory func() RenderBackends) error {
+	if name == "" || factory == nil {
+		return fmt.Errorf("backend name and factory are required")
+	}
+	backendRegistry.Lock()
+	defer backendRegistry.Unlock()
+	if _, exists := backendRegistry.factories[name]; exists {
+		return fmt.Errorf("render backend %q already registered", name)
+	}
+	backendRegistry.factories[name] = factory
+	return nil
 }
 
 // Info 返回配置中各能力的提供者，不依赖WebUI推断
 // 返回: BackendInfo 后端能力
 func (b RenderBackends) Info() BackendInfo {
-	return BackendInfo{Fonts: backendName(b.Fonts), Geometry: backendName(b.Geometry), Compiler: backendName(b.Compiler), Raster: backendName(b.Raster), SVG: backendName(b.SVG), PDF: backendName(b.PDF), EPS: backendName(b.EPS)}
+	return BackendInfo{Resources: backendName(b.Resources), Fonts: backendName(b.Fonts), Geometry: backendName(b.Geometry), Compiler: backendName(b.Compiler), Raster: backendName(b.Raster), SVG: backendName(b.SVG), PDF: backendName(b.PDF), EPS: backendName(b.EPS)}
 }
 
 // backendName 获取已配置的后端标识

ofdgo_editor.go

@@ -31,7 +31,6 @@ import (
 	"time"
 	"unicode/utf8"
 
-	"github.com/tdewolff/font"
 	"github.com/xiaoqidun/jbig2"
 )
 
@@ -45,7 +44,7 @@ type Editor struct {
 	Info            DocInfo
 	pages           []PageContent
 	resources       []editorResource
-	fonts           map[string]*font.SFNT
+	fonts           map[string]*FontResource
 	fontFS          []fs.FS
 	fontRenderer    *Renderer
 	fontMetrics     map[string]FontMetrics
@@ -86,6 +85,12 @@ func (e *Editor) SetPageCompiler(compiler PageCompiler) {
 // 入参: backends 后端组合，未配置的能力不会沿用默认实现
 func (e *Editor) SetRenderBackends(backends RenderBackends) {
 	fontsChanged := !sameBackend(e.backends.Fonts, backends.Fonts)
+	if !sameBackend(e.backends.Resources, backends.Resources) {
+		e.fonts = make(map[string]*FontResource)
+		for i := range e.resources {
+			e.resources[i].subset = nil
+		}
+	}
 	e.backends = backends
 	if e.fontRenderer != nil {
 		WithRenderBackends(backends)(e.fontRenderer)
@@ -150,7 +155,7 @@ func NewEditor() *Editor {
 			DocID:        hex.EncodeToString(id[:]),
 			CreationDate: time.Now().Format("2006-01-02"),
 		},
-		fonts:       make(map[string]*font.SFNT),
+		fonts:       make(map[string]*FontResource),
 		images:      make(map[string]image.Point),
 		resourceID:  make(map[editorResourceKey]string),
 		fontMetrics: make(map[string]FontMetrics),
@@ -564,67 +569,36 @@ func (e *Editor) nextID() string {
 // 入参: file 字体文件, index 集合内字体索引，单字体为0
 // 返回: string 字体资源标识, error 错误信息
 func (e *Editor) AddFont(file FontFile, index int) (string, error) {
-	data, err := font.ToSFNT(file.Data)
+	if e.backends.Resources == nil {
+		return "", fmt.Errorf("font resources: %w", ErrBackendUnavailable)
+	}
+	parsed, err := e.backends.Resources.OpenFontResource(file, index)
 	if err != nil {
 		return "", err
 	}
-	key := editorResourceKey{checksum: sha256.Sum256(data), index: index}
+	data := parsed.Data
+	key := editorResourceKey{checksum: sha256.Sum256(data)}
 	if id, ok := e.resourceID[key]; ok {
 		return id, nil
 	}
-	data, err = (FontFile{Data: data}).Face(index)
-	if err != nil {
-		return "", err
-	}
-	sfnt, err := font.ParseSFNT(data, 0)
-	if err != nil {
-		return "", err
-	}
-	name := editorFontName(sfnt, font.NamePostScript, font.NameFull, font.NameFontFamily)
-	if name == "" {
-		return "", fmt.Errorf("font has no name")
-	}
 	if err := e.prepareSourceIDs(); err != nil {
 		return "", err
 	}
 	id := e.nextID()
-	extension := ".ttf"
-	if sfnt.IsCFF {
-		extension = ".otf"
-	}
+	definition := parsed.Font
+	definition.ID = id
 	resource := editorResource{
-		name: e.packageName("Res/Fonts/Font_" + id + extension),
+		name: e.packageName("Res/Fonts/Font_" + id + parsed.Extension),
 		data: data,
-		font: &Font{
-			ID: id, FontName: name,
-			FamilyName: editorFontName(sfnt, font.NamePreferredFamily, font.NameFontFamily),
-			Charset:    "unicode",
-			Bold:       sfnt.Head.MacStyle[0],
-			Italic:     sfnt.Head.MacStyle[1],
-			FixedWidth: sfnt.Post.IsFixedPitch != 0,
-		},
+		font: &definition,
 	}
 	resource.font.FontFile = "/" + resource.name
 	e.resources = append(e.resources, resource)
-	e.fonts[id] = sfnt
+	e.fonts[id] = parsed
 	e.resourceID[key] = id
 	return id, nil
 }
 
-// editorFontName 获取字体中的名称
-// 入参: sfnt 字体, names 名称类型，按顺序查找
-// 返回: string 字体名称
-func editorFontName(sfnt *font.SFNT, names ...font.NameID) string {
-	for _, name := range names {
-		for _, record := range sfnt.Name.Get(name) {
-			if value := record.String(); value != "" {
-				return value
-			}
-		}
-	}
-	return ""
-}
-
 // AddImage 注册PNG或JPEG图片，重复资源复用标识，引用后写入文档
 // 不透明纯黑白PNG仅在无损JBIG2编码更小时转换，其他图片保留原始编码
 // 入参: data 图片数据

ofdgo_editor_font.go

@@ -187,6 +187,9 @@ type editorFontSubset struct {
 // 入参: progress 保存进度回调
 // 返回: map[string][]byte 包内字体子集, error 错误信息
 func (e *Editor) subsetFonts(progress editorProgress) (map[string][]byte, error) {
+	if e.backends.Resources == nil {
+		return nil, nil
+	}
 	used := make(map[string]map[uint16]bool)
 	mapped := make(map[string]bool)
 	for _, resource := range e.resources {
@@ -194,7 +197,15 @@ func (e *Editor) subsetFonts(progress editorProgress) (map[string][]byte, error)
 			continue
 		}
 		sfnt := e.fonts[resource.font.ID]
-		if sfnt.IsTrueType && !slices.ContainsFunc([]string{"fvar", "COLR", "CBDT", "sbix", "SVG "}, func(tag string) bool { return sfnt.Tables[tag] != nil }) {
+		if sfnt == nil {
+			var err error
+			sfnt, err = e.backends.Resources.OpenFontResource(FontFile{Data: resource.data}, 0)
+			if err != nil {
+				return nil, err
+			}
+			e.fonts[resource.font.ID] = sfnt
+		}
+		if sfnt.CanSubset {
 			used[resource.font.ID] = make(map[uint16]bool)
 		}
 	}
@@ -309,7 +320,7 @@ func (e *Editor) subsetFonts(progress editorProgress) (map[string][]byte, error)
 		}
 		slices.Sort(ids)
 		if resource.subset == nil || resource.subset.mapped != mapped[resource.font.ID] || !slices.Equal(resource.subset.glyphs, ids) {
-			data, err := subsetEditorFont(resource.data, ids, mapped[resource.font.ID])
+			data, err := e.backends.Resources.SubsetFont(resource.data, ids, mapped[resource.font.ID])
 			if err != nil {
 				return nil, fmt.Errorf("subset font %s: %w", resource.font.FontName, err)
 			}

ofdgo_editor_package.go

@@ -441,9 +441,6 @@ func (e *Editor) sourceInfoXML() ([]byte, error) {
 		return nil, fmt.Errorf("document has no DocInfo")
 	}
 	before, after := e.source.info, e.Info
-	if !reflect.DeepEqual(before.CustomDatas, after.CustomDatas) {
-		return nil, fmt.Errorf("editing imported custom metadata is not supported")
-	}
 	var values [][2]string
 	for _, field := range [][3]string{
 		{"DocID", before.DocID, after.DocID}, {"Title", before.Title, after.Title}, {"Author", before.Author, after.Author},
@@ -454,7 +451,101 @@ func (e *Editor) sourceInfoXML() ([]byte, error) {
 			values = append(values, [2]string{field[0], field[2]})
 		}
 	}
-	return editorXMLSetText(data, info, values), nil
+	data = editorXMLSetText(data, info, values)
+	if !reflect.DeepEqual(before.CustomDatas, after.CustomDatas) {
+		root, err = parseEditorXML(data)
+		if err != nil {
+			return nil, err
+		}
+		return editorCustomDatas(data, root.child("DocBody").child("DocInfo"), after.CustomDatas)
+	}
+	return data, nil
+}
+
+// editorCustomDatas 更新自定义字段，保留容器扩展与同名字段的未知属性和子节点
+// 入参: data 原XML, info 文档信息节点, values 新字段
+// 返回: []byte 修改后的XML, error 编码错误
+func editorCustomDatas(data []byte, info *editorXML, values *CustomDatas) ([]byte, error) {
+	container := info.child("CustomDatas")
+	var items []CustomData
+	if values != nil {
+		items = values.CustomData
+	}
+	byName := make(map[string][]*editorXML)
+	var nodes []*editorXML
+	if container != nil {
+		for _, node := range container.children {
+			if node.name.Local == "CustomData" && (node.name.Space == ofdNamespace || node.name.Space == container.name.Space) {
+				nodes = append(nodes, node)
+				byName[node.attr("Name")] = append(byName[node.attr("Name")], node)
+			}
+		}
+	}
+	var encoded [][]byte
+	for _, item := range items {
+		matches := byName[item.Name]
+		if len(matches) == 0 {
+			entry, err := xml.Marshal(struct {
+				XMLName xml.Name
+				CustomData
+			}{xml.Name{Space: ofdNamespace, Local: "CustomData"}, item})
+			if err != nil {
+				return nil, err
+			}
+			encoded = append(encoded, entry)
+			continue
+		}
+		node := matches[0]
+		byName[item.Name] = matches[1:]
+		var original CustomData
+		if err := xml.Unmarshal(data[node.start:node.end], &original); err != nil {
+			return nil, err
+		}
+		if original.Value == item.Value {
+			encoded = append(encoded, data[node.start:node.end])
+			continue
+		}
+		var content bytes.Buffer
+		if err := xml.EscapeText(&content, []byte(item.Value)); err != nil {
+			return nil, err
+		}
+		for _, child := range node.children {
+			content.Write(data[child.start:child.end])
+		}
+		patch := editorXMLContent(data, node, content.Bytes())
+		entry := append(bytes.Clone(data[node.start:patch.start]), patch.data...)
+		entry = append(entry, data[patch.end:node.end]...)
+		encoded = append(encoded, entry)
+	}
+	if container == nil {
+		if len(encoded) == 0 {
+			return data, nil
+		}
+		content := []byte("<ofd:CustomDatas xmlns:ofd=\"" + ofdNamespace + "\">")
+		content = append(content, bytes.Join(encoded, nil)...)
+		content = append(content, []byte("</ofd:CustomDatas>")...)
+		if info.open == info.end {
+			return editorPatchXML(data, []editorXMLPatch{editorXMLContent(data, info, content)}), nil
+		}
+		return editorPatchXML(data, []editorXMLPatch{{info.close, info.close, content}}), nil
+	}
+	var patches []editorXMLPatch
+	for i, node := range nodes {
+		var entry []byte
+		if i < len(encoded) {
+			entry = encoded[i]
+		}
+		patches = append(patches, editorXMLPatch{node.start, node.end, entry})
+	}
+	if len(encoded) > len(nodes) {
+		added := bytes.Join(encoded[len(nodes):], nil)
+		if container.open == container.end {
+			patches = append(patches, editorXMLContent(data, container, added))
+		} else {
+			patches = append(patches, editorXMLPatch{container.close, container.close, added})
+		}
+	}
+	return editorPatchXML(data, patches), nil
 }
 
 // writeSource 将未修改ZIP条目直接复制到新包，逐项写入改动，不持有原资源解压副本

ofdgo_editor_resources.go

@@ -18,6 +18,7 @@ import (
 	"bufio"
 	"bytes"
 	"encoding/xml"
+	"fmt"
 	"io"
 	"maps"
 	"path"
@@ -172,14 +173,18 @@ func (e *Editor) compactSourceResources(parts map[string][]byte, progress editor
 		}
 		key := strings.ToLower(cleanPackagePath(name))
 		usage := fontFiles[key]
-		if usage == nil || usage.unsafe || refs.files[key] || removed[key] || parts[name] != nil {
+		if e.backends.Resources == nil || usage == nil || usage.unsafe || refs.files[key] || removed[key] || parts[name] != nil {
 			continue
 		}
 		data, err := reader.readFile(name)
 		if err != nil {
 			return nil, err
 		}
-		if subset := subsetSourceFont(data, usage); subset != nil {
+		subset, err := e.backends.Resources.SubsetSourceFont(data, FontUsage{Characters: slices.Sorted(maps.Keys(usage.chars)), Glyphs: slices.Sorted(maps.Keys(usage.glyphs)), Unsafe: usage.unsafe})
+		if err != nil {
+			return nil, fmt.Errorf("subset font %s: %w", name, err)
+		}
+		if subset != nil {
 			updates[name] = subset
 		}
 	}

ofdgo_font_resource.go

@@ -0,0 +1,131 @@
+// 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 (
+	"fmt"
+	"slices"
+
+	"github.com/tdewolff/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
+	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 提供默认字体资源处理，不依赖Canvas绘图库
+type SFNTBackend struct{}
+
+// 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
+// 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
+	}
+	sfnt, err := font.ParseSFNT(data, 0)
+	if err != nil {
+		return nil, err
+	}
+	name := editorFontName(sfnt, font.NamePostScript, font.NameFull, font.NameFontFamily)
+	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: editorFontName(sfnt, font.NamePreferredFamily, font.NameFontFamily), Charset: "unicode", Bold: sfnt.Head.MacStyle[0], Italic: sfnt.Head.MacStyle[1], FixedWidth: sfnt.Post.IsFixedPitch != 0},
+		CanSubset: sfntSubsettable(sfnt),
+	}, nil
+}
+
+// sfntSubsettable 判断默认资源后端能否无损裁剪该字体
+// 入参: sfnt 已解析字体
+// 返回: bool 是否支持裁剪
+func sfntSubsettable(sfnt *font.SFNT) bool {
+	return sfnt.IsTrueType && !slices.ContainsFunc([]string{"fvar", "COLR", "CBDT", "sbix", "SVG "}, func(tag string) bool { return sfnt.Tables[tag] != nil })
+}
+
+// sfntResourceMetrics 隔离资源解析器的度量实现
+type sfntResourceMetrics struct{ *font.SFNT }
+
+// 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 fontSFNTData(f.SFNT) }
+
+// 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 subsetEditorFont(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 := newEditorFontUsage()
+	u.unsafe = usage.Unsafe
+	for _, char := range usage.Characters {
+		u.chars[char] = true
+	}
+	for _, glyph := range usage.Glyphs {
+		u.glyphs[glyph] = true
+	}
+	return subsetSourceFont(data, u), nil
+}
+
+// editorFontName 获取字体中的名称
+// 入参: sfnt 字体, names 名称类型，按顺序查找
+// 返回: string 字体名称
+func editorFontName(sfnt *font.SFNT, names ...font.NameID) string {
+	for _, name := range names {
+		for _, record := range sfnt.Name.Get(name) {
+			if value := record.String(); value != "" {
+				return value
+			}
+		}
+	}
+	return ""
+}

ofdgo_renderer_canvas.go

@@ -29,6 +29,20 @@ type CanvasBackend struct {
 	ColorSpace canvas.ColorSpace
 }
 
+// init 注册Canvas适配器和默认组合
+func init() {
+	if err := RegisterRenderBackend("canvas", defaultRenderBackends); err != nil {
+		panic(err)
+	}
+}
+
+// defaultRenderBackends 创建默认组合，调用方可按职责替换任意后端
+// 返回: RenderBackends 默认后端组合
+func defaultRenderBackends() RenderBackends {
+	backend := CanvasBackend{}
+	return RenderBackends{Resources: SFNTBackend{}, Fonts: backend, Geometry: backend, Compiler: backend, Raster: backend, SVG: backend, PDF: backend, EPS: backend}
+}
+
 // Name 返回后端标识
 // 返回: string 后端标识
 func (CanvasBackend) Name() string { return "canvas" }