feat(后端架构): 完善后端解耦

ofdgo_renderer_font_canvas.go

@@ -0,0 +1,135 @@
+// 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"
+	"path"
+
+	"github.com/tdewolff/canvas"
+	"github.com/tdewolff/font"
+)
+
+// ResolveFont 按需加载字体资源，保留内嵌数据及外部字体的名称、样式和集合索引匹配
+// 入参: r 渲染器, id 字体标识, exact 是否禁止无关回退
+// 返回: ResolvedFont 字体与来源, error 字体不可用错误
+func (CanvasBackend) ResolveFont(r *Renderer, id string, exact bool) (ResolvedFont, error) {
+	definition := r.Reader.fontCache[id]
+	if definition == nil && !r.Reader.fontResourcesRead && r.Reader.OFD != nil {
+		if _, err := r.Reader.Fonts(); err != nil {
+			return ResolvedFont{}, err
+		}
+		definition = r.Reader.fontCache[id]
+	}
+	if definition == nil {
+		if exact {
+			return ResolvedFont{}, fmt.Errorf("font %q not found", id)
+		}
+		return r.canvasFallbackFont(), nil
+	}
+	if definition.FontFile != "" {
+		data, err := r.Reader.FontData(id)
+		if err != nil {
+			return ResolvedFont{}, err
+		}
+		face, err := r.Reader.embeddedFontFace(*definition)
+		if err != nil {
+			return ResolvedFont{}, err
+		}
+		return ResolvedFont{Data: data, Source: path.Base(definition.FontFile), Face: face, Exact: true}, nil
+	}
+	style := canvasFontStyle(definition)
+	if source, family := r.fontSourceMatch(id, definition, exact); family != nil {
+		sfnt := family.Face(12, style).Font.SFNT
+		face := fontFaceInfo(sfnt.Tables["name"], source.face)
+		r.fontSourceUsed[id] = source
+		return ResolvedFont{Data: fontSFNTData(sfnt), Source: source.name, Face: &face, Exact: source.exact}, nil
+	}
+	if !exact {
+		return r.canvasFallbackFont(), nil
+	}
+	return ResolvedFont{}, fmt.Errorf("font %q is unavailable", definition.FontName)
+}
+
+// canvasFallbackFont 按需加载默认阅读字体，不用于精确编辑匹配
+// 返回: ResolvedFont 默认字体，未安装时数据为空
+func (r *Renderer) canvasFallbackFont() ResolvedFont {
+	if r.fontFamily == nil {
+		r.initCanvasFonts()
+	}
+	if r.defaultFontLoaded {
+		return ResolvedFont{Data: fontSFNTData(r.fontFamily.Face(12, canvas.FontRegular).Font.SFNT)}
+	}
+	return ResolvedFont{}
+}
+
+// OpenFont 解析独立SFNT数据，度量与原有编辑排版保持一致
+// 入参: data 字体数据
+// 返回: FontMetrics 字体度量, error 解析错误
+func (CanvasBackend) OpenFont(data []byte) (FontMetrics, error) {
+	sfnt, err := font.ParseSFNT(data, 0)
+	if err != nil {
+		return nil, err
+	}
+	return canvasFontMetrics{sfnt}, nil
+}
+
+// canvasFontMetrics 保留默认字体度量，写出时不更新原始时间
+type canvasFontMetrics struct {
+	*font.SFNT
+}
+
+// Write 返回字体数据，不修改字体元信息
+// 返回: []byte 独立SFNT数据
+func (f canvasFontMetrics) Write() []byte {
+	return fontSFNTData(f.SFNT)
+}
+
+// canvasFontState 保存默认适配器的字体与字形缓存，不向后端接口暴露绘图库类型
+type canvasFontState struct {
+	fontFamily         *canvas.FontFamily
+	defaultFontLoaded  bool
+	fontMap            map[string]*canvas.FontFamily
+	fontGIDMap         map[string]map[uint16]rune
+	fontCIDMap         map[string]map[uint16]rune
+	fontCache          map[fontCacheKey]*canvas.FontFamily
+	svgFontCache       map[*canvas.Font]SVGFont
+	fontSourceCache    map[string][]fontSource
+	fontSourceUsed     map[string]fontSource
+	fontDirCandidates  map[string][]fontFileCandidate
+	fontFSCandidates   map[int][]fontFileCandidate
+	textGlyphPathCache map[textGlyphPathCacheKey]textGlyphPathCacheValue
+}
+
+// resetFontCache 重置字体匹配、加载和字形缓存
+func (r *Renderer) resetFontCache() {
+	r.resolvedFonts = make(map[resolvedFontKey]resolvedFontResult)
+	r.fontMap = make(map[string]*canvas.FontFamily)
+	r.fontGIDMap = make(map[string]map[uint16]rune)
+	r.fontCIDMap = make(map[string]map[uint16]rune)
+	r.fontCache = make(map[fontCacheKey]*canvas.FontFamily)
+	r.svgFontCache = make(map[*canvas.Font]SVGFont)
+	r.fontSourceCache = make(map[string][]fontSource)
+	r.fontSourceUsed = make(map[string]fontSource)
+	r.fontDirCandidates = make(map[string][]fontFileCandidate)
+	r.fontFSCandidates = make(map[int][]fontFileCandidate)
+	r.textGlyphPathCache = make(map[textGlyphPathCacheKey]textGlyphPathCacheValue)
+}
+
+// initCanvasFonts 初始化Canvas默认字体
+func (r *Renderer) initCanvasFonts() {
+	r.fontFamily = canvas.NewFontFamily("default")
+	r.defaultFontLoaded = r.loadDefaultFonts()
+}