feat(内存占用): 复用SVG字体资源，减少多页阅读的传输量和内存开销

ofdgo_renderer_svg.go

@@ -0,0 +1,93 @@
+// 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 (
+	"crypto/sha256"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/tdewolff/canvas"
+	"github.com/tdewolff/canvas/renderers/svg"
+)
+
+// SVGFont SVG引用的字体资源，Name为CSS字体族标识，Data为只读字体数据
+type SVGFont struct {
+	Name   string
+	Weight int
+	Style  string
+	Data   []byte
+}
+
+// svgFontRenderer 分离字体资源的SVG渲染器
+type svgFontRenderer struct {
+	*svg.SVG
+	renderer *Renderer
+	fonts    []SVGFont
+	seen     map[string]bool
+	styles   strings.Builder
+}
+
+// RenderToSVGWithFonts 渲染为SVG并返回页面引用的字体资源，不在SVG中嵌入字体
+// 入参: page 页面内容, writer 输出流
+// 返回: []SVGFont 字体资源，可按Name复用并按Weight、Style注册，error 错误信息
+func (r *Renderer) RenderToSVGWithFonts(page *PageContent, writer io.Writer) ([]SVGFont, error) {
+	c, err := r.renderPage(page)
+	if err != nil {
+		return nil, err
+	}
+	options := svg.DefaultOptions
+	options.EmbedFonts = false
+	s := &svgFontRenderer{
+		SVG:      svg.New(writer, c.W, c.H, &options),
+		renderer: r,
+		seen:     make(map[string]bool),
+	}
+	c.RenderTo(s)
+	s.SetCustomStyle(s.styles.String())
+	return s.fonts, s.Close()
+}
+
+// RenderText 绘制文字并记录实际使用的字体资源
+// 入参: text 文字对象, m 变换矩阵
+func (s *svgFontRenderer) RenderText(text *canvas.Text, m canvas.Matrix) {
+	if text.Empty() {
+		return
+	}
+	font := text.MostCommonFontFace().Font
+	resource, ok := s.renderer.svgFontCache[font]
+	if !ok {
+		data := font.SFNT.Write()
+		resource = SVGFont{
+			Name:   fmt.Sprintf("ofdgo-%x-%d", sha256.Sum256(data), font.Style()),
+			Weight: font.Style().CSS(),
+			Style:  "normal",
+			Data:   data,
+		}
+		if font.Style().Italic() {
+			resource.Style = "italic"
+		}
+		s.renderer.svgFontCache[font] = resource
+	}
+	if !s.seen[resource.Name] {
+		s.seen[resource.Name] = true
+		s.fonts = append(s.fonts, resource)
+		fmt.Fprintf(&s.styles, ".%s{font-family:%s!important}", resource.Name, resource.Name)
+	}
+	s.SetClass(resource.Name)
+	s.SVG.RenderText(text, m)
+	s.SetClass()
+}