feat(后端架构): 完善后端解耦

ofdgo_renderer_output_canvas.go

@@ -0,0 +1,140 @@
+// 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 (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+
+	"github.com/tdewolff/canvas"
+	"github.com/tdewolff/canvas/renderers/pdf"
+	"github.com/tdewolff/canvas/renderers/ps"
+	"github.com/tdewolff/canvas/renderers/svg"
+)
+
+// RenderSVG 使用canvas输出SVG，按模式保留资源和对象分组
+// 入参: r 渲染器, page 页面内容, writer 输出流, mode 资源模式
+// 返回: SVGResources 外部资源, error 错误信息
+func (CanvasBackend) RenderSVG(r *Renderer, page *PageContent, writer io.Writer, mode SVGMode) (SVGResources, error) {
+	switch mode {
+	case SVGExternalFonts:
+		return r.renderSVGResources(page, writer, false, false)
+	case SVGExternalResources:
+		return r.renderSVGResources(page, writer, true, false)
+	case SVGObjects:
+		return r.renderSVGResources(page, writer, true, true)
+	case SVGEmbedded:
+		c, err := r.renderCanvasPage(page)
+		if err != nil {
+			return SVGResources{}, err
+		}
+		buffer := bufio.NewWriter(writer)
+		renderer := svg.New(buffer, c.W, c.H, nil)
+		c.RenderTo(renderer)
+		if err := renderer.Close(); err != nil {
+			return SVGResources{}, err
+		}
+		return SVGResources{}, buffer.Flush()
+	default:
+		return SVGResources{}, fmt.Errorf("unsupported SVG mode %d", mode)
+	}
+}
+
+// RenderEPS 使用canvas输出单页EPS
+// 入参: r 渲染器, page 页面内容, writer 输出流
+// 返回: error 错误信息
+func (CanvasBackend) RenderEPS(r *Renderer, page *PageContent, writer io.Writer) error {
+	c, err := r.renderCanvasPage(page)
+	if err != nil {
+		return err
+	}
+	options := ps.DefaultOptions
+	options.Format = ps.EncapsulatedPostScript
+	buffer := bufio.NewWriter(writer)
+	renderer := ps.New(buffer, c.W, c.H, &options)
+	c.RenderTo(renderer)
+	if err := renderer.Close(); err != nil {
+		return err
+	}
+	return buffer.Flush()
+}
+
+// RenderPDF 使用canvas输出PDF，保留导航与文字并复用输出缓冲
+// 入参: r 渲染器, pages 页面列表, writer 输出流, progress 页面处理进度
+// 返回: error 错误信息
+func (CanvasBackend) RenderPDF(r *Renderer, pages []RenderDocumentPage, writer io.Writer, progress func(int, int) error) error {
+	if len(pages) == 0 {
+		return fmt.Errorf("no pages found")
+	}
+	navigation, err := newPDFNavigation(r, r.Reader.doc, pages)
+	if err != nil {
+		return err
+	}
+	buf, direct := writer.(*bytes.Buffer)
+	if !direct {
+		buf = &bytes.Buffer{}
+	}
+	start := buf.Len()
+	p := pdf.New(buf, pages[0].Box.W, pages[0].Box.H, nil)
+	renderer := &pdfRenderer{PDF: p, glyphPaths: make(map[*canvas.Path]*canvas.Path)}
+	var info DocInfo
+	if docInfo, err := r.Reader.DocInfo(); err == nil {
+		info = *docInfo
+	}
+	p.SetInfo(info.Title, info.Subject, "", info.Author, "xiaoqidun/ofdgo")
+	for i, page := range pages {
+		if i > 0 {
+			p.NewPage(page.Box.W, page.Box.H)
+		}
+		navigation.apply(p, i)
+		if err := r.renderCanvasPageToContext(canvas.NewContext(renderer), page.Content, !r.TransparentBackground); err != nil {
+			buf.Truncate(start)
+			return fmt.Errorf("failed to render page %d: %w", i+1, err)
+		}
+		pages[i].Content = nil
+		if progress != nil {
+			if err := progress(i+1, len(pages)); err != nil {
+				buf.Truncate(start)
+				return err
+			}
+		}
+	}
+	if err := p.Close(); err != nil {
+		buf.Truncate(start)
+		return err
+	}
+	data := replacePDFProducer(buf.Bytes()[start:])
+	if direct {
+		return nil
+	}
+	_, err = writer.Write(data)
+	return err
+}
+
+// replacePDFProducer 替换PDF的Producer属性
+// 入参: data PDF字节数据
+// 返回: []byte 替换后的PDF字节数据
+func replacePDFProducer(data []byte) []byte {
+	old := []byte("/Producer(tdewolff/canvas)")
+	idx := bytes.LastIndex(data, old)
+	if idx < 0 {
+		return data
+	}
+	dst := []byte("/Producer(xiaoqidun/ofdgo)")
+	copy(data[idx:idx+len(old)], dst)
+	return data
+}