feat(目录压缩): 规范目录导航，优化压缩写出

ofdgo_renderer_pdf_write.go

@@ -0,0 +1,162 @@
+// 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 (
+	"bytes"
+	"context"
+	"fmt"
+	"image"
+	"io"
+
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// writePDF 合并图像、导航修正及压缩，直接写出最终PDF
+// 入参: ctx 取消上下文, data 后端PDF数据, writer 输出流, optimization 优化配置
+// 返回: error 资源、压缩或写入错误
+func (r *pdfRenderer) writePDF(ctx context.Context, data []byte, writer io.Writer, optimization pdfgo.OptimizeOptions) error {
+	if r.imageError != nil {
+		return r.imageError
+	}
+	exactLinks := r.navigation != nil && r.navigation.exactLinks
+	if !r.exactImages && !exactLinks && optimization.Compression.Mode == CompressionUnchanged {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		n, err := writer.Write(data)
+		if err == nil && n != len(data) {
+			err = io.ErrShortWrite
+		}
+		return err
+	}
+	reader, err := pdfgo.NewReader(bytes.NewReader(data), int64(len(data)))
+	if err != nil {
+		return err
+	}
+	defer reader.Close()
+	if !r.exactImages && !exactLinks {
+		_, err := reader.OptimizeTo(ctx, writer, optimization)
+		return err
+	}
+	images := make(map[pdfgo.Reference]image.Image)
+	links := make(map[pdfgo.AnnotationLocation]pdfgo.LinkRegion)
+	references := make([]pdfgo.Reference, len(r.images))
+	pages := 0
+	err = reader.WalkPages(ctx, func(index int, page *pdfgo.Page) error {
+		if index >= len(r.images) {
+			return fmt.Errorf("unexpected PDF output page")
+		}
+		pages++
+		references[index] = page.Reference
+		if exactLinks {
+			annotations, err := page.AnnotationsContext(ctx)
+			if err != nil {
+				return err
+			}
+			expected := r.navigation.Link[index]
+			if len(annotations) != len(expected) {
+				return fmt.Errorf("PDF output link count differs")
+			}
+			for i, link := range expected {
+				if annotations[i].Subtype != pdfgo.Name("Link") {
+					return fmt.Errorf("unexpected PDF output annotation")
+				}
+				if link.Region != nil {
+					links[pdfgo.AnnotationLocation{Page: page.Reference, Index: i}] = *link.Region
+				}
+			}
+		}
+		if !r.exactImages {
+			return nil
+		}
+		value, err := reader.Resolve(page.Resources["XObject"])
+		if err != nil {
+			return err
+		}
+		resources, _ := value.(pdfgo.Dictionary)
+		var content bytes.Buffer
+		if _, err := page.WriteContent(ctx, &content); err != nil {
+			return err
+		}
+		position := 0
+		if err := pdfgo.WalkOperations(ctx, content.Bytes(), func(operation pdfgo.Operation) error {
+			if operation.Operator != "Do" {
+				return nil
+			}
+			if len(operation.Operands) != 1 || position >= len(r.images[index]) {
+				return fmt.Errorf("unexpected PDF output image")
+			}
+			name, ok := operation.Operands[0].(pdfgo.Name)
+			if !ok {
+				return fmt.Errorf("invalid PDF output image name")
+			}
+			ref, ok := resources[name].(pdfgo.Reference)
+			if !ok {
+				return fmt.Errorf("invalid PDF output image reference")
+			}
+			original := r.images[index][position]
+			position++
+			if original == nil {
+				return nil
+			}
+			image, err := reader.ReadImage(ref)
+			if err != nil {
+				return err
+			}
+			if image.Width != original.Bounds().Dx() || image.Height != original.Bounds().Dy() {
+				return fmt.Errorf("PDF output image dimensions differ")
+			}
+			if previous := images[ref]; previous != nil && previous != original {
+				return fmt.Errorf("PDF output image reference conflicts")
+			}
+			images[ref] = original
+			return nil
+		}); err != nil {
+			return err
+		}
+		if position != len(r.images[index]) {
+			return fmt.Errorf("PDF output image missing")
+		}
+		return nil
+	})
+	if err != nil {
+		return err
+	}
+	if pages != len(r.images) {
+		return fmt.Errorf("PDF output page missing")
+	}
+	options := pdfgo.RewriteOptions{Images: images, ImageOptions: pdfgo.ImageWriteOptions{PreblendBinary: true}, LinkRegions: links, Optimization: optimization}
+	if exactLinks {
+		if err := r.navigation.destinations(ctx, reader, references, &options); err != nil {
+			return err
+		}
+	}
+	for ref, original := range images {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		pixels, err := imagePixelData(original)
+		if err != nil {
+			return err
+		}
+		if pixels == nil || pixels.Bounds() != original.Bounds() {
+			return fmt.Errorf("PDF output image pixel bounds differ")
+		}
+		images[ref] = pixels
+	}
+	_, err = reader.RewriteTo(ctx, writer, options)
+	return err
+}