feat(文字图像): 修复文字定位及图像导出

ofdgo_renderer_pdf_images.go

@@ -0,0 +1,106 @@
+// 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"
+
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// preserveImages 按实际绘制顺序恢复颜色及透明度精度，不依赖后端资源命名或对象编号
+// 入参: ctx 取消上下文, data 后端PDF数据
+// 返回: []byte 保留图像精度的PDF数据, error 资源或写入错误
+func (r *pdfRenderer) preserveImages(ctx context.Context, data []byte) ([]byte, error) {
+	if !r.exactImages {
+		return data, nil
+	}
+	reader, err := pdfgo.NewReader(bytes.NewReader(data), int64(len(data)))
+	if err != nil {
+		return nil, err
+	}
+	defer reader.Close()
+	images := make(map[pdfgo.Reference]image.Image)
+	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++
+		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 nil, err
+	}
+	if pages != len(r.images) {
+		return nil, fmt.Errorf("PDF output page missing")
+	}
+	var result bytes.Buffer
+	if _, err := reader.ReplaceImagesTo(ctx, &result, images); err != nil {
+		return nil, err
+	}
+	return result.Bytes(), nil
+}