feat(转换能力): 完善PDF转换与链接保留，优化大型文档处理，新增转换提示

ofdgo_pdf_link.go

@@ -0,0 +1,150 @@
+// 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"
+
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// links 将无外观链接转换为OFD点击区域，其他注解或外观返回不支持错误
+// 入参: page PDF页面
+// 返回: error 错误信息
+func (p *pdfImporter) links(page *pdfgo.Page) error {
+	annotations, err := page.Annotations()
+	if err != nil {
+		return err
+	}
+	for _, annotation := range annotations {
+		dict := annotation.Dictionary
+		if annotation.Subtype != "Link" {
+			return &pdfgo.UnsupportedError{Feature: "annotation " + string(annotation.Subtype)}
+		}
+		for _, key := range []pdfgo.Name{"AP", "AA", "BS", "QuadPoints", "OC"} {
+			if dict[key] != nil {
+				return &pdfgo.UnsupportedError{Feature: fmt.Sprintf("link annotation field %q", key)}
+			}
+		}
+		if value, err := p.reader.Resolve(dict["F"]); err != nil {
+			return err
+		} else if value != nil {
+			flags, ok := value.(pdfgo.Integer)
+			if !ok {
+				return fmt.Errorf("invalid PDF annotation flags")
+			}
+			if flags != 0 && flags != 4 {
+				return &pdfgo.UnsupportedError{Feature: "link annotation flags"}
+			}
+		}
+		border, err := p.reader.Resolve(dict["Border"])
+		if err != nil {
+			return err
+		}
+		array, ok := border.(pdfgo.Array)
+		if !ok || len(array) != 3 || (array[2] != pdfgo.Integer(0) && array[2] != pdfgo.Real(0)) {
+			return &pdfgo.UnsupportedError{Feature: "visible link border"}
+		}
+		action := Action{Event: "CLICK"}
+		target := dict["Dest"]
+		if dict["A"] != nil {
+			value, err := p.reader.Resolve(dict["A"])
+			if err != nil {
+				return err
+			}
+			a, ok := value.(pdfgo.Dictionary)
+			if !ok {
+				return fmt.Errorf("invalid PDF link action")
+			}
+			if a["Next"] != nil {
+				return &pdfgo.UnsupportedError{Feature: "chained link actions"}
+			}
+			switch a["S"] {
+			case pdfgo.Name("GoTo"):
+				target = a["D"]
+			case pdfgo.Name("URI"):
+				value, err := p.reader.Resolve(a["URI"])
+				if err != nil {
+					return err
+				}
+				uri, ok := value.(pdfgo.String)
+				if !ok {
+					return fmt.Errorf("invalid PDF URI")
+				}
+				isMap, err := p.reader.Resolve(a["IsMap"])
+				if err != nil {
+					return err
+				}
+				if isMap != nil && isMap != pdfgo.Boolean(false) && isMap != pdfgo.Boolean(true) {
+					return fmt.Errorf("invalid PDF URI image map flag")
+				}
+				if isMap == pdfgo.Boolean(true) {
+					return &pdfgo.UnsupportedError{Feature: "URI image map"}
+				}
+				base, err := p.reader.BaseURI()
+				if err != nil {
+					return err
+				}
+				action.URI = &URI{URI: string(uri), Base: base}
+			default:
+				return &pdfgo.UnsupportedError{Feature: "link action"}
+			}
+		}
+		if action.URI == nil {
+			destination, err := p.reader.ReadDestination(target)
+			if err != nil {
+				return err
+			}
+			targetPage := p.pages[destination.Page]
+			if targetPage == nil {
+				return fmt.Errorf("PDF destination page missing")
+			}
+			matrix, _, _ := pdfPageMatrix(targetPage)
+			dest := &Dest{Type: string(destination.Mode), PageID: p.pageIDs[destination.Page]}
+			if destination.Mode == "XYZ" {
+				values := [3]float64{}
+				for n, v := range destination.Parameters {
+					switch v := v.(type) {
+					case pdfgo.Integer:
+						values[n] = float64(v)
+					case pdfgo.Real:
+						values[n] = float64(v)
+					case nil:
+						if n < 2 {
+							return &pdfgo.UnsupportedError{Feature: "retained destination coordinates"}
+						}
+					}
+				}
+				point := matrix.Apply(pdfgo.Point{X: values[0], Y: values[1]})
+				dest.Left, dest.Top, dest.Zoom = point.X, point.Y, values[2]
+			} else if destination.Mode != "Fit" {
+				return &pdfgo.UnsupportedError{Feature: "destination mode " + string(destination.Mode)}
+			}
+			action.Goto = &Goto{Dest: dest}
+		}
+		b := annotation.Rect
+		box := pdfBounds([]pdfgo.Point{p.matrix.Apply(pdfgo.Point{X: b.XMin, Y: b.YMin}), p.matrix.Apply(pdfgo.Point{X: b.XMax, Y: b.YMax})})
+		object, err := NewShape(ShapeRectangle, box)
+		if err != nil {
+			return err
+		}
+		no := false
+		object.Fill, object.Stroke = &no, &no
+		object.Actions = []Action{action}
+		p.objects = append(p.objects, GraphicObject{Type: "PathObject", PathObject: object})
+		p.report.Links++
+	}
+	return nil
+}