总体实现：利用 cgo 基于pdfium(C库)实现pdf单页转图片，多页转图片后可拼接为长图
前期准备 linux上安装C库
1 创建文件目录结构 /opt/pdfium 下载pdfium-linux-x64,解压放入此目录下
2 为了保证编译的时候，pkg-config能够找到这个C语言库，需要为这个库生成一个描述文件，pdfium.pc，放入目录：/usr/lib64/pkgconfig。
3 为了运行时候能找到动态库，需要把so文件拷贝到/usr/lib目录下，赋予755权限，并执行ldconfig指令
CODE
package render
// #cgo pkg-config: pdfium
// #include "fpdfview.h"
// #include "fpdf_annot.h"
// #include "fpdf_edit.h"
// #include "fpdf_structtree.h"
import "C"
import (
"errors"
"fmt"
"github.com/nfnt/resize"
"image"
"image/color"
"image/draw"
"image/jpeg"
"io/ioutil"
"log"
"math"
"os"
"strconv"
"sync"
"unsafe"
)
// Document is good
type Document struct {
doc C.FPDF_DOCUMENT
data *[]byte // Keep a refrence to the data otherwise wierd stuff happens
}
const MaxWidth float64 = 600
var mutex = &sync.Mutex{}
// NewDocument shoud have docs
func NewDocument(data *[]byte) (*Document, error) {
mutex.Lock()
defer mutex.Unlock()
// doc := C.FPDF_LoadDocument(C.CString("in.pdf"), nil)
doc := C.FPDF_LoadMemDocument(
unsafe.Pointer(&((*data)[0])),
C.int(len(*data)),
nil)
if doc == nil {
var errMsg string
//defer C.FPDF_CloseDocument(doc)
errorcase := C.FPDF_GetLastError()
switch errorcase {
case C.FPDF_ERR_SUCCESS:
errMsg = "Success"
case C.FPDF_ERR_UNKNOWN:
errMsg = "Unknown error"
case C.FPDF_ERR_FILE:
errMsg = "Unable to read file"
case C.FPDF_ERR_FORMAT:
errMsg = "Incorrect format"
case C.FPDF_ERR_PASSWORD:
errMsg = "Invalid password"
case C.FPDF_ERR_SECURITY:
errMsg = "Invalid encryption"
case C.FPDF_ERR_PAGE:
errMsg = "Incorrect page"
default:
errMsg = "Unexpected error"
}
return nil, errors.New(errMsg)
}
return &Document{doc: doc, data: data}, nil
}
// GetPageCount shoud have docs
func (d *Document) GetPageCount() int {
mutex.Lock()
defer mutex.Unlock()
return int(C.FPDF_GetPageCount(d.doc))
}
// CloseDocument shoud have docs
func (d *Document) Close() {
mutex.Lock()
C.FPDF_CloseDocument(d.doc)
mutex.Unlock()
}
// RenderPage should have docs
func (d *Document) RenderPage(i int, dpi int) *image.RGBA {
mutex.Lock()
page := C.FPDF_LoadPage(d.doc, C.int(i))
scale := float64(dpi) / 72.0
imgWidth := C.FPDF_GetPageWidth(page) * C.double(scale)
imgHeight := C.FPDF_GetPageHeight(page) * C.double(scale)
// pixelBound := int(dpi * (3508 / 300))
// imgWidthRatio := float64(pixelBound) / float64(imgWidth)
// imgHeightRatio := float64(pixelBound) / float64(imgHeight)
// scaleFactor := math.Min(imgWidthRatio, imgHeightRatio)
scaleFactor := 1.0
width := C.int(imgWidth * C.double(scaleFactor))
height := C.int(imgHeight * C.double(scaleFactor))
alpha := C.FPDFPage_HasTransparency(page)
//创建空白位图对象
bitmap := C.FPDFBitmap_Create(width, height, alpha)
fillColor := 4294967295
if int(alpha) == 1 {
fillColor = 0
}
C.FPDFBitmap_FillRect(bitmap, 0, 0, width, height, C.ulong(fillColor))
C.FPDF_RenderPageBitmap(bitmap, page, 0, 0, width, height, 0, C.FPDF_ANNOT) //C.FPDF_ANNOT 彩色|C.FPDF_GRAYSCALE 黑白
p := C.FPDFBitmap_GetBuffer(bitmap)
img := image.NewRGBA(image.Rect(0, 0, int(width), int(height)))
img.Stride = int(C.FPDFBitmap_GetStride(bitmap))
mutex.Unlock()
// This takes a bit of time and I *think* we can do this without the lock
bgra := make([]byte, 4)
for y := 0; y < int(height); y++ {
for x := 0; x < int(width); x++ {
for i := range bgra {
bgra[i] = *((*byte)(p))
p = unsafe.Pointer(uintptr(p) + 1)
}
color := color.RGBA{B: bgra[0], G: bgra[1], R: bgra[2], A: bgra[3]}
img.SetRGBA(x, y, color)
}
}
mutex.Lock()
C.FPDFBitmap_Destroy(bitmap)
C.FPDF_ClosePage(page)
mutex.Unlock()
// should maybe return err
//println(C.FPDF_GetLastError())
return img
}
func InitLibrary() {
mutex.Lock()
C.FPDF_InitLibrary()
mutex.Unlock()
}
func DestroyLibrary() {
mutex.Lock()
C.FPDF_DestroyLibrary()
mutex.Unlock()
}
// FixSize 图片拼接之前计算 宽度尺寸
func FixSize(img1W, img2W int) (new1W, new2W int) {
var ( //为了方便计算，将两个图片的宽转为 float64
img1Width, img2Width = float64(img1W), float64(img2W)
ratio1, ratio2 float64
)
minWidth := math.Min(img1Width, img2Width) // 取出两张图片中宽度最小的为基准
if minWidth > 600 { // 如果最小宽度大于600，那么两张图片都需要进行缩放
ratio1 = MaxWidth / img1Width // 图片1的缩放比例
ratio2 = MaxWidth / img2Width // 图片2的缩放比例
// 原宽度 * 比例 = 新宽度
return int(img1Width * ratio1), int(img2Width * ratio2)
}
// 如果最小宽度小于600，那么需要将较大的图片缩放，使得两张图片的宽度一致
if minWidth == img1Width {
ratio2 = minWidth / img2Width // 图片2的缩放比例
return img1W, int(img2Width * ratio2)
}
ratio1 = minWidth / img1Width // 图片1的缩放比例
return int(img1Width * ratio1), img2W
}
// MergeImageNew 拼接图片
func MergeImageNew(basePath string, maskPath string, outImageName string) {
file1, _ := os.Open(basePath) //打开图片1
file2, _ := os.Open(maskPath) //打开图片2
defer file1.Close()
defer file2.Close()
// image.Decode 图片
var (
img1, img2 image.Image
err error
)
if img1, _, err = image.Decode(file1); err != nil {
log.Fatal(err)
return
}
if img2, _, err = image.Decode(file2); err != nil {
log.Fatal(err)
return
}
b1 := img1.Bounds()
b2 := img2.Bounds()
new1W, new2W := FixSize(b1.Max.X, b2.Max.X)
// 调用resize库进行图片缩放(高度填0，resize.Resize函数中会自动计算缩放图片的宽高比)
m1 := resize.Resize(uint(new1W), 0, img1, resize.Lanczos3)
m2 := resize.Resize(uint(new2W), 0, img2, resize.Lanczos3)
// 将两个图片合成一张
newWidth := m1.Bounds().Max.X //新宽度 = 随意一张图片的宽度
newHeight := m1.Bounds().Max.Y + m2.Bounds().Max.Y // 新图片的高度为两张图片高度的和
newImg := image.NewNRGBA(image.Rect(0, 0, newWidth, newHeight)) //创建一个新RGBA图像
draw.Draw(newImg, newImg.Bounds(), m1, m1.Bounds().Min, draw.Over) //画上第一张缩放后的图片
draw.Draw(newImg, newImg.Bounds(), m2, m2.Bounds().Min.Sub(image.Pt(0, m1.Bounds().Max.Y)), draw.Over) //画上第二张缩放后的图片（这里需要注意Y值的起始位置）
// 保存文件
os.Remove(outImageName + ".jpg")
imgFile, _ := os.Create(outImageName + ".jpg")
defer imgFile.Close()
jpeg.Encode(imgFile, newImg, &jpeg.Options{100})
}
// PdfToImg PDF 转 图片 并拼接后保存
func PdfToImg(filePath string,outName string){
data, _ := ioutil.ReadFile(filePath)
outImgName := "./outImg/"+outName
//C.FPDF_InitLibrary()
InitLibrary()
d, err := NewDocument(&data)
if err != nil {
println(err)
} else {
count := d.GetPageCount()
img0 := d.RenderPage(0, 600)
fb, _ := os.OpenFile(outImgName+".jpg", os.O_WRONLY|os.O_CREATE, 0600)
jpeg.Encode(fb, img0, nil)
fb.Close()
imgSlice := make([]string, 0, 30)
for i := 0; i < count; i++ {
img := d.RenderPage(i, 600)
f, _ := os.OpenFile(outImgName+strconv.Itoa(i)+".jpg", os.O_WRONLY|os.O_CREATE, 0600)
if errSImg := jpeg.Encode(f, img, nil); errSImg != nil {
fmt.Println(errSImg)
}
f.Close()
imgSlice = append(imgSlice, outImgName+strconv.Itoa(i)+".jpg")
}
if len(imgSlice) > 1 {
for j := 1; j < count; j++ {
MergeImageNew(outImgName+".jpg", outImgName+strconv.Itoa(j)+".jpg", outImgName)
os.Remove(outImgName+strconv.Itoa(j)+".jpg") //删除单图
}
}
os.Remove(outImgName+strconv.Itoa(0)+".jpg")
d.Close()
}
DestroyLibrary()
}