Qt显示pdf系列4——封装pdfium库为动态库，显示pdf

 承接上篇，pdfium的lib文件是已经编译出来了，理论上已经可以开始直接用了，官方提供的测试demo中基本上介绍了用法的整套流程，你可以选择导出一页页的（图片）文件，也可以直接取出Buffer丢给支持图形库去渲染。

序

 但是需要注意的是，他在实际使用中依旧有很多不便：
1、我们能够编译出来的只有vs2015或以上版本的lib，如果我们需要在别的ide中引用，那么就可能不行。
2、编译出来的lib一共24个，所以确定要在项目中，光pdf库就引用这么多个吗= =。

 解决方式：基于这些lib的基础上，再包一层，把他编译成动态库，接口用纯C语言，不仅简洁，而且理论上说是跨平台的。

 关于动态库，只简单说几句，不了解可以自己查：静态链接库（.lib）cpp里所有代码被被编译成2进制文件，使用时直接会连接到你的项目中，而动态链接库，里面是你项目的代码，也不会编译进你的程序中。

 开发环境：windows7+vs2015

一、新建项目:

 打开vs2015，新建一个c++的win32项目，当然，你也可以直接新建成空项目，然后在设置里手动修改输出方式为dll。这里我的项目叫pdf

二、封装pdfium库:

1、把上篇编译出来的pdfium库的lib和头文件整理好，并添加到刚才新建的项目中去：


2、在项目中新建PdfManager.h,PdfManager.cpp。开始写代码：
PdfManager.h：

#ifndef _PDF_MANAGER_H_#define _PDF_MANAGER_H_//filename是文件名，需要唯一，dat是打开的pdf的内容（可以用fstream打开，以二进制形式），length是pdf长度extern "C" _declspec(dllexport) bool __stdcall PDFMANAGER_Loadpdf(const char* filename, char* dat, int length); //加载pdf(即加载已经打开的pdf)//filename是文件名，关闭该pdfextern "C" _declspec(dllexport) bool __stdcall PDFMANAGER_Closepdf(const char* filename); //关闭pdf//filename是文件名，关闭该pdf，page是需要显示页数，width是宽，height是高，size是当前页的大小，outBmp是是否导出bmp文件，返回该页bufferextern "C" _declspec(dllexport) char* __stdcall PDFMANAGER_LoadPage(const char* filename, int page, float& width, float& height, int& size, bool OutBmp);//加载页面//filename是文件名，关闭该页面，打开后需要关闭，否则会内存泄漏extern "C" _declspec(dllexport) void __stdcall PDFMANAGER_ClosePage(const char* filename, int page); //关闭页面//获取总页数extern "C" _declspec(dllexport) int __stdcall PDFMANAGER_GetPageCount(const char* filename);//获取下一页该渲染的页extern "C" _declspec(dllexport) int __stdcall PDFMANAGER_GetCurrentPage(const char* filename);#endif

PdfManager.cpp：

#include "PdfManager.h"#include "fpdfview.h"#include <limits.h>#include <stdlib.h>#include <string.h>#include <memory>#include <map>#include <sstream>#include <string>#include <utility>#include <vector>#include "fpdf_dataavail.h"#include "fpdf_edit.h"#include "fpdf_ext.h"#include "fpdf_formfill.h"#include "fpdf_text.h"#include <functional>#include <fstream>enum OutputFormat{    OUTPUT_STR,    OUTPUT_BMP,};struct Options{    Options() :pages(false), output_format(OUTPUT_BMP) {}    bool pages; //是否指定范围    OutputFormat output_format;    int first_page = 0; //起始页数    int last_page = 0; //终止页数    int currentpage = 0; //要打印的页面    float width = 0; //目标宽度    float height = 0; //目标高度};FPDF_BOOL Is_Data_Avail(FX_FILEAVAIL* avail, size_t offset, size_t size){    return true;}class PDFManager{    static std::string WriteBmp(int num,        const void* buffer,        int stride,        int width,        int height)    {        if (stride < 0 || width < 0 || height < 0)            return false;        if (height > 0 && width > INT_MAX / height)            return false;        int out_len = stride * height;        if (out_len > INT_MAX / 3)            return "";        char filename[256];        snprintf(filename, sizeof(filename), "%d.bmp", num);        FILE* fp = fopen(filename, "wb");        if (!fp)            return "";        BITMAPINFO bmi = {};        bmi.bmiHeader.biSize = sizeof(bmi) - sizeof(RGBQUAD);        bmi.bmiHeader.biWidth = width;        bmi.bmiHeader.biHeight = -height;  // top-down image        bmi.bmiHeader.biPlanes = 1;        bmi.bmiHeader.biBitCount = 32;        bmi.bmiHeader.biCompression = BI_RGB;        bmi.bmiHeader.biSizeImage = 0;        BITMAPFILEHEADER file_header = {};        file_header.bfType = 0x4d42;        file_header.bfSize = sizeof(file_header) + bmi.bmiHeader.biSize + out_len;        file_header.bfOffBits = file_header.bfSize - out_len;        fwrite(&file_header, sizeof(file_header), 1, fp);        fwrite(&bmi, bmi.bmiHeader.biSize, 1, fp);        fwrite(buffer, out_len, 1, fp);        fclose(fp);        return std::string(filename);    }    struct FPDF_FORMFILLINFO_PDFiumTest : public FPDF_FORMFILLINFO    {        // Hold a map of the currently loaded pages in order to avoid them        // to get loaded twice.        std::map<int, FPDF_PAGE> loaded_pages;        // Hold a pointer of FPDF_FORMHANDLE so that PDFium app hooks can        // make use of it.        FPDF_FORMHANDLE form_handle;    };    struct AvailDeleter    {        inline void operator()(FPDF_AVAIL avail) const        {            FPDFAvail_Destroy(avail);        }    };    static FPDF_FORMFILLINFO_PDFiumTest* ToPDFiumTestFormFillInfo(FPDF_FORMFILLINFO* form_fill_info)    {        return static_cast<FPDF_FORMFILLINFO_PDFiumTest*>(form_fill_info);    }    FPDF_PAGE GetPageForIndex(FPDF_FORMFILLINFO* param,        FPDF_DOCUMENT& doc,        int index)    {        FPDF_FORMFILLINFO_PDFiumTest* form_fill_info =            ToPDFiumTestFormFillInfo(param);        auto& loaded_pages = form_fill_info->loaded_pages;        auto iter = loaded_pages.find(index);        if (iter != loaded_pages.end())            return iter->second;        FPDF_PAGE page = FPDF_LoadPage(doc, index);        if (!page)            return nullptr;        FPDF_FORMHANDLE& form_handle = form_fill_info->form_handle;        FORM_OnAfterLoadPage(page, form_handle);        FORM_DoPageAAction(page, form_handle, FPDFPAGE_AACTION_OPEN);        loaded_pages[index] = page;        return page;    }    char* RenderPage(FPDF_DOCUMENT& doc,        FPDF_FORMFILLINFO_PDFiumTest& form_fill_info        , float& width, float& height,        const Options& options,        int& size)    {        FPDF_PAGE page = GetPageForIndex(&form_fill_info, doc, options.currentpage);        if (!page)        {            return nullptr;        }        FPDF_TEXTPAGE text_page = FPDFText_LoadPage(page);        double scale = 1.0;        int widthdraw = static_cast<int>(FPDF_GetPageWidth(page) * scale);        int heightdraw = static_cast<int>(FPDF_GetPageHeight(page) * scale);        if (options.width > 0 && options.height > 0)        {            if (options.width > options.height)            {                double scalewidth = (double)options.height / (double)heightdraw;                heightdraw = options.height;                widthdraw = scalewidth * widthdraw;            }            else            {                double scaleheight = (double)options.width / (double)widthdraw;                widthdraw = options.width;                heightdraw = scaleheight * heightdraw;            }        }        //else        //{        //  widthdraw = static_cast<int>(FPDF_GetPageWidth(page) * scale);        //  heightdraw = static_cast<int>(FPDF_GetPageHeight(page) * scale);        //}        int alpha = FPDFPage_HasTransparency(page) ? 1 : 0;        FPDF_BITMAP bitmap = FPDFBitmap_Create(widthdraw, heightdraw, alpha);        const char* buffer = nullptr;        char* rtnBuffer = nullptr;        int out_len = 0;        if (bitmap)        {            FPDF_DWORD fill_color = alpha ? 0x00000000 : 0xFFFFFFFF;            FPDFBitmap_FillRect(bitmap, 0, 0, widthdraw, heightdraw, fill_color);            FPDF_RenderPageBitmap(bitmap, page, 0, 0, widthdraw, heightdraw, 0, FPDF_ANNOT | FPDF_REVERSE_BYTE_ORDER);            //FPDF_FFLDraw(form, bitmap, page, 0, 0, width, height, 0, FPDF_ANNOT | FPDF_REVERSE_BYTE_ORDER);            int stride = FPDFBitmap_GetStride(bitmap);            int strheight = FPDFBitmap_GetHeight(bitmap);            buffer = reinterpret_cast<const char*>(FPDFBitmap_GetBuffer(bitmap));            //开辟新内存            size = stride * strheight;            rtnBuffer = new char[size];            memset(rtnBuffer, 0, size);            memcpy(rtnBuffer, buffer, size);            width = FPDFBitmap_GetWidth(bitmap);            height = FPDFBitmap_GetHeight(bitmap);            Pages_.insert(std::make_pair(options.currentpage, rtnBuffer));            switch (options.output_format)            {            case OUTPUT_BMP:                WriteBmp(options.currentpage, buffer, stride, widthdraw, heightdraw);                break;            default:                break;            }            FPDFBitmap_Destroy(bitmap);        }        /*else            fprintf(stderr, "Page was too large to be rendered.\n");*/        form_fill_info.loaded_pages.erase(options.currentpage);        /*FORM_DoPageAAction(page, form, FPDFPAGE_AACTION_CLOSE);        FORM_OnBeforeClosePage(page, form);*/        FPDFText_ClosePage(text_page);        FPDF_ClosePage(page);        return rtnBuffer;    }    class TestLoader    {    public:        TestLoader(const char* buff, size_t len)        {            m_pBuf = new char[len];            memcpy(m_pBuf, buff, len);            m_Len = len;        }        ~TestLoader()        {            delete[]m_pBuf;        }        static int GetBlock(void* param,            unsigned long pos,            unsigned char* pBuf,            unsigned long size)        {            TestLoader* pLoader = static_cast<TestLoader*>(param);            if (pos + size < pos || pos + size > pLoader->m_Len)                return 0;            memcpy(pBuf, pLoader->m_pBuf + pos, size);            return 1;        }    private:        char* m_pBuf;        size_t m_Len;    };    void RenderPdf(const char* pBuf, size_t len, const Options& options)    {        memset(&platform_callbacks_, '\0', sizeof(platform_callbacks_));        platform_callbacks_.version = 3;        form_callbacks_.version = 1;        form_callbacks_.m_pJsPlatform = &platform_callbacks_;        Loader_ = std::move(std::unique_ptr<TestLoader>(new TestLoader(pBuf, len)));        File_access_ = std::make_unique<FPDF_FILEACCESS>();        memset(File_access_.get(), '\0', sizeof(File_access_.get()));        File_access_->m_FileLen = static_cast<unsigned long>(len);        File_access_->m_GetBlock = TestLoader::GetBlock;        File_access_->m_Param = Loader_.get();        memset(&File_avail_, '\0', sizeof(File_avail_));        File_avail_.version = 1;        File_avail_.IsDataAvail = Is_Data_Avail;        memset(&Hints_, '\0', sizeof(Hints_));        Hints_.version = 1;        int nRet = PDF_DATA_NOTAVAIL;        Pdf_avail_ = FPDFAvail_Create(&File_avail_, File_access_.get());        std::unique_ptr<void, PDFManager::AvailDeleter> scoped_pdf_avail_deleter(Pdf_avail_);        if (FPDFAvail_IsLinearized(Pdf_avail_) == PDF_LINEARIZED)        {            this->PdfDoc_ = FPDFAvail_GetDocument(Pdf_avail_, nullptr);            if (this->PdfDoc_)            {                while (nRet == PDF_DATA_NOTAVAIL)                    nRet = FPDFAvail_IsDocAvail(Pdf_avail_, &Hints_);                if (nRet == PDF_DATA_ERROR)                {                    fprintf(stderr, "Unknown error in checking if doc was available.\n");                    FPDF_CloseDocument(this->PdfDoc_);                    return;                }                nRet = FPDFAvail_IsFormAvail(Pdf_avail_, &Hints_);                if (nRet == PDF_FORM_ERROR || nRet == PDF_FORM_NOTAVAIL)                {                    fprintf(stderr,                        "Error %d was returned in checking if form was available.\n",                        nRet);                    FPDF_CloseDocument(this->PdfDoc_);                    return;                }                this->bIsLinearized_ = true;            }        }        else        {            this->PdfDoc_ = FPDF_LoadCustomDocument(File_access_.get(), nullptr);        }        if (!this->PdfDoc_)        {            unsigned long err = FPDF_GetLastError();            return;        }        (void)FPDF_GetDocPermissions(this->PdfDoc_);        PageCount = FPDF_GetPageCount(this->PdfDoc_);    }public:    PDFManager();    ~PDFManager();    void Init(char *dat, int length);    void Close();    char* GetPdfPage(int page, float& width, float& height, int& size, bool OutBmp = false);//返回长度    void ClosePdfPage(int page);    int PageCount = 0;    int PageCurrent = 0;    int PageBad = 0;private:    FPDF_DOCUMENT PdfDoc_ = nullptr;//文档    //FPDF_FORMHANDLE Form_ = nullptr;    bool bIsLinearized_ = false; //是否线性化    FPDF_FORMFILLINFO_PDFiumTest form_callbacks_;    IPDF_JSPLATFORM platform_callbacks_;    FX_DOWNLOADHINTS Hints_;//    FX_FILEAVAIL File_avail_;    std::unique_ptr<FPDF_FILEACCESS> File_access_;    FPDF_AVAIL Pdf_avail_;    std::unique_ptr<TestLoader> Loader_;    char* File_contents_ = nullptr;    int File_length_ = 0;    std::map<int, char*> Pages_; //保存页面数据};PDFManager::PDFManager(){}PDFManager::~PDFManager(){    for (auto &buffer : Pages_)    {        delete[]buffer.second;    }    Pages_.clear();    this->Close();}void PDFManager::Init(char *dat, int length){    File_contents_ = dat;    File_length_ = length;    Options options;    options.output_format = OutputFormat::OUTPUT_BMP;    if (!File_contents_)        return;    RenderPdf(File_contents_, File_length_, options);}char* PDFManager::GetPdfPage(int page, float& width, float& height, int& size, bool OutBmp){    if (this->bIsLinearized_)    {        this->Close();        return 0;    }    if (page < 0)        return 0;    Options options;    options.currentpage = page;    options.width = width;    options.height = height;    if (!OutBmp)        options.output_format = OUTPUT_STR;    PageCurrent = page;    PageCurrent++;    return RenderPage(this->PdfDoc_, form_callbacks_, width, height, options, size);}void PDFManager::ClosePdfPage(int page){    std::map<int, char*>::iterator itor = Pages_.find(page);    if (itor != Pages_.end())    {        delete[]itor->second;        Pages_.erase(page);    }}void PDFManager::Close(){    if (!this->PdfDoc_)        return;    FPDF_CloseDocument(this->PdfDoc_);}//接口函数std::map<std::string, PDFManager*> g_pdfmanagersmap;bool __stdcall PDFMANAGER_Loadpdf(const char* filename, char* dat, int length){    if (!filename)    {        return false;    }    if (g_pdfmanagersmap.size() == 0)    {        FPDF_LIBRARY_CONFIG config;        config.version = 2;        config.m_pUserFontPaths = nullptr;        config.m_pIsolate = nullptr;        config.m_v8EmbedderSlot = 0;        FPDF_InitLibraryWithConfig(&config);    }    std::string file = filename;    std::map<std::string, PDFManager*>::iterator itor = g_pdfmanagersmap.find(file);    if (itor != g_pdfmanagersmap.end())    {        itor->second->Init(dat, length);    }    else    {        PDFManager* pdfmanager = new PDFManager();        g_pdfmanagersmap.insert(std::make_pair(file, pdfmanager));        pdfmanager->Init(dat, length);    }    return true;}bool __stdcall PDFMANAGER_Closepdf(const char* filename){    if (!filename)    {        return false;    }    std::string file = filename;    std::map<std::string, PDFManager*>::iterator itor = g_pdfmanagersmap.find(file);    if (itor != g_pdfmanagersmap.end())    {        delete itor->second;        g_pdfmanagersmap.erase(file);        if (g_pdfmanagersmap.size() == 0)        {            FPDF_DestroyLibrary();        }    }    return true;}char* __stdcall PDFMANAGER_LoadPage(const char* filename, int page, float& width, float& height, int& size, bool OutBmp){    if (!filename)    {        return nullptr;    }    std::string file = filename;    std::map<std::string, PDFManager*>::iterator itor = g_pdfmanagersmap.find(file);    if (itor != g_pdfmanagersmap.end())    {        return itor->second->GetPdfPage(page, width, height, size, OutBmp);    }    return nullptr;}void __stdcall PDFMANAGER_ClosePage(const char* filename, int page){    if (!filename)    {        return;    }    std::string file = filename;    std::map<std::string, PDFManager*>::iterator itor = g_pdfmanagersmap.find(file);    if (itor != g_pdfmanagersmap.end())    {        itor->second->ClosePdfPage(page);    }}int __stdcall PDFMANAGER_GetPageCount(const char* filename){    if (!filename)    {        return 0;    }    std::string file = filename;    std::map<std::string, PDFManager*>::iterator itor = g_pdfmanagersmap.find(file);    if (itor != g_pdfmanagersmap.end())    {        return itor->second->PageCount;    }    return 0;}int __stdcall PDFMANAGER_GetCurrentPage(const char* filename){    if (!filename)    {        return 0;    }    std::string file = filename;    std::map<std::string, PDFManager*>::iterator itor = g_pdfmanagersmap.find(file);    if (itor != g_pdfmanagersmap.end())    {        return itor->second->PageCurrent;    }    return 0;}

注释说的比较清楚，就不解释了。

3、添加模块文件：

我取名为PdfManager.def，在里面添加如下代码：

LIBRARY "Pdf"EXPORTSPDFMANAGER_Loadpdf @ 1PDFMANAGER_Closepdf @ 2PDFMANAGER_LoadPage @ 3PDFMANAGER_ClosePage @ 4PDFMANAGER_GetPageCount @ 5PDFMANAGER_GetCurrentPage @ 6

即指定要编译成dll的接口函数。

4、编译，最后整理成pdf库：


直接编译release版本就可以了，通用。

三、使用封装好的pdf动态库：

1、在vs中使用：

1.1 先新建测试项目
1.2 添加pdf库
1.2 添加代码：
main.cpp：

#include <iostream>#include <fstream>#include "PdfManager.h"#include <memory>#include <windows.h>char* GetFileContents(const char* filename, size_t *size){    std::fstream instream;    instream.open(filename, std::ios::_Nocreate | std::ios::binary);    if (!instream.is_open())    {        std::printf("open file Failed!\n");        std::printf("%s\n", filename);        instream.close();        return nullptr;    }    instream.seekg(0, std::ios::end);    *size = instream.tellg();    instream.seekg(0, std::ios::beg);    char *buffer = new char[*size];    instream.read(buffer, *size);    instream.close();    return buffer;}int main(){    char* name = "test.pdf";    size_t length;    std::unique_ptr<char>  filecontents(GetFileContents(name, &length));    PDFMANAGER_Loadpdf(name, filecontents.get(), length);    int counts = PDFMANAGER_GetPageCount(name);    for (int i = 0; i < counts; ++i)    {        if (GetAsyncKeyState(VK_F2) & 0x8000)            break;        float width, height = 0;        int length = 0;        PDFMANAGER_LoadPage(name, i, width, height, length, true);        PDFMANAGER_ClosePage(name, i);    }    PDFMANAGER_Closepdf(name);    system("pause");    return 0;}

结果如图（数字.bmp是渲染出来的每一页，我只渲染完三页就关了）：

2、在qt中使用：

2.1新建qt项目
2.2 导入pdf动态库
2.3关键代码（ui逻辑代码就不贴了，其实就是主要讲怎么用，怎么渲染）：

PDFForm::PDFForm(const char *filename, QByteArray &bytearray, QWidget *parent) :    QWidget(parent),    ui(new Ui::PDFForm){    ui->setupUi(this);    FileLength_ = bytearray.length();    File_ = new char[FileLength_];    std::memcpy(File_, bytearray.toStdString().c_str(), FileLength_);    FileName_ = filename;    Picture_ = new PictureBox();    Picture_->setMode(PictureBox::PB_MODE::FIX_SIZE_CENTRED );    this->ui->verticalLayout_2->addWidget(Picture_);}void PDFForm::InitFile(){    if(HaveLoadPdf_)        return;    int length = (int)FileLength_;    PDFMANAGER_Loadpdf(FileName_.c_str(), File_, length);    HaveLoadPdf_ = true;    PageCount_ = PDFMANAGER_GetPageCount(FileName_.c_str());    this->LoadPage(0);}void PDFForm::LoadPage(int page){    if(!HaveLoadPdf_)        return;    int length = 0;    QRect rect = this->ui->verticalLayout_2->geometry();    float width = rect.width();    float height = rect.height();    char* Buffer = PDFMANAGER_LoadPage(FileName_.c_str(),page, width, height, length, false);    QImage image((uchar*)Buffer, width, height, QImage::Format_RGBA8888);    this->Picture_->setImage(image);    PDFMANAGER_ClosePage(FileName_.c_str(),page);//释放页面内存    UpdateLabelPage();}

效果如下图：

到这里就完成了需要在qt中显示或打开pdf的需求，还做了适配，可以直接拉伸缩小，而且最主要的是，因为其本质是位图，放大缩小时重新loadpage可以实现分辨率也不断放大缩小。

四、结语：

1、本系列到此结束，其实还有些东西，比如在qt里做显示适配，例如上面的Picture_对象就是自定义的一个image类，在界面上显示时方便居中，要写的话还可以写第五篇，但是我暂时没空，就打住了，以后会不会补需要再看看。

2、本次研究说实话让我提升很多，很多是思维和经验上的改变，独立能力稍微有点加强，希望能早日成为大牛。

17.05.19更新：
代码地址：
传送门

17.07.27更新：
大家不用留邮箱了，我不是经常上这个帐号，下载连接也贴了，也不花积分，直接下载就好了（ps：我自己下了，也叫别人下了，文件没问题，下载下来有问题重新试试，csdn是经常抽风，网络不是很稳定）

17.08.09更新：
鉴于很多人问我要在QT中打开的demo，现在补上（如果觉得不错，不妨点个顶或者关注，你的鼓励是对我最大的支持）：
传送门
另外 需要1积分，不知道为啥，现在csdn资源最少1积分，包括我以前的0分资源全部自动调整为1分，特此说明。