C++保存HBITMAP为位图文件的实现方法

#pragma once
 
#include <windows.h>
#include <string>
using namespace std;
 
class imagehelper
{
public:
    static bool savebitmaptofile(hbitmap bitmap, const string& filename); //保存位图到文件
 
private:
    static word getbitmapbitcount(); //计算位图文件每个像素所占字节数
    static void processpalette(hbitmap hbitmap, const bitmap& bitmap,
        dword palettesize, lpbitmapinfoheader lpbmpinfoheader); //处理调色板
};

#include "imagehelper.h"
#include <shlwapi.h>
 
 
bool imagehelper::savebitmaptofile(hbitmap hbitmap, const string& filename)
{
    //1. 创建位图文件
    const auto file = createfilea(filename.c_str(), generic_write,
        0, nullptr, create_always,
        file_attribute_normal | file_flag_sequential_scan,
        nullptr);
    if (file == invalid_handle_value)
    {
        return false;
    }
 
    //2. 计算位图文件每个像素所占字节数
    const auto bitcount = getbitmapbitcount();
 
    //3. 获取位图结构
    bitmap bitmap;
    ::getobject(hbitmap, sizeof(bitmap), reinterpret_cast<lpstr>(&bitmap));
 
    //位图中像素字节大小(32字节对齐)
    const dword bmbitssize = ((bitmap.bmwidth * bitcount + 31) / 32) * 4 * bitmap.bmheight;
 
    //调色板大小
    const dword palettesize = 0;
 
    //4. 构造位图信息头
    bitmapinfoheader  bmpinfoheader; //位图信息头结构
    bmpinfoheader.bisize = sizeof(bitmapinfoheader);
    bmpinfoheader.biwidth = bitmap.bmwidth;
    bmpinfoheader.biheight = bitmap.bmheight;
    bmpinfoheader.biplanes = 1;
    bmpinfoheader.bibitcount = bitcount;
    bmpinfoheader.bicompression = bi_rgb;
    bmpinfoheader.bisizeimage = 0;
    bmpinfoheader.bixpelspermeter = 0;
    bmpinfoheader.biypelspermeter = 0;
    bmpinfoheader.biclrimportant = 0;
    bmpinfoheader.biclrused = 0;
 
    //5. 构造位图文件头
    bitmapfileheader bmpfileheader;
    bmpfileheader.bftype = 0x4d42; //"bm"
    //位图文件大小
    const dword dibsize = sizeof(bitmapfileheader) + sizeof(bitmapinfoheader) + palettesize + bmbitssize;
    bmpfileheader.bfsize = dibsize;
    bmpfileheader.bfreserved1 = 0;
    bmpfileheader.bfreserved2 = 0;
    bmpfileheader.bfoffbits = static_cast<dword>(sizeof(bitmapfileheader))
        + static_cast<dword>(sizeof(bitmapinfoheader)) + palettesize;
 
    //6. 为位图内容分配内存 
    const auto dib = globalalloc(ghnd, bmbitssize + palettesize + sizeof(bitmapinfoheader)); //内存句柄
    const auto lpbmpinfoheader = static_cast<lpbitmapinfoheader>(globallock(dib)); //指向位图信息头结构
    *lpbmpinfoheader = bmpinfoheader;
 
    //7. 处理调色板
    processpalette(hbitmap, bitmap, palettesize, lpbmpinfoheader);
 
    //8. 写入文件
    dword written = 0; //写入文件字节数   
    writefile(file, reinterpret_cast<lpstr>(&bmpfileheader), sizeof(bitmapfileheader),
        &written, nullptr); //写入位图文件头
    writefile(file, reinterpret_cast<lpstr>(lpbmpinfoheader), dibsize,
        &written, nullptr); //写入位图文件其余内容
 
    //9. 清理资源
    globalunlock(dib);
    globalfree(dib);
    closehandle(file);
 
    return true;
}
 
//计算位图文件每个像素所占字节数
word imagehelper::getbitmapbitcount()
{
    const auto dc = ::createdca("display", nullptr, nullptr, nullptr);
    //当前分辨率下每像素所占字节数
    const auto bits = ::getdevicecaps(dc, bitspixel) * getdevicecaps(dc, planes);
    ::deletedc(dc);
 
    //位图中每像素所占字节数
    word bitcount;
    if (bits <= 1)
        bitcount = 1;
    else if (bits <= 4)
        bitcount = 4;
    else if (bits <= 8)
        bitcount = 8;
    else
        bitcount = 24;
 
    return bitcount;
}
 
//处理调色板
void imagehelper::processpalette(hbitmap hbitmap, const bitmap& bitmap,
    dword palettesize, lpbitmapinfoheader lpbmpinfoheader)
{
    handle oldpalette = nullptr;
    hdc dc = nullptr;
    const auto palette = getstockobject(default_palette);
    if (palette != nullptr)
    {
        dc = ::getdc(nullptr);
        oldpalette = ::selectpalette(dc, static_cast<hpalette>(palette), false);
        ::realizepalette(dc); //实现设备调色板
    }
 
    //获取该调色板下新的像素值
    getdibits(dc, hbitmap, 0, static_cast<uint>(bitmap.bmheight),
        reinterpret_cast<lpstr>(lpbmpinfoheader) + sizeof(bitmapinfoheader) + palettesize,
        reinterpret_cast<bitmapinfo*>(lpbmpinfoheader), dib_rgb_colors);
 
    //恢复调色板
    if (oldpalette != nullptr)
    {
        ::selectpalette(dc, static_cast<hpalette>(oldpalette), true);
        ::realizepalette(dc);
        ::releasedc(nullptr, dc);
    }
}