c++ 屏幕截图指定窗口句柄后台截图返回位图句柄

/根据窗口句柄后台截图保存成BMP位图文件并且显示到picture 控件上
void GetScreenBmp(HWND hwnd, int left, int top, int width, int height, CHAR* path)
{

    HDC pDC;// 源DC
    //判断是不是窗口句柄如果是的话不能使用GetDC来获取DC 不然截图会是黑屏
    if (hwnd==::GetDesktopWindow())
    {
        pDC = CreateDCA("DISPLAY", NULL, NULL, NULL);
    }
    else
    {
        pDC = ::GetDC(hwnd);//获取屏幕DC(0为全屏，句柄则为窗口)
    }
    int BitPerPixel = ::GetDeviceCaps(pDC, BITSPIXEL);//获得颜色模式
    if (width == 0 && height == 0)//默认宽度和高度为全屏
    {
        width = ::GetDeviceCaps(pDC, HORZRES); //设置图像宽度全屏
        height = ::GetDeviceCaps(pDC, VERTRES); //设置图像高度全屏
    }
    HDC memDC;//内存DC
    memDC = ::CreateCompatibleDC(pDC);
    HBITMAP memBitmap, oldmemBitmap;//建立和屏幕兼容的bitmap
    memBitmap = ::CreateCompatibleBitmap(pDC, width, height);
    oldmemBitmap = (HBITMAP)::SelectObject(memDC, memBitmap);//将memBitmap选入内存DC
    if (hwnd==::GetDesktopWindow())
    {
        BitBlt(memDC,0, 0, width, height, pDC, left, top, SRCCOPY);//图像宽度高度和截取位置
    }
    else
    {
        bool bret = ::PrintWindow(hwnd, memDC, PW_CLIENTONLY);
        if (!bret)
        {
            BitBlt(memDC, 0, 0, width, height, pDC, left, top, SRCCOPY);//图像宽度高度和截取位置
        }
    }
    //以下代码保存memDC中的位图到文件
    BITMAP bmp;
    ::GetObject(memBitmap, sizeof(BITMAP), &bmp);;//获得位图信息
    FILE *fp;
    fopen_s(&fp, path, "w+b");//图片保存路径和方式

    BITMAPINFOHEADER bih = { 0 };//位图信息头
    bih.biBitCount = bmp.bmBitsPixel;//每个像素字节大小
    bih.biCompression = BI_RGB;
    bih.biHeight = bmp.bmHeight;//高度
    bih.biPlanes = 1;
    bih.biSize = sizeof(BITMAPINFOHEADER);
    bih.biSizeImage = bmp.bmWidthBytes * bmp.bmHeight;//图像数据大小
    bih.biWidth = bmp.bmWidth;//宽度

    BITMAPFILEHEADER bfh = { 0 };//位图文件头
    bfh.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);//到位图数据的偏移量
    bfh.bfSize = bfh.bfOffBits + bmp.bmWidthBytes * bmp.bmHeight;//文件总的大小
    bfh.bfType = (WORD)0x4d42;

    fwrite(&bfh, 1, sizeof(BITMAPFILEHEADER), fp);//写入位图文件头
    fwrite(&bih, 1, sizeof(BITMAPINFOHEADER), fp);//写入位图信息头
    byte * p = new byte[bmp.bmWidthBytes * bmp.bmHeight];//申请内存保存位图数据
    GetDIBits(memDC, (HBITMAP)memBitmap, 0, height, p,
        (LPBITMAPINFO)&bih, DIB_RGB_COLORS);//获取位图数据
    fwrite(p, 1, bmp.bmWidthBytes * bmp.bmHeight, fp);//写入位图数据
    delete[] p;
    fclose(fp);
    HWND sBitHwnd = GetDlgItem(g_Hwnd, IDC_STATIC_IMG);
    /*返回内存中的位图句柄 还原原来的内存DC位图句柄 不能直接用 memBitmap我测试好像是不行不知道为什么*/
    HBITMAP oleImage = (HBITMAP)::SelectObject(memDC, oldmemBitmap);
    oleImage = (HBITMAP)SendMessage(sBitHwnd, STM_SETIMAGE, IMAGE_BITMAP, (LPARAM)oleImage);
#if 0
    /*这种方法也能把位图显示到picture 控件上*/
    HDC bitDc = NULL;
    bitDc = ::GetDC(sBitHwnd);
    BitBlt(bitDc, 0, 0, bmp.bmWidth, bmp.bmHeight, memDC, 0, 0, SRCCOPY); //内存DC映射到屏幕DC
     ReleaseDC(sBitHwnd, bitDc);
    /*如果需要把位图转换*/
    /*
    CImage image;
    image.Create(nWidth, nHeight, nBitPerPixel);
    BitBlt(image.GetDC(), 0, 0, nWidth, nHeight, hdcSrc, 0, 0, SRCCOPY);
    ::ReleaseDC(NULL, hdcSrc);
    image.ReleaseDC();
    image.Save(path, Gdiplus::ImageFormatPNG);//ImageFormatJPEG
    */
#endif
      DeleteObject(memBitmap);
    DeleteObject(oleImage);
      DeleteDC(memDC);
      ReleaseDC(hwnd,pDC);

}