CaptureScreenToBitmap

// Takes a screenshot and save it to a bitmap image.
//
// Sources:
// 1) MSDN index["bitmaps [Win32]", "code examples"]->"Capturing an image"
// 2) MSDN index["bitmaps [Win32]", "code examples"]->"Storing an image"
//
// Web: http://unclassified.software/source/capturescreentobitmap
//
int CaptureBMP(LPCTSTR szFile)
{
    // Source[1]
    HDC hdcScr, hdcMem;
    HBITMAP hbmScr;
    BITMAP bmp;
    int iXRes, iYRes;

    // Create a normal DC and a memory DC for the entire screen. The
    // normal DC provides a "snapshot" of the screen contents. The
    // memory DC keeps a copy of this "snapshot" in the associated
    // bitmap.
    hdcScr = CreateDC("DISPLAY", NULL, NULL, NULL);
    hdcMem = CreateCompatibleDC(hdcScr);

    iXRes = GetDeviceCaps(hdcScr, HORZRES);
    iYRes = GetDeviceCaps(hdcScr, VERTRES);

    // Create a compatible bitmap for hdcScreen.
    hbmScr = CreateCompatibleBitmap(hdcScr, iXRes, iYRes);
    if (hbmScr == 0) return 0;

    // Select the bitmaps into the compatible DC.
    if (!SelectObject(hdcMem, hbmScr)) return 0;

    // Copy color data for the entire display into a
    // bitmap that is selected into a compatible DC.
    if (!StretchBlt(hdcMem,
        0, 0, iXRes, iYRes,
        hdcScr,
        0, 0, iXRes, iYRes,
        SRCCOPY)) return 0;

    // Source[2]
    PBITMAPINFO pbmi;
    WORD cClrBits;

    // Retrieve the bitmap's color format, width, and height.
    if (!GetObject(hbmScr, sizeof(BITMAP), (LPSTR) &bmp)) return 0;

    // Convert the color format to a count of bits.
    cClrBits = (WORD) (bmp.bmPlanes * bmp.bmBitsPixel);
    if (cClrBits == 1)
        cClrBits = 1;
    else if (cClrBits <= 4)
        cClrBits = 4;
    else if (cClrBits <= 8)
        cClrBits = 8;
    else if (cClrBits <= 16)
        cClrBits = 16;
    else if (cClrBits <= 24)
        cClrBits = 24;
    else cClrBits = 32;

    // Allocate memory for the BITMAPINFO structure. (This structure
    // contains a BITMAPINFOHEADER structure and an array of RGBQUAD
    // data structures.)
    if (cClrBits != 24)
        pbmi = (PBITMAPINFO) LocalAlloc(LPTR,
                sizeof(BITMAPINFOHEADER) +
                sizeof(RGBQUAD) * (1 << cClrBits));

    // There is no RGBQUAD array for the 24-bit-per-pixel format.
    else
        pbmi = (PBITMAPINFO) LocalAlloc(LPTR,
                sizeof(BITMAPINFOHEADER));

    // Initialize the fields in the BITMAPINFO structure.
    pbmi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    pbmi->bmiHeader.biWidth = bmp.bmWidth;
    pbmi->bmiHeader.biHeight = bmp.bmHeight;
    pbmi->bmiHeader.biPlanes = bmp.bmPlanes;
    pbmi->bmiHeader.biBitCount = bmp.bmBitsPixel;
    if (cClrBits < 24)
        pbmi->bmiHeader.biClrUsed = (1 << cClrBits);

    // If the bitmap is not compressed, set the BI_RGB flag.
    pbmi->bmiHeader.biCompression = BI_RGB;

    // Compute the number of bytes in the array of color
    // indices and store the result in biSizeImage.
    pbmi->bmiHeader.biSizeImage = (pbmi->bmiHeader.biWidth + 7) / 8
                                    * pbmi->bmiHeader.biHeight * cClrBits;

    // Set biClrImportant to 0, indicating that all of the
    // device colors are important.
    pbmi->bmiHeader.biClrImportant = 0;

    HANDLE hf;                  // file handle
    BITMAPFILEHEADER hdr;       // bitmap file-header
    PBITMAPINFOHEADER pbih;     // bitmap info-header
    LPBYTE lpBits;              // memory pointer
    DWORD dwTotal;              // total count of bytes
    DWORD cb;                   // incremental count of bytes
    BYTE *hp;                   // byte pointer
    DWORD dwTmp;

    pbih = (PBITMAPINFOHEADER) pbmi;
    lpBits = (LPBYTE) GlobalAlloc(GMEM_FIXED, pbih->biSizeImage);

    if (!lpBits) return 0;

    // Retrieve the color table (RGBQUAD array) and the bits
    // (array of palette indices) from the DIB.
    if (!GetDIBits(hdcMem, hbmScr, 0, (WORD) pbih->biHeight,
        lpBits, pbmi, DIB_RGB_COLORS)) return 0;

    // Create the .BMP file.
    hf = CreateFile(szFile,
                    GENERIC_READ | GENERIC_WRITE,
                    (DWORD) 0,
                    NULL,
                    CREATE_ALWAYS,
                    FILE_ATTRIBUTE_NORMAL,
                    (HANDLE) NULL);
    if (hf == INVALID_HANDLE_VALUE) return 0;

    hdr.bfType = 0x4d42;        // 0x42 = "B" 0x4d = "M"

    // Compute the size of the entire file.
    hdr.bfSize = (DWORD) (sizeof(BITMAPFILEHEADER) +
                 pbih->biSize + pbih->biClrUsed *
                 sizeof(RGBQUAD) + pbih->biSizeImage);
    hdr.bfReserved1 = 0;
    hdr.bfReserved2 = 0;

    // Compute the offset to the array of color indices.
    hdr.bfOffBits = (DWORD) sizeof(BITMAPFILEHEADER) +
                    pbih->biSize + pbih->biClrUsed *
                    sizeof (RGBQUAD);

    // Copy the BITMAPFILEHEADER into the .BMP file.
    if (!WriteFile(hf, (LPVOID) &hdr, sizeof(BITMAPFILEHEADER),
        (LPDWORD) &dwTmp, NULL)) return 0;

    // Copy the BITMAPINFOHEADER and RGBQUAD array into the file.
    if (!WriteFile(hf, (LPVOID) pbih, sizeof(BITMAPINFOHEADER)
                + pbih->biClrUsed * sizeof (RGBQUAD),
                (LPDWORD) &dwTmp, NULL))
        return 0;

    // Copy the array of color indices into the .BMP file.
    dwTotal = cb = pbih->biSizeImage;
    hp = lpBits;
    if (!WriteFile(hf, (LPSTR) hp, (int) cb, (LPDWORD) &dwTmp, NULL)) return 0;

    // Close the .BMP file.
    if (!CloseHandle(hf)) return 0;

    // Free memory.
    GlobalFree((HGLOBAL)lpBits);
    ReleaseDC(0, hdcScr);
    ReleaseDC(0, hdcMem);

    return 1;
}