How to create a new HBITMAP(DIB) from an existing HBITMAP(CreateCompatibleBitmap)?

Question

I created a bitmap by CreateCompatibleBitmap() for capturing the screen. Then I want to create a new DIB (in memory) from this bitmap.

The code should look be:

HBITMAP ConvertToDIB(HBITMAP ddb)
{ ... }

I already have some code to write a bitmap into a file. However, I want a HBITMAP in memory.

//---------------------------------------------------------------------------
void WriteBitmapToFile(HBITMAP bitmap, wchar_t* filename, HDC hDC)
{
    BITMAP bmp;
    PBITMAPINFO pbmi;
    WORD cClrBits;
    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;

    // create the bitmapinfo header information
    if (!::GetObjectW(bitmap, sizeof(BITMAP), &bmp))
    {
        return;
    }

    // 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.
    if (cClrBits != 24)
    pbmi = (PBITMAPINFO) LocalAlloc(LPTR,
    sizeof(BITMAPINFOHEADER) + sizeof(RGBQUAD) * (1<< cClrBits));
    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;

    // now open file and save the data
    pbih = (PBITMAPINFOHEADER) pbmi;
    lpBits = (LPBYTE) GlobalAlloc(GMEM_FIXED, pbih->biSizeImage);

    if (!lpBits)
    {
        return;
    }

    // Retrieve the color table (RGBQUAD array) and the bits
    if (!GetDIBits(hDC, HBITMAP(bitmap), 0, (WORD) pbih->biHeight, lpBits, pbmi,
    DIB_RGB_COLORS))
    {
        return;
    }

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

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


    // 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;
    }

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

    // Free memory.
    GlobalFree((HGLOBAL)lpBits);
}

Best regards, Zach

Answer 1

If you simply want to convert HBITMAP to DIB (device independent bitmap), there's a Win32 GDI function called GetDIBits.

int GetDIBits(
  __in     HDC hdc,
  __in     HBITMAP hbmp,
  __in     UINT uStartScan,
  __in     UINT cScanLines,
  __out    LPVOID lpvBits,
  __inout  LPBITMAPINFO lpbi,
  __in     UINT uUsage
);

Here's the link to GetDIBits function on MSDN:
http://msdn.microsoft.com/en-us/library/dd144879(v=vs.85).aspx

Note that you have to allocate memory for the lpvBits before calling GetDIBits. But how much memory should be allocated is another question here:
How much memory should be allocated for the DIB data received from HBITMAP using GetDIBits function?