HBITMAP CreateBitmapMask(HBITMAP hbmColour, COLORREF crTransparent)
{
    HDC hdcMem, hdcMem2;
    HBITMAP hbmMask;
    BITMAP bm;

    // Create monochrome (1 bit) mask bitmap.  

    GetObject(hbmColour, sizeof(BITMAP), &bm);
    hbmMask = CreateBitmap(bm.bmWidth, bm.bmHeight, 1, 1, NULL);

    // Get some HDCs that are compatible with the display driver

    hdcMem = CreateCompatibleDC(0);
    hdcMem2 = CreateCompatibleDC(0);

    SelectBitmap(hdcMem, hbmColour);
    SelectBitmap(hdcMem2, hbmMask);

    // Set the background colour of the colour image to the colour
    // you want to be transparent.
    SetBkColor(hdcMem, crTransparent);

    // Copy the bits from the colour image to the B+W mask... everything
    // with the background colour ends up white while everythig else ends up
    // black...Just what we wanted.

    BitBlt(hdcMem2, 0, 0, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);

    // Take our new mask and use it to turn the transparent colour in our
    // original colour image to black so the transparency effect will
    // work right.
    BitBlt(hdcMem, 0, 0, bm.bmWidth, bm.bmHeight, hdcMem2, 0, 0,SRCINVERT);
    DeleteDC(hdcMem);
    DeleteDC(hdcMem2);

    return hbmMask;
}


    

proc CreateBitmapMask,hbmColour,crTransparent
    invoke GetObject,hbmColour,38h,bmp1H
    invoke CreateBitmap,49, 48,1,1, NULL
    mov    [hbmMask],eax
    invoke CreateCompatibleDC,dcMemH
    invoke CreateCompatibleDC,dcMem2H
    invoke SelectBitmap,dcMemH,hbmColour
    invoke SelectBitmap,dcMem2H,hbmMask
    invoke SetBkColor,dcMemH,00000000h
    invoke BitBlt,dcMem2H, 0, 0, 49, 44, dcMemH, 0, 0, SRCCOPY
    invoke BitBlt,dcMemH, 0, 0, 49, 44, dcMem2H, 0, 0,SRCINVERT
    invoke DeleteDC,dcMemH
    invoke DeleteDC,dcMem2H
    mov    eax,hbmMask
    ret
endp