To display a huge image... how to do it?

Yes, it appears that you can use FileMapping.  It  involves using CreateFileMapping and MapViewOfFile and there is a trick having to do with forcing the dibsection data to be aligned on a DWORD boundary.  

Alas, I can't find a pat answer for you.  Perhaps someone else can locate some sample code.  If you up the points, I'll take a whack at it.

-- Dan

Sure, I am waiting for your further help. :)

OK Here's a FIRST DRAFT -- it is for testing purposes ONLY:

THere is a big problem that I'm not certain how to attack:  The image area (the bits) do not normally end up on a DWORD-aligned boundary -- and that is a requirement for using the CreateDIBSection API which seems to be the logical way to attack this problem.

As a proof-of-concept, I just added an offset so that the bits are aligned (I had to make the images shorter to avoid a related error).  The result is that I can access the data, but it is color-shifted (RGB RGB RGB is interpetted as GBR GBR GBR).  

Note: I woked on a 2MB file (the largest I could find!) and the girl looks like one of those Intel 'bluemen' lol.

This code shows how to do the file mapping and so forth and actually displays a specified portion of a large bitmap.  I'd like you to try it and single-step through the code. and examine all variables ate each step.  Perhaps you can see something different.

Do you have access to the program that creates these whopping GB+ files?  Is there anything on on earth that can read them?  If you have access to the program, you could add a couple of filler bytes ate one place in the file and the work would be done.

Otherwise, I'll need to either shift the entire file forward by 2 bytes (probably not feasible) or do manual operations of copying subsets of the data into a temporary buffer.  That much coding will take me hours...

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void GetLastErrorStr( CString& sDest );
HBITMAP GetImgSubSet( HBITMAP hbmSrc, RECT* prcSrc, BITMAPINFO* pBMI, void* pBits ) ;

void CD06Dlg::OnButton1()
{
      HANDLE            hFile;
      HANDLE            hFileMapping;
      BITMAPFILEHEADER* pBMFH;
      BITMAPINFO*       pBMI;    // bfOffBits is not divisible by 4.
      BITMAPINFOHEADER* pBMIH;

      hFile=        CreateFile( "C:\\temp\\large.bmp",GENERIC_READ|GENERIC_WRITE,0,0,OPEN_EXISTING,0,NULL);
      hFileMapping= CreateFileMapping( hFile,NULL,PAGE_READWRITE,0,0,0 );

      CString s;
      GetLastErrorStr( s );

      pBMFH= (BITMAPFILEHEADER*)MapViewOfFile( hFileMapping,FILE_MAP_ALL_ACCESS,0,0,0);  // entire file
      pBMI=  (BITMAPINFO*)     (pBMFH+1);

      GetLastErrorStr( s );

      DWORD dwOffset= pBMFH->bfOffBits;

      if ( (dwOffset & 3 ) != 0 ) {
            MessageBox("Problem mapping: bit data not dword-aligned!" );
            int nAdjust= dwOffset % 4;  // usually 2
            dwOffset += nAdjust;
            pBMI->bmiHeader.biHeight--; // discared last scanline for this test
      }

      HDC dc= CreateCompatibleDC(NULL);

      void* pBits=    0;

      HBITMAP hBmp= CreateDIBSection(dc,pBMI,DIB_RGB_COLORS, &pBits, hFileMapping, dwOffset );
      if (hBmp == 0 ) {
            MessageBox("CreateDIBSection failed!" );
      }
      GetLastErrorStr( s );  // useless

      pBMIH= (BITMAPINFOHEADER*)pBMI;
      int nWidth= pBMIH->biWidth;
      int nHigh=  pBMIH->biHeight;

      RECT rc= {100,100,400,400 };
      static HBITMAP hBmpNew= GetImgSubSet( hBmp, &rc, pBMI, pBits) ;

      m_ctlBmpShow.SetBitmap( hBmpNew );

      DeleteDC(dc);
      CloseHandle( hFile ); // or just exit the testing program
}

HBITMAP GetImgSubSet( HBITMAP hbmSrc, RECT* prcSrc, BITMAPINFO* zpBMI, void* pBits )
{
      HWND hWnd= AfxGetMainWnd()->m_hWnd;
      int nHigh= prcSrc->bottom - prcSrc->top;
      int nWide= prcSrc->right  - prcSrc->left;

      //---------------------------- create the destination bitmap
      HDC hDCMem= ::CreateCompatibleDC( NULL );
      HBITMAP hBmp= NULL;
      HDC hDC= ::GetDC( hWnd );
      hBmp= CreateCompatibleBitmap( hDC, nWide, nHigh );
      ::ReleaseDC( hWnd, hDC );

      HGDIOBJ hOldBmp= SelectObject( hDCMem, hBmp );

      BITMAP rBmp;
      GetObject( hbmSrc, sizeof(BITMAP), &rBmp );

      DIBSECTION rDS;
      GetObject( hbmSrc, sizeof(DIBSECTION), &rDS );


      BITMAPINFO* pBMI= (BITMAPINFO*)&rDS.dsBmih;
      
      int nScansCopied=
            StretchDIBits( hDCMem,
            0,0,                       // dest location
            nWide, nHigh,              // dest size
            prcSrc->left, prcSrc->top, // src Location
            nWide, nHigh,              // src size
            pBits,
            pBMI,
            DIB_RGB_COLORS,
            SRCCOPY
      );

      ::SelectObject( hDCMem, hOldBmp );
      ::DeleteObject( hDCMem );

      return( hBmp );
}

Hello Dan, thanks a lot for your help. I tried your code, some of which is ingenious, but it failed at "MapViewOfFile" cuz I used a whopping image file (over 900M) which made it memory insufficient. How could I get it over?

On second thought, this may not work.  I can't find a single reference about how to handle this.

How are most of these bitmaps laid out?  Very wide and not too tall?   Is there someplace I could download one for testing?

If the monster BMP file is certain to be a DIB with standard 24-bit color, it is possible to just open the file and read in carefully-selected chunks of it to form a DIBSection in RAM.  From that, I could extract a specified rectangle and return an HBITMAP of it.

If you bump the points again, I'll take a crack at that.

-- Dan

Okay, I think it's tough while interesting, it's worth a study :)

Dan, thank you for your hard working, I appreciate it. I think your answer meet my requirement basically, I will improve it by myself. Thanks. Chances are I will have more questions in the future, please give me your Email address in order to let you know that I have new questions about a display of big image. :) Thanks again!

I worked many hours to help you for free.  I solved a problem that no other expert would touch.  A problem that is considered impossible to solve.  Then you give me a B!
 
>>please give me your Email address in order to let you know that I have new questions

This has made me laugh quite hard.  My side hurts.

-- Dan

I am so sorry, Dan. I don't know much of this website and I must give you an "A" if I can choose again.

I will take my words back. Sorry