How to snap an OpenGL client and send it to the clipboard

This article demonstrates how to snap an OpenGL client and send it to ClipBoard.
We suppose your screen configuration is set to true color.
We could send the same buffer in a .bmp file in a few lines too....

// Snap OpenGL client and send it to ClipBoard
// so that you can insert it in your favorite
// image editor, Powerpoint, etc...
// Replace CRenderView by your own CView-derived class
void CRenderView::SnapClient()
{
 BeginWaitCursor();

 // Get client geometry
 CRect rect;
 GetClientRect(&rect);
 CSize size(rect.Width(),rect.Height());
 TRACE("  client zone : (%d;%d)\n",size.cx,size.cy);
 // Lines have to be 32 bytes aligned, suppose 24 bits per pixel
 // I just cropped it
 size.cx -= size.cx % 4;
 TRACE("  final client zone : (%d;%d)\n",size.cx,size.cy);

 // Create a bitmap and select it in the device context
 // Note that this will never be used ;-) but no matter
 CBitmap bitmap;
 CDC *pDC = GetDC();
 CDC MemDC;
 ASSERT(MemDC.CreateCompatibleDC(NULL));
 ASSERT(bitmap.CreateCompatibleBitmap(pDC,size.cx,size.cy));
 MemDC.SelectObject(&bitmap);

 // Alloc pixel bytes
 int NbBytes = 3 * size.cx * size.cy;
 unsigned char *pPixelData = new unsigned char[NbBytes];

 // Copy from OpenGL
 ::glReadPixels(0,0,size.cx,size.cy,GL_RGB,GL_UNSIGNED_BYTE,pPixelData);

 // Fill header
 BITMAPINFOHEADER header;
 header.biWidth = size.cx;
 header.biHeight = size.cy;
 header.biSizeImage = NbBytes;
 header.biSize = 40;
 header.biPlanes = 1;
 header.biBitCount =  3 * 8; // RGB
 header.biCompression = 0;
 header.biXPelsPerMeter = 0;
 header.biYPelsPerMeter = 0;
 header.biClrUsed = 0;
 header.biClrImportant = 0;

 // Generate handle
 HANDLE handle = (HANDLE)::GlobalAlloc (GHND,sizeof(BITMAPINFOHEADER) + NbBytes);
 if(handle != NULL)
 {
  // Lock handle
  char *pData = (char *) ::GlobalLock((HGLOBAL)handle);
  // Copy header and data
  memcpy(pData,&header,sizeof(BITMAPINFOHEADER));
  memcpy(pData+sizeof(BITMAPINFOHEADER),pPixelData,NbBytes);
  // Unlock
  ::GlobalUnlock((HGLOBAL)handle);

  // Push DIB in clipboard
  OpenClipboard();
  EmptyClipboard();
  SetClipboardData(CF_DIB,handle);
  CloseClipboard();
 }

 // Cleanup
 MemDC.DeleteDC();
 bitmap.DeleteObject();
 delete [] pPixelData;

 EndWaitCursor();
}
 
 



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  • Gray box, still.

    Posted by Legacy on 10/20/2003 12:00am

    Originally posted by: Russ Lewis

    Here's my copy of this solution, however I still
    get the Gray box on the paste operation to mspaint. Any ideas/suggestions?

    wglMakeCurrent() returns FALSE but the extended error
    message returns "The operation completed successfully."

    according to Platform SDK: OpenGL --
    When the wglMakeCurrent function succeeds, the return value is TRUE; otherwise the return value is FALSE.

    what's up with this?

    thanks for any help.

    void CSimpleSDIGLView::SnapClient()
    {
    BeginWaitCursor();

    // Get client geometry
    CRect rect;
    GetClientRect(&rect);
    CSize size(rect.Width(),rect.Height());
    TRACE(" client zone : (%d;%d)\n",size.cx,size.cy);
    // Lines have to be 32 bytes aligned, suppose 24 bits per pixel
    // I just cropped it
    size.cx -= size.cx % 4;
    TRACE(" final client zone : (%d;%d)\n",size.cx,size.cy);

    // Create a bitmap and select it in the device context
    // Note that this will never be used ;-) but no matter
    CBitmap bitmap;
    CDC *pDC = GetDC();
    CDC MemDC;
    VERIFY(MemDC.CreateCompatibleDC(NULL));
    VERIFY(bitmap.CreateCompatibleBitmap(pDC,size.cx,size.cy));
    MemDC.SelectObject(&bitmap);

    // Alloc pixel bytes
    int NbBytes = 3 * size.cx * size.cy;
    unsigned char *pPixelData = new unsigned char[NbBytes];
    if( FALSE == wglMakeCurrent(m_OpenGLCtrl.getDC(), m_OpenGLCtrl.getRC()))
    {
    AfxMessageBox("FALSE from wglMakeCurrent");
    LPVOID lpMsgBuf;
    FormatMessage(
    FORMAT_MESSAGE_ALLOCATE_BUFFER |
    FORMAT_MESSAGE_FROM_SYSTEM |
    FORMAT_MESSAGE_IGNORE_INSERTS,
    NULL,
    GetLastError(),
    MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
    (LPTSTR) &lpMsgBuf,
    0,
    NULL
    );
    // Process any inserts in lpMsgBuf.
    // ...
    // Display the string.
    AfxMessageBox( (LPCTSTR)lpMsgBuf);
    // Free the buffer.
    LocalFree( lpMsgBuf );
    }


    // Copy from OpenGL
    ::glReadPixels(0,0,size.cx,size.cy,GL_BGR_EXT,GL_UNSIGNED_BYTE,pPixelData);

    // Fill header
    BITMAPINFOHEADER header;
    header.biWidth = size.cx;
    header.biHeight = size.cy;
    header.biSizeImage = NbBytes;
    header.biSize = 40;
    header.biPlanes = 1;
    header.biBitCount = 3 * 8; // RGB
    header.biCompression = 0;
    header.biXPelsPerMeter = 0;
    header.biYPelsPerMeter = 0;
    header.biClrUsed = 0;
    header.biClrImportant = 0;

    // Generate handle
    HANDLE handle = (HANDLE)::GlobalAlloc (GHND,sizeof(BITMAPINFOHEADER) + NbBytes);
    if(handle != NULL)
    {
    // Lock handle
    char *pData = (char *) ::GlobalLock((HGLOBAL)handle);
    // Copy header and data
    memcpy(pData,&header,sizeof(BITMAPINFOHEADER));
    memcpy(pData+sizeof(BITMAPINFOHEADER),pPixelData,NbBytes);
    // Unlock
    ::GlobalUnlock((HGLOBAL)handle);

    // Push DIB in clipboard
    OpenClipboard();
    EmptyClipboard();
    SetClipboardData(CF_DIB,handle);
    CloseClipboard();
    }

    // Cleanup
    MemDC.DeleteDC();
    bitmap.DeleteObject();
    delete [] pPixelData;

    EndWaitCursor();
    }

    • Mr

      Posted by Phil O on 06/06/2014 05:59am

      If you're getting the grey box, the glReadPixels isn't working and that may be because you've not loaded a valid context using wglMakeCurrent().

      Reply
    Reply
  • How can I save a graphic as a JPG file?

    Posted by Legacy on 10/17/2002 12:00am

    Originally posted by: Shujie

    I use VC++ and OpenGL. I want to save a graphic as a JPG file. How can I do it?
    Thanks!

    Reply
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