Overcome Window Flicker While Dragging

While I use the CImageList control for dragging, I found it flickers in the owner window while draging and redraw the client region. I tried Google to find a solution, but there were no result, so I try to solve it myself.

Here's my solution, which I'm very glad share with you!

First, you should register a new window class and create a new top most tool window, and move it's position far off screen(I take 99000), so it's not visible. The code would look like this:

BOOL CImageDragWrapper::Initialize()
{
   if(m_hDragWnd)
   {
      return TRUE;
   }

   WNDCLASSEX wcex;
   wcex.cbSize = sizeof(WNDCLASSEX); 

   if(!::GetClassInfoEx(AfxGetInstanceHandle(), POPWINDOWCLASSNAM, &wcex))
   {   
      wcex.style           = CS_HREDRAW | CS_VREDRAW;
      //specifies default window procedure 
      wcex.lpfnWndProc     = (WNDPROC)DefWindowProc;
      wcex.cbClsExtra      = 0;
      wcex.cbWndExtra      = 0;
      wcex.hInstance       = AfxGetInstanceHandle();
      wcex.hIcon           = LoadIcon(0, IDI_INFORMATION);
      wcex.hCursor         = LoadCursor(NULL, IDC_ARROW);
      wcex.hbrBackground   = (HBRUSH)(COLOR_WINDOW+1);
      wcex.lpszMenuName    = 0;
      wcex.lpszClassName   = POPWINDOWCLASSNAM;
      wcex.hIconSm         = LoadIcon(0, IDI_INFORMATION);   
      RegisterClassEx(&wcex);
   }

   m_hDragWnd = CreateWindowEx(WS_EX_TOPMOST | WS_EX_TOOLWINDOW, POPWINDOWCLASSNAM,
                        _T(""),WS_POPUP | WS_DISABLED |  WS_CLIPSIBLINGS,99000, 
                        0, 6, 6, 0,   0,
                        AfxGetInstanceHandle(),   0   );

   if(m_hDragWnd)
   {
      SetLayeredWindowAttributes(RGB(255,255,255), 100,   /*0x00000001|*/0x0000002);

      ShowWindow(m_hDragWnd, SW_SHOW);
      UpdateWindow(m_hDragWnd);
   }
   return m_hDragWnd != 0;
}

Second, move the window to properly position and paint it's client. The code would look like this:

BOOL CImageDragWrapper::DragBegin(HWND hDragWndOwner,int cxWnd, int cyWnd, 
                int cxHotSpotOffset, int cyHotSpotOffset,
                const POINT& ptCurrentMousePos, HBITMAP hBack, 
				int cxBackOffset, int cyBackOffset)
{
   if(m_hDragWnd)
   {   
      m_hDragWndOwner = hDragWndOwner;
      m_cxHotSpotOffset = cxHotSpotOffset;
      m_cyHotSpotOffset = cyHotSpotOffset;

      POINT ptDest = ptCurrentMousePos;
      ClientToScreen(m_hDragWndOwner, &ptDest);

      ::MoveWindow(m_hDragWnd,
                ptDest.x - m_cxHotSpotOffset, 
                ptDest.y - m_cyHotSpotOffset, 
                cxWnd,
                cyWnd, TRUE);

      //Draw background image for dragging support window
      if(hBack)
      {
         HDC hDC = ::GetDC(m_hDragWnd);
         HDC hMemDC = ::CreateCompatibleDC(hDC);
            
         HBITMAP hbmpOldMem = (HBITMAP)::SelectObject(hMemDC, hBack);
         
         ::BitBlt(hDC, 0, 
               0, 
               cxWnd, 
               cyWnd, 
               hMemDC, 
               cxBackOffset, 
               cyBackOffset, 
               SRCCOPY);         

         ::SelectObject(hMemDC, hbmpOldMem);
         ::DeleteDC(hMemDC);

         ::ReleaseDC(m_hDragWnd, hDC);
      }
   }
   return m_hDragWnd != 0;
}

Third, changes the position and dimensions for dragging support window by calling MoveWindow

Forth, move dragging to support the window's postion far to screen. The code would look like this:

BOOL CImageDragWrapper::DragEnd()
{
   if(m_hDragWnd && m_hDragWndOwner)
   {
      m_hDragWndOwner = 0;
      ::MoveWindow(m_hDragWnd,
                   99000, 
                   0, 
                   6,
                   6, TRUE);
   }
   return m_hDragWnd != 0;
}

Using the Code:

First, in the InitInstance method of CWinApp's subclass add code like this:

   CImageDragWrapper::Initialize();
   CTestDragDialogDlg dlg;
   m_pMainWnd = &dlg;
   int nResponse = dlg.DoModal();
   if (nResponse == IDOK)
   {
      // TODO: Place code here to handle when the dialog is
      //  dismissed with OK
   }
   else if (nResponse == IDCANCEL)
   {
      // TODO: Place code here to handle when the dialog is
      //  dismissed with Cancel
   }

   CImageDragWrapper::Destroy();

Then in dragging the owner window's OnMouseMove, OnLButtonUp method calls DragBegin, DragMove, and DragEnd method of CImageDragWrapper, It's very simple.

Note: you can compare CImageDragWrapper with CImageList by using my sample code!



About the Author

Jehhry23 Lv

I'm come from china, very glad to make friend with you!

Downloads

Comments

  • Is Penis Enlargement an Option to Erectile Dysfunction?

    Posted by anueffifielm on 06/21/2013 12:54am

    Erectile Dysfunction - Is it Psychological? It is also widely spread and well known in many countries [url=http://rxhealth.pw ] how long will an erection last with viagra [/url] read far more Erectile Malfunction and Impotence, Avoid Taboo See How

    Reply
Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • On-demand Event Event Date: February 12, 2015 The evolution of systems engineering with the SysML modeling language has resulted in improved requirements specification, better architectural definition, and better hand-off to downstream engineering. Agile methods have proven successful in the software domain, but how can these methods be applied to systems engineering? Check out this webcast and join Bruce Powel Douglass, author of Real-Time Agility, as he discusses how agile methods have had a tremendous …

  • Remember getting your first box of LEGOS as a kid? How fun it was putting the pieces together, collaborating with your friends to create something new? Now, as an IT professional, assembling and maintaining a Lego-like collaboration infrastructure isn't what you signed up for. Piecing together disparate systems of record for email, web meetings and other applications is about as painful as stepping on a pile of Legos. Download the e-book to learn how implementing a collaboration system connects systems of …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date