How to avoid flickering in mfc

This is a discussion on How to avoid flickering in mfc within the Windows Programming forums, part of the Platform Specific Boards category; Hi everyone, I am working in mfc SDI application,I have many drawing in that,while scrolling the window lot of flickering ...

  1. #1
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    Mar 2010
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    How to avoid flickering in mfc

    Hi everyone,

    I am working in mfc SDI application,I have many drawing in that,while scrolling the window lot of flickering occurs,Somebody suggests to use Double buffering.But i dont know how to implement in my code.Can any one pls give me some samples,(Drawings drawn using function calling,getting the view pDC like that),..

    Thanking for any comments,

    Shiva..

  2. #2
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    Google

    if that link doesn't work just Google "mfc double buffering".

  3. #3
    train spotter
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    Search here, I have posted code and details before. If you can't find it or have troubles post again (with code would help) and I will try to assist.

    Generally.....

    Ensure you are handling the OnEraseBkgnd() and returning true.

    Ensure you are only calling for a paint when required (minimum amout of InvalidateRect() calls).

    Ensure you use InvalidateRect() with the minimum rectangle possible.

    Follow each InvalidateRect() with an UpdateWindow() [this causes the paint msg to be posted directly to the window's callback, not to the OS msg queue, speeding up paint.]

    Ensure your paint is not using the entire client rect and is using the rect / region returned in the PAINTSTRUCT or GetUpdateRect().


    Code:
    //this code is a rough guide, not working code 
    //it is a quick cut and paste from multiple methods
    
    //I have a base class that does all the create and clean-up 
    //the individual drawing code is in the derived class
    
    //I also prefer to return an error than throw / ASSERT()
    
    //you will need to tailor this code to your needs.
    
    //in .h
    #define		WHITE					RGB(255,255,255)
    CBitmap		*m_ScrOrBmp;	//this si the original 1x1 black and white BMP we get in a created DC, we save it till we need to delete the DC
    CBitmap		m_ScrBmp;	//this is our created BMP with size equal to the client area and colour depth of the main screen
    CDC		m_ScrDC;		//this is the DC to hold our created BMP. We use this DC to do all the drawing, and then call for a paint to copy this DC to the screen
    
    
    //in cpp
    void CMyDialog::OnCreate()
    {
    	BITMAP		BMP;
    	CDC		*pDC;
    
    	GetClientRect(Rect);
    	if(!Rect.Width() || !Rect.Height())//window not yet sized
    		return ERROR;
    
    	//create a memory DC and bitmap
    	HDC	hdc=::GetDC(NULL);
    	m_ScrDC.Attach( ::CreateCompatibleDC(hdc));
    	m_ScrBmp.Attach(::CreateCompatibleBitmap(hdc,Rect.Width(),Rect.Height()));
    
    	//catch the returned BMP so we can return the DC to the original state before we delete it
    	m_ScrOrBmp=m_ScrDC.SelectObject(&m_ScrBmp);
    
    	//fill the client area with a solid white colour
    	CBrush		Brush;
    	Brush.CreateSolidBrush(WHITE);
    
    	//fill area
    	m_ScrDC.FillRect(&Rect,&Brush);
    
    	//clean up 
    	::ReleaseDC(NULL,hdc);
    	Brush.DeleteObject();
    }
    
    void CMyDialog::OnPaint()
    {
    	CPaintDC dc(this); // device context for painting
    	CRect			Rect;
    	GetUpdateRect(Rect,0);
    	if(IsRectEmpty(Rect))
    		GetClientRect(Rect);
    	dc.BitBlt(Rect.left,Rect.top,Rect.Width(),Rect.Height(),&m_ScrDC,Rect.left,Rect.top,SRCCOPY);
    }
    
    void CMyDialog::OnClose()
    {
    	// test to ensure we do not try to release a NULL DC
    	if(m_ScrDC->m_hDC)
    	{
    		//put the original BMP back
    		m_ScrDC->SelectObject(m_ScrOrBmp);
    
    		//now the created BMP is not selected into a DC we can delete it
    		m_ScrBmp->DeleteObject();
    
    		//now the created DC is back to its original state we can delete it
    		m_ScrDC->DeleteDC();
    
    		//make sure our test is valid by setting the HDC member to NULL
    		m_ScrDC->m_hDC=NULL;
    	}
    }
    
    //add methods to draw to m_ScrDC and then call a paint msg
    
    //add a method to handle size changes, delete the current BMP and DC and create a new set the required size
    Last edited by novacain; 03-07-2010 at 11:28 PM. Reason: Added code as I had a few minutes, and clarity / typos
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