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..

Google

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

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