How to eliminate flickering with erase background in mfc - visual-c++

Question

I am working with SDI app to redraw graph and update data by using timer in View file. Even though I use ON_WM_ERASEBKGND to eliminate flickering, but it still happen. And below are my code that I tried to implement. Anyone has any ideas to eliminate flickering?
Here are my MSG_MAP
ON_WM_PAINT()
ON_WM_ERASEBKGND()
ON_WM_TIMER()
BOOL CVCDSOView::OnEraseBkgnd(CDC* pDC)
{
// TODO: Add your message handler code here and/or call default
return TRUE;
return CView::OnEraseBkgnd(pDC);
}
void CVCDSOView::OnInitialUpdate()
{
CView::OnInitialUpdate();
CRect Rect;
GetClientRect(&Rect);
CRect m_rcDraw = Rect;
// set timer with 200ms
SetTimer(ID_LABEL_COMPANY,200,NULL);
labelCompany.Create(_T("Company"), WS_CHILD | WS_VISIBLE,
CRect(LEFT_SIDE, TOP_SIDE, RIGHT_SIDE+50, BOTTOM_SIDE), this, ID_LABEL_COMPANY);
textboxCompany.Create(WS_CHILD | WS_VISIBLE | WS_TABSTOP | WS_BORDER | ES_NOHIDESEL,
CRect(LEFT_SIDE, TOP_SIDE+VERTICAL_OFFSET, RIGHT_SIDE+50, BOTTOM_SIDE+VERTICAL_OFFSET), this, ID_EDITTEXT_COMPANY);
}
// CVCDSOView message handlers
void CVCDSOView::OnPaint()
{
CPaintDC dc(this); // device context for painting
// TODO: Add your message handler code here
CRect Rect;
GetClientRect(&Rect);
CDC dcMem;
CBitmap bmpMem;
dcMem.CreateCompatibleDC(&dc);
bmpMem.CreateCompatibleBitmap(&dc,Rect.Width()- GRID_LEFT,Rect.Height()-35);
dcMem.SelectObject(&bmpMem);
dcMem.FillSolidRect(Rect, RGB(255,255,255));
CRect m_rcDraw = Rect;
m_rcDraw.DeflateRect(GRID_LEFT,GRID_TOP,GRID_RIGHT,GRID_BOTTOM);
DrawGrid(&dcMem,m_rcDraw);
dc.BitBlt(0,0,Rect.Width(),Rect.Height(),&dcMem,0,0,SRCCOPY);
dcMem.DeleteDC();
DeleteObject(bmpMem);
// Do not call CView::OnPaint() for painting messages
}
void CVCDSOView::OnTimer(UINT nIDEvent)
{
// TODO: Add your message handler code here and/or call default
//
if(nIDEvent==ID_LABEL_COMPANY)
{
CollectData();
Invalidate();
CView::OnTimer(nIDEvent);
}
}
Any idea would be great appreciate.

Answer 1

You have child controls which can cause flicker when their background is painted. You want to exclude the child controls from paint area by adding WS_CLIPCHILDREN flag to the view class:
BOOL CVCDSOView::PreCreateWindow(CREATESTRUCT& cs)
{
cs.style |= WS_CLIPCHILDREN;
return CView::PreCreateWindow(cs);
}
Unrelated to flickering issue:
Don't subtract anything for main rectangle. You should change the bitmap to
bmpMem.CreateCompatibleBitmap(&dc, Rect.Width(), Rect.Height());
You don't need dcMem.DeleteDC() and DeleteObject(bmpMem) MFC will automatically delete these objects.
Note that MFC will not automatically de-select objects. This usually doesn't matter because Windows will do the necessary cleanup, as is done in this example. But for completeness sake add the following:
CBitmap* oldbitmap = (CBitmap*)dcMem.SelectObject(&bmpMem);
...
dc.BitBlt(0,0,Rect.Width(),Rect.Height(),&dcMem,0,0,SRCCOPY);
dcMem.SelectObject(oldbitmap);

Answer 2

In OnEraseBkgnd you should return FALSE.
All drawing in OnPaint should better be done with CMemDC class, because drawing straight on the screen will most likely cause flickering as well:
CMemDC memDC(*pDC, this);
CDC& rDC = memDC.GetDC();
rDC.ActualDrawing`...