The best way to stop flickering is to have another member variable, and to redraw only when necessary. For instance, I chance the cursor every now but that can cause significant redrawing. Using an extra variable, I only redraw when necessary.
void COGraphCtrl::OnPaint()
{
if(m_RePaint)
{
CPaintDC dc(this);
dc.FillSolidRect(&clientRect,RGB(255,255,255));
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void COGraphCtrl::OnPaint()
{
CPaintDC dc(this);
GetClientRect(&clientRect);
GetClientRect(&graphRect);
graphRect.DeflateRect(marginRect);
//Get the X XNorm and offset
xNorm = (graphRect.Width() / (maxXVal - minXVal));//%%%%
xOffset = -minXVal + (marginRect.left / xNorm);
int xN = ((int)xNorm);
m_PointRectWidth = xN<=1?1:xN>4?4:xN;//allowing width 1 - 4
//Get the Y YNorm and offset
yNorm = (graphRect.Height() / (maxYVal - minYVal));
yOffset = -(minYVal);
// Create memory dc and update it's mapping state
CDC memDC;
memDC.CreateCompatibleDC(&dc);
memDC.SetMapMode(dc.GetMapMode());
memDC.SetViewportOrg(dc.GetViewportOrg());
memDC.IntersectClipRect(clientRect);
// Create memory bitmap
CBitmap bmp;
bmp.CreateCompatibleBitmap(&dc, clientRect.Width(), clientRect.Height());
CBitmap* pOldBmp = memDC.SelectObject(&bmp);
//Draw
Draw(&memDC);
//Blit to the original dc
dc.BitBlt(clientRect.left, clientRect.top, clientRect.Width(), clientRect.Height(), &memDC, clientRect.left, clientRect.top, SRCCOPY);
// Restore old bitmap
memDC.SelectObject(pOldBmp);
if(!m_FullyLoaded)
m_FullyLoaded = true;
}