C / C++ / MFC

class CEditorView : public CScrollView
{
......
private:
	CBitmap m_bmpMem;//cache
......
}
void CEditorView::OnUpdate(CView* /*pSender*/, LPARAM /*lHint*/, CObject* /*pHint*/)
{
	CSize sizeTotal;
	//Calculate the size of View
	GetViewSize(sizeTotal);
	SetScrollSizes(MM_TEXT, sizeTotal);

	CDC *pDC,memDC;
	CBitmap *pOldBmp;

	pDC = GetDC();
	ASSERT(pDC != NULL);

	memDC.CreateCompatibleDC(pDC);
	memDC.SetMapMode(m_nMapMode);

	m_bmpMem.CreateCompatibleBitmap(pDC,sizeTotal.cx,sizeTotal.cy);
	pOldBmp = memDC.SelectObject(&m_bmpMem);
	OnDraw(&memDC);
	memDC.SelectObject(pOldBmp);

	ReleaseDC(pDC);
	InvalidateRect(NULL);
	UpdateWindow();

}
void CEditorView::OnDraw(CDC* pDC)
{
	CEditorDoc* pDoc = GetDocument();
	ASSERT(pDoc != NULL);
/*
Draw the content in View through pDC.
*/
}
void CEditorView::OnPaint()
{
	CPaintDC dc(this); // device context for painting
	CDC     MemDC;
	CBitmap *pOldBitmap;
	CSize size;

	OnPrepareDC(&dc);

	size = GetTotalSize(); 

	// Need a memory DC
	MemDC.CreateCompatibleDC(&dc);

	//Set MapMode
	MemDC.SetMapMode(m_nMapMode);

	// Select in the bitmap
	pOldBitmap =  MemDC.SelectObject(&m_bmpMem);

	// Blt it
	dc.BitBlt( 0, -size.cy, size.cx, size.cy, &MemDC, 0, -size.cy, SRCCOPY );

	// Clean up
	MemDC.SelectObject(pOldBitmap);

	CScrollView::OnPaint();
}