POINT p1;
BOOL b_Drawing;

void CtestrectDlg::OnMouseMove(UINT nFlags, CPoint point)
{
	
	CDC *pdc = GetDC();
	RECT rc;
	CBrush cbr;
	
	cbr.CreateSolidBrush(RGB(128,128,128));
	GetClientRect(&rc);
	
	pdc->FillRect(&rc, &cbr);

	if(b_Drawing){
		cbr.CreateSolidBrush(RGB(128,128,255));
		pdc->SelectObject(&cbr);
		pdc->Rectangle(p1.x, p1.y, point.x, point.y);
	}
	
}

void CtestrectDlg::OnLButtonDown(UINT nFlags, CPoint point)
{
	p1.x = point.x;
	p1.y = point.y;

	b_Drawing = TRUE;
}

void CtestrectDlg::OnLButtonUp(UINT nFlags, CPoint point)
{
	b_Drawing = FALSE;
}