Zooming In on a Selection: Step 4

HDC ThisWindowDC;
/* Use GDI functions to outline the area to be cropped. */
if (nFlags == MK_LBUTTON)
{
ThisWindowDC = ::GetDC(this->m_hWnd);
SavedPen = (HPEN)::SelectObject(ThisWindowDC, GetStockObject(WHITE_PEN));
SavedBrush = (HBRUSH)::SelectObject(ThisWindowDC, GetStockObject(NULL_BRUSH));
DisplayMode = GetROP2(ThisWindowDC);
SetROP2(ThisWindowDC, R2_NOT);
if (FirstDraw == FALSE)
Rectangle(ThisWindowDC, StartGDIX, StartGDIY, EndGDIX, EndGDIY);
EndGDIX = point.x;
EndGDIY = point.y;
Rectangle(ThisWindowDC, StartGDIX, StartGDIY, EndGDIX, EndGDIY);
FirstDraw = FALSE;
SetROP2(ThisWindowDC, DisplayMode);
::ReleaseDC(this->m_hWnd, ThisWindowDC); 

}