Zooming In on a Selection: Step 5

In the MainWndProc function, add code to process WM_MOUSEMOVE messages. This code outlines the selection using GDI functions . The code should appear as follows:

/* Use GDI functions to outline the area to be cropped. */ 
if (wParam == MK_LBUTTON) 
   ThisWindowDC = GetDC(hWnd); 
   SavedPen = SelectObject(ThisWindowDC, GetStockObject(WHITE_PEN)); 
   SavedBrush = SelectObject(ThisWindowDC, GetStockObject(NULL_BRUSH)); 
   DisplayMode = GetROP2(ThisWindowDC); 
   SetROP2(ThisWindowDC, R2_NOT); 
   if (FirstDraw == FALSE) 
      Rectangle(ThisWindowDC, StartGDIX, StartGDIY, EndGDIX, EndGDIY); 
   EndGDIX = LOWORD(lParam); 
   EndGDIY = HIWORD(lParam); 
   Rectangle(ThisWindowDC, StartGDIX, StartGDIY, EndGDIX, EndGDIY); 
   FirstDraw = FALSE; 
   SetROP2(ThisWindowDC, DisplayMode); 
return (0); 

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