saving private processor

hi, below is my on draw...
it works fine as below...

code:
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void CEditorView::OnDraw(CDC* dc)
{
      CMemDC pDC(dc);
      OnPrepareDC(pDC);
          CEditorDoc* pDoc = GetDocument();
          ASSERT_VALID(pDoc);
          // TODO: add draw code for native data here - use pDC
           //as the device context to draw to
      
      //
      //Set the mapping mode to LOENGLISH
      //
      pDC->SetMapMode(MM_LOENGLISH);

      //
      //Convert arguments to coordinates to MM_LOENGLISH units.
      //
      CSize szTemp;
      szTemp.cx = pDoc->GetGridX();
      szTemp.cy = pDoc->GetGridY();
      pDC->DPtoLP(&szTemp);


      //
      // then draw the grid lines
      //
      CRect clipBoxRect;
      pDC->GetClipBox(&clipBoxRect);
      for(int x = 10 ; x <= pDoc->GetGridX() ; x += 10) {
            pDC->MoveTo(x, -10);
            pDC->LineTo(x, -pDoc->GetGridY());
      }
      
      for(int y = -10 ; y >= -pDoc->GetGridY() ; y -=10) {
            pDC->MoveTo(10, y);
            pDC->LineTo(pDoc->GetGridX(), y);
      }
}
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it works perfectly fine as below....
now the problem is i wanan add this to my above code

code:
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      //
      //Draw the squares
      //
      for(int i = 0 ; i < 500 ; i ++) {
            for(int j = 0 ; j < 750 ; j ++) {
                  COLORREF color = pDoc->GetSquareColor(i, j);
                  CBrush brush(color);
                  int x1 = (j * 10) + 10;
                  int y1 = (i * -10) - 10;
                  int x2 = x1 + 10;
                  int y2 = y1 - 10;
                  CRect rect(x1, y1, x2, y2);
                  pDC->FillRect(rect, &brush);
            }
      }
--------------------------------------------------------------------------------

when i do this...
all the processing power of the processor is eaten up by the processor....
can someone pls tell me a solution by which i can incorporate the above code to my View's OnDraw such that i can still retain my processing power????
tks a lot...