FIX: CScrollView::FillOutsideRect() Fills Incorrectly

WINDOWS   | WINDOWS NT

The information in this article applies to:

• The Microsoft Foundation Classes (MFC), included with:

      - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
      - Microsoft Visual C++ 32-bit Edition, version 1.0
  

SYMPTOMS

Calling CScrollView::FillOutsideRect() incorrectly fills the area outside of the scrolling area that belongs to the CScrollView.

CAUSE

In the file VIEWSCRL.CPP, in the Visual C++ MFC\SRC directory, FillOutsideRect() has the following implementation:

   void CScrollView::FillOutsideRect(CDC* pDC, CBrush* pBrush)
   {
      ASSERT_VALID(pDC);
      ASSERT_VALID(pBrush);
      // Fill Rect outside the image
      CRect rect;
      GetClientRect(rect);
      ASSERT(rect.left == 0 && rect.top == 0);
      rect.left = m_totalDev.cy;
      if (!rect.IsRectEmpty())
         pDC->FillRect(rect, pBrush);    // vertical strip along the side
      rect.left = 0;
      rect.right = m_totalDev.cy;
      rect.top = m_totalDev.cy;
      if (!rect.IsRectEmpty())
         pDC->FillRect(rect, pBrush);    // horizontal strip along the
                                         // bottom

   }

This causes the first rectangle filled to have its left border begin at the coordinate "m_totalDev.cy" (the bottom border of the scrollable area of the view) when it should be at the coordinate of the right border of the view (that is, "m_totalDev.cx"). Similarly, the second rectangle filled has its right border ending at the coordinate "m_totalDev.cy" (always the bottom border of the scrollable area of the view) when it should be at the coordinate of the right border of the view.

RESOLUTION

Modify the MFC source file, VIEWSCRL.CPP, to read as follows:

   rect.left = m_totalDev.cx;
   rect.right = m_totalDev.cx;

NOTE: You will need to have your system configured to build from the command prompt. Running the MSVCVARS.BAT or VCVARS32.BAT file in your BIN directory sets your environment correctly.

STATUS

Microsoft has confirmed this to be a bug in the products listed at the beginning of this article. This problem was corrected in the MFC 3.0 included with Visual C++ 2.0.

MORE INFORMATION

To reproduce this problem, open the DIBLOOK MFC sample, and use Class Wizard to map the WM_ERASEBKGND message of CDibView to the following code, taken from the online help for FillOusideRect():

   BOOL CDibView::OnEraseBkgnd(CDC* pDC)
   {
      CBrush br( GetSysColor( COLOR_ACTIVECAPTION ) );
      FillOutsideRect( pDC, &br );
      return TRUE;                   // Erased
   }

The problem occurs with any bitmap that has its height greater than its width. In these conditions, the area defined by

   (BitmapWidth) < x < (BitmapWidth) + (BitmapHeight - BitmapWidth)
   (0)           < y < (BitmapHeight)