Knowledge Base

PRB: Font Changes as ActiveX Control Resizes

Article ID: 191126

Article Last Modified on 11/21/2006

Microsoft Foundation Class Library 4.2, when used with:
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 5.0 Professional Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition

This article was previously published under Q191126

SYMPTOMS

When you call SelectStockFont() to select a Stock font property to display text in an ActiveX control, the font of the text changes as the size of the control changes with SetWindowPos() or MoveWindow().

CAUSE

SelectStockFont() selects a scaled font into a device context. This causes the font size to change as the control resizes. However, the natural extent is not changed (m_rcBounds is bigger but m_cyExtent is not). As a result, the stock font doesn't scale perfectly with respect to the size of the control.

RESOLUTION

Here are two possible workarounds for this problem:

Use SetControlSize() instead of SetWindowPos() or MoveWindow() to change the size of the control.

Replace SelectStockFont() with the following code:

      CFontHolder& fntHolder =InternalGetFont();
      HFONT internalhFont = fntHolder.GetFontHandle();

      HFONT hOldFont = (HFONT)::SelectObject(pdc->m_hDC,internalhFont);
      pdc->TextOut(20, 20, "Hello", 5);
      ::SelectObject(pdc->m_hDC,hOldFont);

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

Generate an MFC ActiveX control with the Control Wizard.
Add a Stock font property to the control.

Add a method called SizeControl() to the control. Call SetWindowPos() in this method to change the size of the control. For example:

      void CFontCtrl::SizeControl()
      {
         CRect r;
         GetWindowRect(&r);
         SetWindowPos(NULL, 0, 0,
            r.Width() + 100, r.Height() + 100, SWP_NOMOVE);
      }

Display a text string in the control's OnDraw() function with the Stock font property as shown here:

      void CFontCtrl::OnDraw(CDC* pdc, const CRect& rcBounds,
         const CRect& rcInvalid)
      {
         pdc->FillRect(rcBounds,
            CBrush::FromHandle((HBRUSH)GetStockObject(WHITE_BRUSH)));
         pdc->Ellipse(rcBounds);
         CFont* def_font = SelectStockFont(pdc);
         pdc->TextOut(20, 20, "Hello", 5);
         pdc->SelectObject(def_font);
      }

Build the control project, and then insert the control to the ActiveX Control Test Container.
Invoke the SizeControl() method in the ActiveX Control Test Container. The font of the text changes.

Additional query words: ocx

Keywords: kbprb KB191126