DwmExtendFrameIntoClientArea function (dwmapi.h)

Extends the window frame into the client area.

HRESULT DwmExtendFrameIntoClientArea(
  [in] HWND          hWnd,
  [in] const MARGINS *pMarInset
);

[in] hWnd

The handle to the window in which the frame will be extended into the client area.

[in] pMarInset

A pointer to a MARGINS structure that describes the margins to use when extending the frame into the client area.

If this function succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.

This function must be called whenever Desktop Window Manager (DWM) composition is toggled. Handle the WM_DWMCOMPOSITIONCHANGED message for composition change notification.

Use negative margin values to create the "sheet of glass" effect where the client area is rendered as a solid surface with no window border.

The following sample demonstrates how to extend the bottom margin, creating a large bottom frame.

HRESULT ExtendIntoClientBottom(HWND hwnd)
{
   // Set margins, extending the bottom margin
   MARGINS margins = {0,0,0,25};
   HRESULT hr = S_OK;

   // Extend frame on the bottom of client area
   hr = DwmExtendFrameIntoClientArea(hwnd,&margins);
   if (SUCCEEDED(hr))
   {
      // ...
   }
   return hr;
}

The following sample demonstrates the "sheet of glass" effect where the client area is rendered without a window border.

HRESULT ExtendIntoClientAll(HWND hwnd)
{
   // Negative margins have special meaning to DwmExtendFrameIntoClientArea.
   // Negative margins create the "sheet of glass" effect, where the client area
   // is rendered as a solid surface with no window border.
   MARGINS margins = {-1};
   HRESULT hr = S_OK;

   // Extend the frame across the entire window.
   hr = DwmExtendFrameIntoClientArea(hwnd,&margins);
   if (SUCCEEDED(hr))
   {
      // ...
   }
   return hr;
}

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