One of the features that I hear most commonly talked about in Vista is Aero Glass, so I thought I would throw together a quick sample that shows how you can extend the glass region of a window. There’s more information up on MSDN for the curious, but here’s the basic four steps that you need to follow in order to extend glass into a window.

1. Include dwmapi.h and dwmapi.lib in your project.
2. Check to see if glass is enabled (using DwmIsCompositionEnabled()).
3. Extend the glass ‘frame’ into your window (using DwmExtendFrameIntoClientArea()).
4. Paint the area that the glass will go into with an alpha channel of 0 (i.e.- paint it black).

This turns out to be really straightforward. For example, if you wanted to extend the glass on a dialog box by 25 pixels on the top, you could do the following:

case WM_INITDIALOG:
{
    BOOL fIsDWMEnabled = FALSE;
    DwmIsCompositionEnabled(&fIsDWMEnabled);

    if (fIsDWMEnabled)
    {
        MARGINS marginGlass = {0};
        marginGlass.cyTopHeight = 25;

        DwmExtendFrameIntoClientArea(hDlg, &marginGlass);
    }
}
break;

Then all that’s needed is to paint the top area black, and fill in the rest with the dialog box color:

case WM_ERASEBKGND:
{
    HDC hdcDlg = (HDC)wParam;
    RECT rctGlass = {0};
    RECT rctNonGlass = {0};

    GetClientRect(hDlg, &rctGlass);
    CopyRect(&rctNonGlass, &rctGlass);

    rctGlass.bottom = rctGlass.top + 25;
    rctNonGlass.top = rctGlass.bottom;

    FillRect(hdcDlg, &rctGlass, (HBRUSH)GetStockObject(BLACK_BRUSH));
    FillRect(hdcDlg, &rctNonGlass, (HBRUSH)GetSysColorBrush(COLOR_3DFACE));
    return 1;
}
break;

Now of course, I need to add the disclaimer that using the glass effect is expensive - you should use it sparingly.