FaderWnd - a Window Fader for Windows 2000

Introduction

One of the attractive new features of Windows 2000 is the menu and other selections that fade away instead of just disappearing. To see this in operation you need to select "Use transition effects for menus and tooltips" on the "Effects" tab of the Display Properties dialog and then select "Fade effect" in the combo box.

In this article I present a simple MFC class that allows you to apply a similar fading effect to any window you choose - with only one line of code! Don't just close a window - have it fade away! The effect is most appropriate to small windows; I use it most often for splash windows, about boxes and other small dialogs.

To use the code you just add the FaderWnd source and header files to your MFC project, include the header in the relevant source file and construct a CFaderWnd when you want your window to fade. The CFaderWnd object itself takes care of fading your window and then destroying and deleting itself.

The only code you need to write is new CFaderWnd(this). Once the CFaderWnd is constructed you can destroy or hide your window, or call EndDialog if the window is a modal dialog.

void CFadeTestDlg::OnClose() 
{
	new CFaderWnd(this);
	DestroyWindow();
}

void CFadeTestDlg::OnOK() 
{
	if (UpdateData)
	{
		new CFaderWnd(this);
		EndDialog(IDOK);
	}
}

void CFadeTestDlg::OnCancel() 
{
	new CFaderWnd(this);
	EndDialog(IDCANCEL);
}

How it works

The CFaderWnd uses the new layered windows feature and the UpdateLayeredWindow API function. The constructor creates a new topmost window with the WS_EX_LAYERED style (among others) and with the same size and position as the source window (the window to be faded). It then uses UpdateLayeredWindow to fill the new window with a bitmap that is an exact copy of the source window. It also sets up a timer. When the constructor returns the source window can be destroyed (or hidden) and the new window remains visible.

On each timer message CFaderWnd calls UpdateLayeredWindow again with a smaller value of alpha. Reducing the alpha value makes the window increasingly translucent. When alpha is at or very near zero CFaderWnd destroys the window and PostNcDestroy deletes the CFaderWnd object.

The CFaderWnd constructor takes three parameters; it looks like this:

CFaderWnd(CWnd *pWndToFade, UINT nFadeTime = 2000, BYTE byAlpha = 255);

The second and third parameters are optional; the examples above all use the default values for these parameters. For obvious reasons (and if they're not obvious you shouldn't be reading this) the first parameter, which specifies the window to fade, must be supplied.

UpdateLayeredWindow is only available on Windows 2000, so if the code were to call that function directly any program using the CFaderWnd class would fail to run on any other platform. I usually want my programs to run on any Win32 platform but to use the new features when they're available. Therefore the code does not call UpdateLayeredWindow directly. Instead it uses GetProcAddress to find out whether the function is available and calls it through the returned pointer when it is. If the function is not available CFaderWnd quietly deletes itself so it behaves as a no-op on older platforms. Thus you can use CFaderWnd in all your programs without compromising their ability to run on all Win32 platforms.