Creating a Screen Saver with C#
Frank McCown - Harding University

Introduction

A Windows screen saver is simply a Windows application that displays either an options dialog box, a preview screen, or a full-screen window, depending on the command line argument it receives.  Windows screen savers have a .scr extension and are typically stored in the Windows system directory. 

Argument          Action

/c                     Configuration mode

/p                     Preview mode

/s                     Full-screen mode

Your program can determine which mode your program is to execute by examining the command line parameters in Main:

static void Main()

{

       string[] cmdList = Environment.CommandLine.Split(' ');

       // First command-line param is the exe name, second param is the mode

       if (cmdList.Length >= 2) {

              if (cmdList[1].IndexOf("/c") >= 0) {        // Configuration mode

                     Application.Run(new OptionsForm());

                     return;

              }

              parentHwnd = IntPtr.Zero;

              if (cmdList[1] == "/p") {               // Preview mode

                     previewMode = true;

                     // Handle to preview dialog box is next command-line param

                     parentHwnd = (IntPtr) uint.Parse(cmdList[2]);

              }

       }

       Application.Run(new ScreenSaverForm());

}

The parentHwnd will be used in preview mode and is discussed in the preview mode section.  The ScreenSaverForm is a Windows Form that will need to fill the entire screen.  This is done by setting the ScreenSaverForm’s WindowState property to Maximized and FormBorderStyle to None.  The OptionsForm is just a Windows Form that looks like a typical dialog box for setting properties of the screen saver.

Configuration Mode

In configuration mode, the screen saver should launch a dialog box that allows the user to control the appearance and settings of the screen saver.  Typically these settings are stored in the Windows Registry.  The Registry is a hierarchical repository of information used by Windows and applications for storing various types of configuration data.

The following code segment shows how information can be stored in and retrieved from the Registry:

using Microsoft.Win32;

// Store in Registry

RegistryKey key = Registry.LocalMachine.OpenSubKey("SOFTWARE\\Demo_ScreenSaver");

if (key != null)

       Registry.LocalMachine.DeleteSubKeyTree("SOFTWARE\\Demo_ScreenSaver");

key = Registry.LocalMachine.CreateSubKey("SOFTWARE\\Demo_ScreenSaver");

key.SetValue("text", "some text");

// Read from Registry

RegistryKey key = Registry.LocalMachine.OpenSubKey("SOFTWARE\\Demo_ScreenSaver");

if (key != null)

       string text = (string)key.GetValue("text");

You can see the entries made in the Registry by using regedit.  Run regedit by clicking on the Start button in the task bar, selecting Run… and entering “regedit”.  By very careful when using regedit… deleting or altering any information may cause Windows or other applications not to function properly anymore.

Look under “My Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Demo_ScreenSaver” to see your setting.  Close regedit when you no longer need it.

Preview Mode

When the screen saver starts up in preview mode, it should run in a child window whose parent window is the Display Property window as shown in the figure below.  The handle to the Display Properties window is obtained from the second command line parameter when the screen saver is executed in preview mode.

In this mode, you will find the IsWindowVisible and GetClientRect Win32 API functions useful for determining if the Displays Property dialog is still visible and for determining the dimensions of the area you can paint to.

// Quit if dialog is dismissed.  Check this periodically.

if (!IsWindowVisible(parentHwnd))

Application.Exit();

private struct RECT {

public int left, top, right, bottom;

}

RECT rect = new RECT();

if (GetClientRect(parentHwnd, ref rect)) {

Graphics g = Graphics.FromHwnd(parentHwnd);

       g.Clear(Color.Black);

       graphics.DrawString(“Demo Screen Saver”, font, brush, ((float)rect.right - 50),

((float)rect.bottom – 50);

g.Dispose();

}

Full Screen Mode

In full screen mode, your application should run until it receives a mouse move, mouse click, or some other event that indicates it should terminate.  The cursor should be hidden by calling Cursor.Hide();

Demo

An example C# screen saver can be downloaded here.  Unzip the C# project once you have it downloaded.  The screen saver displays text at a random location for a fixed period of time. 

1. Load this project into Visual Studio .NET and build the ScreenSaver.exe.
2. Change the extension of the .exe to .scr.
3. Copy the ScreenSaver.src file to the Windows\System directory where all the other screen savers are located.
4. Launch the Display Property dialog by right-clicking in the Windows desktop and selecting Properties from the pop-up menu.
5. Select the Screen Saver tab located at the top of the dialog box and select “ScreenSaver” from the list of screen savers.  You should see it running in preview mode in the small rectangular area of the dialog.
6. Change the text being displayed by clicking the Settings button.
7. View the screen saver full-size by clicking the Preview button.  Clicking the mouse button when the screen saver is running in full-screen mode will cause it to terminate.

Send any comments or corrections to me at fmccown@harding.edu.