Writing Windows Screensavers in C

It is quite simple to use C to write a screensaver because there is a screensaver library with the commonly required functions and detailed examples with most compilers.

N.B. This article is now quite dated although should still produce a working screensaver. The code segments are from the 16-bit SDK.

Summary

• Add the description to the .DEF file.
• Add the correct EXPORTS to the project
• Include the <scrnsave.h> <windows.h> headers.
• Include scrnsave.lib in your linker options
• Add the standard variables required for the screensaver library.
• Use ScreenSaverProc as the main entry point for your code.
• Use DefScreenSaverProc to handle all the messages that you don't handle.
• Configure your screensaver from ScreenSaverConfigureDialog

DESCRIPTION 'SCRNSAVE :Interesting Title'
EXETYPE     WINDOWS
EXPORTS
            SCREENSAVERPROC                  @1
            SCREENSAVERCONFIGUREDIALOG       @2
            ARROWCONTROLPROC                 @3
            DLGCHANGEPASSWORD                @4
            DLGGETPASSWORD                   @5
            DLGINVALIDPASSWORD               @6
            HELPMESSAGEFILTERHOOKFUNCTION    @7

Headers and associated requirements

Don't forget to #include <scrnsave.h> and #include <windows.h>

Also include scrnsave.lib in the linker options for your development environment

char szAppName[40];

// Externals defined in SCRNSAVE.LIB. Required for all screen savers.

HINSTANCE _cdecl hMainInstance;
HWND _cdecl hMainWindow;
char _cdecl szName[TITLEBARNAMELEN];
char _cdecl szIsPassword[22];
char _cdecl szIniFile[MAXFILELEN];
char _cdecl szScreenSaver[22];
char _cdecl szPassword[16];
char _cdecl szDifferentPW[BUFFLEN];
char _cdecl szChangePW[30];
char _cdecl szBadOldPW[BUFFLEN];
char _cdecl szHelpFile[MAXFILELEN];
char _cdecl szNoHelpMemory[BUFFLEN];
UINT _cdecl MyHelpMessage;
HOOKPROC _cdecl fpMessageFilter;

szAppName

Procedures

The main part of the screensaver is the ScreenSaverProc.

/* ScreenSaverProc - Main entry point for screen saver messages.
 *  This function is required for all screen savers.
 *
 * Params:  Standard window message handler parameters.
 *
 * Return:  The return value depends on the message.
 *
 *  Note that all messages go to the DefScreenSaverProc(), except
 *  for ones we process.
 */
LONG FAR PASCAL __export ScreenSaverProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)

WM_CREATE

Initialise and start a timer with the SetTimer function

WM_TIMER

Do the animation

WM_DESTROY

Finish the screensaver

WM_ERASEBKGND

You can set the background if you need to.

Everything else

Do everything else with DefScreenSaverProc(hWnd, msg, wParam, lParam)

/* ScreenSaverConfigureDialog -- Dialog box function for configuration
 * dialog.
 *
 * Params:  hWnd -- Handle to window
 *
 * Return:  None
 */
BOOL FAR PASCAL __export ScreenSaverConfigureDialog(HWND hDlg, UINT msg, WPARAM wParam, LPARAM lParam)

FARPROC fpDialog;

if((fpDialog = MakeProcInstance(DlgChangePassword,hMainInstance)) == NULL)
    return FALSE;
DialogBox(hMainInstance, MAKEINTRESOURCE(DLG_CHANGEPASSWORD),hDlg, fpDialog);
FreeProcInstance(fpDialog);

Example Source Code

DOWNLOAD 16bit C Source Code