Writing Windows(32bit) Screensavers in C

It is quite simple to use C to write a screensaver for Windows 9x or Windows NT because there is a screensaver library with the commonly required functions and detailed examples with most compilers. The details here assume that you will be using a single windows timer to control your animation.

Summary

• Add the name of the screensaver to the resources
• Include the <scrnsave.h> <windows.h> headers.
• Add scrnsave.lib to the linker options of your development environment.
• 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

• Name = Description
• ID = 1 (this is specified in the Screensave.h)
• Maximum length of 25 characters

e.g.

STRINGTABLE DISCARDABLE 
BEGIN
    Description             "Mr Bump Screensaver"
END

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

The <scrnsave.h> is a useful reference of requirements for using the screensaver and library and is worth checking to see if has more recent recommendations to this document.

This file requires your to add scrnsave.lib to the linker options of your development environment

You also need the following variables to run the library.

char szAppName[40];

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.
 */
LRESULT WINAPI 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

LRESULT WINAPI DefScreenSaverProc (HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)

See #include <scrnsave.h> for details of what this function does.

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

Unlike 16bit screensavers you no longer need to provide a change password button on the dialog. See security section for more details of passwords.

FARPROC fpDialog;

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

/* To allow the programmer the ability to register child control windows, this
 * function is called prior to the creation of the dialog box.  Any
 * registering that is required should be done here, or return TRUE if none
 * is needed...
 */
BOOL WINAPI RegisterDialogClasses (HANDLE hInst) 
{
    return TRUE;
}