Example Screen Savers

(c) 1996-2003 Lucian Wischik, www.wischik.com/scr

Question: How to design the best "screensaver framework?"

Answer: After seven years experience in designing savers and frameworks, my final conclusion is -- don't. Don't make a framework. Instead, make a complete, self-contained, minimal saver that doesn't impose any structure on the programmer and doesn't require to be "learnt". Keep it simple. Accordingly, I present five very basic screen savers. They cover most of the important areas:

• jpegs, bitmaps, transparency for sprites, playing audio, listening to audio, using zipped datafiles embeded as resources rather than as separate files, 3d-opengl, changing screen mode, multi-monitor support, Plus!-style configuration dialogs, passwords under Win95/98/ME, and installation/uninstallation.

These examples complement my technical article, How To Write a 32bit Screen Saver. That article goes into exhaustive detail about exactly how a saver must behave. To understand the internals of these examples, read the article.

Here's what else I've learnt -- the following guidelines, along with the example code, is the distilled "best practice" from years of programming savers and millions of downloads. These guidelines will reduce the effort to design, debug and distribute your savers, and will reduce the number of support-emails you have to answer:

• Use global variables for the saver's settings. I know this goes against one's normal instinct, but in this case a saver's settings are inherently global: they're loaded from the registry upon startup, modified by the configuration dialog, and saved to the registry when you click the "OK" button. There's no need to keep multiple copies of them. Just make them global.
• Allocate resources lazily (ie. upon first use) so far as possible. That means: initialize a global handle or pointer to 0, and in your OnPaint handler or wherever where you first use it, then check whether it's still 0 and if so create it. The check gets performed every single cycle, but it's not costly.
• Combine installer/uninstaller/saver in a single executable. That is, create a single executable called "saver_setup.EXE". When the user runs it, it installs itself (including uninstall support) by copying itself into the Windows directory but renamed as "saver.SCR". There it behaves like a normal saver. When it's run with the argument /u, it behaves like an uninstaller.
• Single self-contained file for the saver. Don't use any additional files: instead, embed all your artwork and music as resources within the saver. This means you have to compress them. I have included example savers to show how to uncompress and use resources that are OGG music files, ZIP files, JPEG pictures. I rewrote the standard public OGG and ZIP source code to make them easier to use, and (in the latter case) to avoid the need for temporary files: instead, zipping happens directly from resource to memory buffer.
• Watch for gradual leaks. A screen saver might run for hours or days on end. If there is any memory or resource leak, it will eventually cause problems. Be very careful, and use the Task Manager to monitor program size and GDI heap.
• Multiple monitors - their time has come. Program from the ground up with multi-monitors in mind. It's usually too hard to retrofit support at a latter stage. Plan in advance: which variables are global (shared between all screens and maybe also the configuration dialog), which are specific to a particular screen. Music, for instance, shouldn't be played by every monitor's saver window.
• Use plain Win32 API. This gives smallest filesizes, and gives the greatest control over the saver's behaviour. Also, you will still be able to read and compile your source code in the future, since it's not tied to any version of any particular development environment.
• Beware bandwidth. After putting a saver online in August 2002, I suddenly noticed in September that it had been downloaded hundreds of thousands of times and lumped me with a US$400 bill for excess bandwidth. Be careful!

Debugging and Deployment

Copy the "scrprev.exe" utility into your Windows directory. Test the saver with arguments

Note: const tstring DebugFile=_T("OutputDebugString") at the start of the file. This will log interesting events, and will also run the saver in "friendly" mode (i.e. not topmost, doesn't quit as soon as it looses focus or the mouse moves). Before deployment you MUST change this.

Make sure you change the two STRINGTABLE resources: 1 is the name of the saver, and 2 is its url for Add/Remove Programs. (you can remove 2 if there isn't a web page).

When you have finished, rename the saver to "mysaver_setup.exe" and deploy it. The extension ".exe" will make the auto-self-installer happen when the user double-clicks on it.

The Example Savers

To create a new saver, I copy the directory from an old one, rename all the files, open them all up in Notepad and alter the names using search/replace. Don't forget the STRINGTABLE resources in the .rc file, and the VERSIONINFO, and the manifest.

There are project files for Visual C++6, Visual C++ .NET and Borland C++Builder5. I'm sure the code will work fine under other compilers. If you want, you can delete the project files for compilers you're not using. The extensions are:

Each example has pretty much the same structure. All the saver code is contained in a single .cpp file that looks like this:

MinScr -- this saver doesn't do anything special, just blobs on the screen using double-buffering. It's a good starting point.

Images -- this saver uses images. It draws a sprite (BMP with transparency) on top of a background (JPG). What's special is that it stores the sprite and background compressed in a ZIP file, and this zip is in turn stored as a resource in the .SCR file. At runtime, when the images are needed, they're decompressed directly from resource into memory without any intermediate files.

PlayOgg -- this saver plays music from an OGG file that's embedded as a resource. I used to think music in a screen saver was silly (because savers are run when you're not at the computer!) But I was wrong: for some of my musical savers, I've had lots of happy parents write to me that their young children are transfixed by the combination of music and images. OGG is a file format that's like MP3 only better.

AudioIn -- this saver captures the currently-playing sound (be it from CD or Windows Media Player or whatever) and displays a voiceprint of it.

ThreeDee -- uses OpenGL for hardware-accelerated 3D graphics. Also optionally changes the screen mode, so as to run faster. There are lots of troublesome fiddly issues to do with 3d graphics and with mode changing: read the comments at the start of threedee.cpp.

By Lucian Wischik, University of Bologna. June 2003.