Backfract

About The Program

Backfract is an animated wallpaper program for Unix with X windows. It fills your background window with a fractal image, then every 15 minutes it will update the image by zooming in or out. As it zooms in or it it uses a simple heuristic to try to stay with "interesting" scenes.

Downloading Backfract

Backfract is distributed in source code. It uses the Gnu autoconfig system and should be portable across all Unix/X11R4 or later systems.

This link is to a binary object. You probably don't want to download it directly to your viewer. Download them to a file instead.

The complete source code, backfract-1.1.2.tar.gz (53K)
This should compile on any Unix system with an ANSI C compiler (gcc works great). It's in tar file format, then compressed with gzip, so to unpack it you need a command line like "zcat backfract-1.1.2.tar.gz | tar xvf -". Some web browsers will automatically uncompress this file as it downloads. If you end up with a file much bigger than the size listed above, then this is what happened and you don't need to run zcat.

More Backfract Documentation

Backfract does it's best to find interesting areas to look at. Sometimes it isn't so successful. If it wanders off into a really boring part of the mandelbrot set, then either be patient and wait for it to find its way back to something interesting, or kill the backfract job and restart.

Another problem is that it doesn't always pick very attractive colors to use. Occasionally backfract will come up with a new colormap; so like before, you can either wait for it to get its act together or you can kill it and restart.

Backfract has several options that you may want to use:

-colors n Backfract needs lots of colors to get its smooth shading transitions. This is no problem on systems with 16-bit color or more, but if you have an 8-bit color system this might cause problems. Running something like "backfract -colors 64" will force backfract to use at most 64 colors. By default, backfract will try to use 128 colors.

"backfract -colors 1" will make backfract run in black and white only.

In any case, if backfract can't get all the colors it wants, it will use as many as it can.

-delay n This sets the amount of time between zooms (in seconds). By default it is 900 (fifteen minutes). If you have a really slow computer you may want to make this larger. If you want a constantly changing background, set it to zero!
-nostealth Usually, backfract detaches itself and runs in background mode. This switch tells it not to detach, so you can use control-C to kill it.

Backfract Performance

Computing a fractal is a very compute-intensive operation. On my system, it takes anywhere from about 2 seconds to about 5 minutes to repaint the screen, depending on what part of the fractal is in view. Usually it takes about 10 seconds.

Running "backfract -time" makes backfract compute a 1024×1024 image of a fractal with a very high iteration limit. After computing the image, it prints its run time and exits without drawing anything. This makes a benchmark for a CPU's mardelbrot speed.

Here's a list of some systems and the time reported from running "backfract -time" on an idle system:

System CPU Compiler Time CPU Cycles per
FP Op
  Athlon/1200     gcc 2.96 -O3     12.7s     1.71  
  Pentium-III/733     gcc 2.96 -O3     28.9s     2.38  
  egcs 1.1.2 -O3     34.9s     2.87  
  Pentium-II/266     egcs 1.0.3 -O3     88.6s     2.65  
  gcc 2.7.2.1 -O3     103s     3.07  
  Pentium/133     egcs 1.0.3 -O3     254s     3.79  
  gcc 2.7.2.3 -O3     267s     3.99  
  i486DX/66     gcc 2.6.3 -O3     2470s     18.3  


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Backfract / wms@igoweb.org / 27 November 2000