ioccc/2006/stewart

To build:

    make

Bugs and (Mis)features:

The current status of this entry is:

STATUS: INABIAF - please DO NOT fix

For more detailed information see 2006/stewart in bugs.html.

To use:

    ./stewart width_and_height iterations file > file.xbm
    convert file.xbm file.png

where file is one of:

altar box box2 box3 build carpet
circles cross cross2 cross3 crystal
curve diamonds diamonds2 dragon
dragon2 dragon3 fern gasket gasket_mod
gasket_mod2 ioccc maze octagon pentagon
pentagons rings rings2 spirals spirals2
spirals3 spirals4 squares stars stars2
tree tree2 tree3 tree4 triangle

NOTE: you cannot specify a different width from height; it's one number.

NOTE: convert(1) belongs to ImageMagick.

Try:

    ./try.sh

After running the program on a few files it will ask you if you wish to run it on the remaining files.

The script will try converting the xbm files created by the program to png files. If it does it will list those that exist in the directory, at the end of the script. If you do not have convert(1) it will warn you once. In that case you'll have to open the xbm files in a graphics viewer capable of viewing xbm images. In any case choose your favourite graphics viewer to look at the images created.

Judges' remarks:

Note the interesting choice of using a #define in the output. The selection of input files makes this one endlessly fun to play with. Many image viewers will be able to read the results, as will a reasonably experienced user who can parse formats in their mind. :-)

Author's remarks:

Execution

The program should be run with the following

    ./stewart <m> <n> <ifs>

where:

• m

  • The size of the picture (picture will be m X m in size).

• n

  • The number of iterations to run (More will make for a clearer picture).

• ifs

  • The file to use as input.

The program will spit out an XBM image on standard out. Minimal checking is done on the arguments mainly that there are 3. Wrong arguments will cause the program to bomb out.

Example:

    ./stewart 1024 1000000 gasket > gasket.xbm

Compilation/Testing

The program compiles without warning with gcc -ansi -Wall. lint also seems to like the code. This must be a bug in lint.

The program was tested on Linux on a x86 and NetBSD on an alpha. Only gcc was tested for compilers (4.0.3 and 3.3.3).

Entry originality

In looking through past winning entries, there seem to be only 2 (92 and 94) that generated fractals. Both of those were Julia fractals from the Mandelbrot set. Those do make for some pretty pictures. I figured it would be nice to add some more fractals to the IOCCC, since one hasn't won since 1994.

Instead of something that has already won I figured I would go with another kind of fractal, those from the IFS: Iterated Function System.

Input File

The format of the input file is as follows:

    <num ifs> <x min> <y min> <x max> <y max>
    <a> <b> <c> <d> <e> <f> <p>
    <a> <b> <c> <d> <e> <f> <p>
    <a> <b> <c> <d> <e> <f> <p>
    .
    .
    .

This file describe an IFS.

One of the most well known would be the Sierpinski Gasket:

    3 0 0 1 1
    .5 0 0 .5   0    0 .33
    .5 0 0 .5  .5    0 .33
    .5 0 0 .5 .25 .433 .34

or the fern:

    4 -5.5 0 5.5 11
    0    0    0  .16   0    0  .01
    .85  .04 -.04  .85   0  1.6  .85
    .2 -.26  .23  .22   0  1.6  .07
    -.15  .28  .26  .24   0  .44  .07

etc...

Included in my submission will be a tarball of some IFS files, including one that attempts (not very well) to mimic the IOCCC logo (I figure it can't hurt to attempt to suck up, right?).

(NOTE from Judges: we extracted the files.)

I would try to explain how to create an IFS file but I am not smart enough to condense it down to something that is coherent.

Basically the break down is:

num is the number of equations in the IFS. x (min, max) and y (min, max) define the ranges that will be displayed in the XBM image file.

The a b c d e f are used to iterative find points that lie in the IFS from the algorithm

    x = a * prevx + b * prevy + e;
    y = c * prevx + d * prevy + f;

The p is for the probability that the equation will run.

Obfuscations

The main obfuscation is using a void * as my only variable (aside from the args for main()). This causes me to do much casting and pointer arithmetic to get the correct location and completely does away with any meaning the variables could have. This also makes the code more convenient to read in the current form vs preprocessed. After preprocessing there will be almost 300 casts in the code and I believe they are all needed... (I would double check but my brain is kinda mushy right now from chasing down a segfault in the code.)

The other main obfuscation being that it generates an IFS. Which isn't all that common for a program to do. I mean google only has something like 66,000 hits for "Iterated function system" so that means it is obscure, right?

Some other minor obfuscations

Since I formatted it as a "normal" program I did inject something that on first glance will looks like a possible bug. (When you run it through a C-beautifier this will be removed.)

I decided not to use rand() to generate a pseudo-random number. Instead I use XOR and bit shifting.

The input file is used to make the program flexible and to allow it to generate many different IFSs. This has the added bonus of hiding information about the algorithm.

The use of many magic numbers. I figured if I get yelled about them in a review they must be bad, right?

Silly things

The use of decimal numbers where one would expect hex. Octal numbers where one would expect decimal. Shifts instead of divides.

Using xbm as the output format. This might confuse someone who doesn't have an X background. It happens to be easy but is probably a very bad choice from a file size standpoint. 1024x1024 image is 641k in size.