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The International Obfuscated C Code Contest

2012/endoh1 - Most complex ASCII fluid - Honorable mention

ASCII fluid dynamics

← 2012/dlowe ↑ 2012 ↑ 2012/endoh2 → C code Makefile Inventory ✓

Author:

To use:

    make

There are two alt versions that let you control the compile time variables that control the fluid behaviour and the added variables to speed up or slow down the fluid as well as setting a timeout (if not 0): one for the original black and white and one for the colour one added by the author (at the request of the judges at the time of the contest). Another version is the deobfuscated version provided by the author as well. See the Alternate code section below for more details.

    ./endoh1 < file

WARNING: if you’re sensitive to/don’t like flashing colours/text or just want to see what this looks like not going so fast then you might wish to try the Alternate code instead.

Try:

    ./try.bw.sh endoh1.c
    ./try.sh endoh1.c

    ./try.bw.sh pour-out.txt
    ./try.sh pour-out.txt

    ./try.bw.sh fountain.txt
    ./try.sh fountain.txt

Alternate code:

The files endoh1.alt.c and endoh1_color.alt.c correspond to endoh1.c and endoh1_color.c but which allow you to speed up or slow down the fluid and change the behaviour of the fluid. The file endoh1.alt2.c is deobfuscated and was provided by the author.

Alternate build:

For the default values, try:

    make alt

In the alt versions a default time of 10 seconds is set as an alarm so that one can more easily go through the list of files to see them all in succession, for fun. That is controlled by the variable TIMER at compilation. For instance if you wish to change the value to 5:

    make clobber TIMER=5 alt

If you want to disable the alarm time, set it to 0:

    make clobber TIMER=0 alt

It cannot be < 0 or > 60 (arbitrarily selected).

The SLEEP variable is to delay the time between updates to make it easier to see and to not flash too quickly. The code protects against a value < 0 and defaults to 12321 but you can change it to. For instance to slow it down you could increase the sleep time from 12321 to 50000:

    make clobber SLEEP=50000 alt

If you wish to speed it up you might decrease the sleep time from 12321 to 9999:

    make clobber SLEEP=9999 alt

WARNING: the lower the value the faster it will flash so be careful if you’re sensitive to this.

If you wish to change the gravity factor, pressure factor and/or viscosity factor, you should redefine the values GRAVITY, PRESSURE and/or VISCOSITY macros, respectively. For instance if you wish to change the viscosity and pressure factors but leave the other values alone:

    make clobber VISCOSITY=X PRESSURE=Y alt

where X and Y are numbers or the letter I and which are, respectively, the viscosity and pressure factors. There is no attempt to check the value or type because doing so prevents the macros from being defined to I which would prevent the author’s remarks about it from being done.

You might also wish to try redefining the macros G, P and/or V. For instance:

    make clobber GRAVITY=5 PRESSURE=5 VISCOSITY=5 alt

You might try even:

    make clobber GRAVITY=I alt

See the author’s remarks for details on these macros where:

    G = GRAVITY
    P = PRESSURE
    V = VISCOSITY

Alternate use:

Use endoh1.alt, endoh1_color.alt and endoh1.alt2 as you would endoh1 and endoh1_color above.

Alternate try:

To see two different ways run on the source file and each of the text files, try:

    ./try.alt.sh

The second run of each will be with the gravity factor set to I.

To see the same thing but in the original uncoloured version, try:

    ./try.alt.bw.sh

Judges’ remarks:

Let’s play Jeopardy!

A: An obfuscated program that deals with complex numbers and produces animated ASCII graphics. Q: What is a Mandelbrot simulator?

Bzzzt!

Such heavily squeezed fluid simulation (this is parsed uniquely as fluids are not squeezable) has a few quirks that the judges were happy to experiment with.

One configuration file was inspired by an XKCD what if? entry.

Author’s remarks:

Synopsis

DO NOT FORGET -DG=1 -DP=4 -DV=8 and make your terminal window larger than 80 x 25.

    cc endoh1.c -DG=1 -DP=4 -DV=8 -D_BSD_SOURCE -o endoh1 -lm
    ./endoh1 < endoh1.c
    ./endoh1 < logo.txt
    ./endoh1 < column.txt
    ./endoh1 < pour-out.txt
    ./endoh1 < tanada.txt

What it is

    ,___. ,.       ,.    ,.   ,___. ,.              ,.       ,.
    |/--' ||       `'    ||   |/--' `'              ||       |\_.
    |\__. || ,. ,. ,. ,__/|   |\__. ,. ,____. ,. ,. ||  ,_.  |/-'  ,_.  ,__.
    |/--' || || || || |/-\|   `--\| || |/\/\| || || || ,/-\. ||   ,/-\. |/-\.
    ||    || `\_/| || |\_/|   ,__/| || |||||| `\_/| || `\_/\.`\_. `\_/' || `'
    `'    `'  `--' `' `---'   `---' `' `'`'`'  `--' `'  `-'`' `-'  `-'  `'


     ,.,.                      ,.,.
    ,/\/\. ,.       ,.    ,.  ,/\/\. ,.              ,.      ,__.
    |||#/' ||       `' ,_.||  |||#/' `',_.,__.       ||      ||\\.        ,.
    |||#\. || ,. ,. ,.,/#|||  |\//\. ,.|#||##| ,. ,. || ,.,. |\/-' ,.,. ,.|\.
    |\/--' ||,/\.|| |||#/\/|  `\#||| |||#||/\|,/\.|| ||,/'`\.|#|  ,/'`\.|\/-\.
    `\|    ||`\#||| |||#||\|  ,//\/| ||`\|||||`\#||| ||`\.,/\/\|,.`\.,/'`\| `'
     `'    `' `-'`' `'`-'`-'  `-'`-' `' `'`'`' `-'`' `' `'`--'`'`' `'`'  `'


    ,_.,_. ,.       ,.    ,.  ,_.,_. ,.              ,.      ,.
    |#||#| ||       `'    ||  |#||#| `'              ||      ||,_.
    ||\/#| ||,.  ,. ,.,_.,/|  |\||#| ,.,_.,__.,.  ,. || ,.,. |||#| ,.,. ,.,_.
    |||##| ||||  || |||#||#|  |#||#| |||#||##|||  || ||,/||\.||`-',/||\.|||#\.
    ||`--' ||`\_.|| |||\||#|  |#||#| ||||'||\|`\_.|| ||`\||#|`\.,.`\||/'||`--'
    `'     `' |#||| `'|#||#|  |#||#| `'`' `'`' |#||| `' |||/' |||| |||| `'
              `-'`'   `-'`-'  `-'`-'           `-'`'    `'`'  `'`' `'`'

This program is a fluid simulator using the SPH: Smoothed-particle hydrodynamics method.

The SPH particles represent the fluid flow. Particles have information about the position, density, and velocity. In every simulation step, they are changed by pressure force, viscosity force, and external force (i.e., gravity).

This program reads a text from standard input, and uses it as an initial configuration of the particles. The character # represents a “wall particle” (a particle with a fixed position), and any other non-space characters represent free particles.

The compilation options -DG=1 -DP=4 -DV=8 represent, respectively, the factor of gravity, pressure, and viscosity. By changing their values, you can see different fluid behavior.

Marching square-like algorithm is used to render the particles.

Portability

The program requires a C99 compiler; it uses complex types and one-line comments. It also uses usleep(3), which may require -D_BSD_SOURCE or so to build with no warning. Under these conditions, it should be portable. At least, recent compilers with -std=c99 -Wall -W -Wextra -pedantic say nothing.

    gcc -DG=1 -DP=4 -DV=8 -D_BSD_SOURCE -std=c99 -Wall -W -Wextra -pedantic endoh1.c

    clang -DG=1 -DP=4 -DV=8 -D_BSD_SOURCE -std=c99 -Wall -W -Wextra -pedantic endoh1.c

I expect it to work in any Unix-like environment. VTxxx/ANSI sequences are used to clear screen and move cursor to home.

I’ve tested with gcc-4.6.3 and clang-3.0 on Linux (Ubuntu 12.04) and gcc-4.5.3 and clang-3.1 on Cygwin. On Cygwin, gcc and clang complain about a usage of I (complex’s imaginary unit), but I bet this is cygwin’s issue; it is surely a C99 feature.

Notes about Additional Files

logo.txt is a source of the logo in this remark file.

column.txt is a water column collapse, which is a popular demo of SPH.

pour-out.txt pours you a cup of tea.

tanada.txt simulates “Terrace farming”. (“Tanada” means a “terraced rice” in Japanese.)

clock.txt is a “water” clock created by HAMANO Tsukasa.

Other *.txt files are from the judges.

endoh1_color.c is a variant that shows the density by using terminal 256 colors.

Acknowledgments

I would like to thank my wife @hirekoke for her teaching me the SPH method.

The judges ordered suggested creating a color version after the contest.

The judges and HAMANO Tsukasa (The silver medalist at this IOCCC) kindly provided many configuration files.

NOTICE to those who wish for a greater challenge:

If you want a greater challenge, don’t read any further: just try to understand the program via the source.

If you get stuck, come back and read below for additional hints and information.

How this entry works:

First of all, the source code itself serves as an initial configuration. Preprocessing directives (such as #include)’s # serve as walls.

This program uses double complex to represent any 2D vector. But, note that the x-axis and y-axis are swapped (real axis = y-axis, imaginary axis = x-axis). The purpose of swapping is not only obfuscation, but also short coding: for example, to add gravity to total force, force += G suffices, rather than force += G*I.

(Incidentally, you can exert horizontal gravity by using for instance -DG=I)

Every five entries of double complex a[] contain information of one particle: position, wall-flag, density, force, and velocity, in turn.

You can use G, P, and V as a guide to find the calculation code of gravity, pressure, and viscosity forces.

Though some assignments may look meaningless, they are actually meaningful; they extract “integer part of real part” from a complex value by assigning (and casting) it to an integer-type variable.

Inventory for 2012/endoh1

Primary files

Secondary files

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