Most complex ASCII fluid - Honorable mention

Yusuke Endoh

mame@ruby-lang.org

https://github.com/mame/

Judges' comments:

To build:

make endoh1

To run:

./endoh1 < configuration.txt

Try:

./endoh1 < endoh1.c ./endoh1 < pour-out.txt ./endoh1 < fountain.txt

Selected 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 comments:

Synopsis

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

gcc 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 “Smoothed-particle hydrodynamics (SPH)” method.

http://en.wikipedia.org/wiki/Smoothed-particle_hydrodynamics

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 “wall particle” (a particle with 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.

http://en.wikipedia.org/wiki/Marching_squares

Portability

The program requires a C99 compiler; it uses complex types and one-line comments. It also uses usleep , which may require -D_BSD_SOURCE or somewhat to build with no warning. Under these conditions, it should be portable. At least, recent compilers with -std=c99 -Wall -W -Wextra -pedantic says 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.

Obfuscation w/ Spoiler

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 x-axis and y-axis is 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, such as, -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, it is actually meaningful; it extracts “integer part of real part” from a complex value by assigning (and casting) it to an integer-type variable.

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 fields” in Japanese.)

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

Other *.txt files are due to the judges.

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

Acknowledgment

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 judgment.

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