Rename hint.txt and hint.text to README.md
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# Most Diffused Reaction
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Someone Anonymous
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Twitter: @hirekoke
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Yusuke Endoh
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<https://github.com/mame/>
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Twitter: @mametter
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## Judges' comments:
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### To use:
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make
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<tbd-tool-rubl-perl-python?>
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### Try:
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Connect to port http://localhost:10333 with your browser
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### Selected Judges Remarks:
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How did the leopard get its spots? Why are a zebra's stripes unique?
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In case you didn't recognise the portrait of Alan Turing, there are some
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pointers to his features like eyes with "stdeye-o" and "<--mouth". Can you
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find any other tributes?
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## Author's comments:
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What does "Alan Turing" remind you of? Cryptanalysis of the Enigma? Turing machine? Turing test? This program is also based on his work.
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### Whirlwind tour
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Compile the program as follows:
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$ clang -O3 -std=c99 \
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-Wall -Wextra -pedantic -o prog prog.c \
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-Delta_u="Du*laplacian(u)-u*v*v+F*(1-u)" \
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-Delta_v="Dv*laplacian(v)+u*v*v-v*(F+K)" \
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-DF=0.040 -DK=0.060 -DDu=0.200 -DDv=0.100 \
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-DUV_BACKGROUND=1,0 -DUV_DROP=-0.5,0.5 \
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-DTIMESTEP=1.0 -DSPEED=2 -DRGB=255:128:192
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Then, run it under `tcpserver` command in [ucspi-tcp](http://cr.yp.to/ucspi-tcp.html) package, which was created by Daniel J. Bernstein, IOCCC 1989 "Best of Show" winner.
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$ tcpserver -v 127.0.0.1 10333 ./prog ioccc.txt
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Finally, open `http://127.0.0.1:10333/` by a modern browser supporting HTML5. You can use the mouse cursor to place drops into the Petri dish interactively.
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### Description
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This is a simulator of *reaction-diffusion systems*.
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Reaction-diffusion systems, proposed by Alan Turing in [1], are mathematical models in which two chemical substances are transformed into each other (*local chemical reactions*) and spread out (*diffusion*). Their interactions sometimes form non-trivial patterns, such as spots, spiral, dappling, and labyrinths.
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The systems are generally formulated as follows:
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du/dt = F(u, v) + Du * laplacian(u)
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dv/dt = G(u, v) + Dv * laplacian(v)
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The functions `F(u, v)` and `G(u, v)` represent reactions of each substance, and the parameters `Du` and `Dv` are diffusion coefficients. By changing the functions and parameters, you can see a wide range of behaviors.
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See [the Wikipedia article of "Reaction-diffusion system"](https://en.wikipedia.org/wiki/Reaction%E2%80%93diffusion_system) in detail.
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This program simulates the systems. The field consists of 128 x 128 cells. Each cell includes infomration of an amount of the two substances, and interacts with neighbor cells (in terms of von Neumann neighborhood) in each frame.
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### Configuration
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You can change the model, initial pattern, simulation speed, and color via macro definition.
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#### Model: `-Delta_u=<expression> -Delta_v=<expression>`
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The definitions represent the equations of reaction-diffusion system. For example, the following is [the Gray-Scott model](http://groups.csail.mit.edu/mac/projects/amorphous/GrayScott/) in TeX notation.
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\frac{\partial u}{\partial t} = D_u \Delta u - u v^2 + F (1 - u)
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\frac{\partial v}{\partial t} = D_v \Delta v + u v^2 - v (F + K)
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You can specify this model as follows:
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-Delta_u="Du*laplacian(u)-u*v*v+F*(1-u)" \
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-Delta_v="Dv*laplacian(v)+u*v*v-v*(F+K)"
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`Du`, `Dv`, `F`, and `K` are parameters of that model.
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#### Initial pattern: `-DUV_BACKGROUND=<u0>,<v0> -DUV_DROP=<u1>,<v1>`
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The definitions specifies the initial amount of the two substances u and v. All cells have `(u0, v0)` by default.
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You can specify a pattern file when the executable is invoked (not compile-time). The file should include a sequence of points, see `ioccc.txt`, `center.txt`, or `line.txt` as examples. Each amount in cells near to the point included in the file, will be added by `(u1, v1)`.
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#### Simulation speed: `-DTIMESTEP=ts -DSPEED=spd`
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The definitions are for changing the simulation speed.
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`TIMESTEP` is a simulation time step. The bigger, the faster but more unstable.
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`SPEED` is a frameskip parameter. The bigger, the faster but more sluggish.
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#### Rendering color: `-DRGB=r:g:b`
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This specifies a color used for rendering.
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### Examples
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Some interesting parameters are included in `Makefile`. Do one of the following command and open `http://127.0.0.1:10333`.
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$ make gray-scott-1 && tcpserver -v 127.0.0.1 10333 ./gray-scott-1 ioccc.txt
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$ make gray-scott-1 && tcpserver -v 127.0.0.1 10333 ./gray-scott-1 center.txt
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$ make gray-scott-1 && tcpserver -v 127.0.0.1 10333 ./gray-scott-1 line.txt
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$ make gray-scott-2 && tcpserver -v 127.0.0.1 10333 ./gray-scott-2 ioccc.txt
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$ make gray-scott-3 && tcpserver -v 127.0.0.1 10333 ./gray-scott-3 ioccc.txt
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$ make gray-scott-4 && tcpserver -v 127.0.0.1 10333 ./gray-scott-4 ioccc.txt
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$ make fitzhugh-nagumo-1 && tcpserver -v 127.0.0.1 10333 ./fitzhugh-nagumo-1 ioccc.txt
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$ make fitzhugh-nagumo-2 && tcpserver -v 127.0.0.1 10333 ./fitzhugh-nagumo-2 ioccc.txt
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$ make oregonator && tcpserver -v 127.0.0.1 10333 ./oregonator ioccc.txt
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These examples are created by drawing (and modifying) the pattern files of [Ready](https://github.com/GollyGang/ready), a cross-platform implementation of various reaction-diffusion systems [2].
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### Compatibility
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#### C part
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This program compiles clean with no warnings under `-std=c99 -Wall -Wextra -pedantic`. Since it uses `long long` for 64bit integers, C99 is required.
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#### Browser part
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You must use a modern browser that supports the latest specification of WebSocket [3]. All the following browsers worked for me:
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* Google Chrome 45
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* Mozilla Firefox 39
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* Microsoft Internet Explorer 11 (works but sluggish)
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I think Safari 6 will work but I haven't tested. (I have no recent os x.)
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#### tcpserver alternatives
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I think you may use `inetd` and `xinetd` instead of `tcpserver`. Here is an example of inetd configuration.
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10333 stream tcp nowait nobody /path/to/prog /path/to/prog /path/to/initial-pattern.txt
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But note that I didn't test well.
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### Internal
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1. The C program accepts HTTP connection from the browser, and sends a HTML document.
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2. The browser tries to upgrade the connection to WebSocket.
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3. The C program accepts WebSocket upgrade. This negotiation process requires SHA1 hash [4] and Base64 encoding [5]. The C program calculates them without the aid of any external libraries.
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4. The C program simulates the reaction-diffusion system, and then send the field data to the browser on each frame.
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4. The browser receives and renders the field data onto the HTML5 canvas.
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### References
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* [1] Turing, A. M., "The Chemical Basis of Morphogenesis", Philosophical Transactions of the Royal Society, 1952.
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* [2] The Ready Bunch, "Ready", A cross-platform implementation of various reaction-diffusion systems, since 2011, <https://github.com/GollyGang/ready>.
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* [3] Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC 6455, DOI 10.17487/RFC6455, December 2011, <http://www.rfc-editor.org/info/rfc6455>.
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* [4] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001, <http://www.rfc-editor.org/info/rfc3174>.
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* [5] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, <http://www.rfc-editor.org/info/rfc4648>.
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--------------------------------------------------------------------------------
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<!--
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(c) Copyright 1984-2016, [Leo Broukhis, Simon Cooper, Landon Curt Noll][judges] - All rights reserved
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This work is licensed under a [Creative Commons Attribution-ShareAlike 3.0 Unported License][cc].
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[judges]: http://www.ioccc.org/judges.html
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[cc]: http://creativecommons.org/licenses/by-sa/3.0/
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-->
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