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<h1>The International Obfuscated C Code Contest</h1>
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<h2>2013/hou - Best use of one infinite loop</h2>
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<h3>ray tracer</h3>
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<a class="Left" href="../endoh4/index.html">← 2013/endoh4</a>
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<h2 id="author">Author:</h2>
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<ul>
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<li>Name: <a href="../../authors.html#Qiming_HOU">Qiming HOU</a><br>
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Location: <a href="../../location.html#CN">CN</a> - <em>People’s Republic of China</em> (<em>China</em>)</li>
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<p>https://github.com/ioccc-src/winner/blob/master/## To build:</p>
|
||
<pre><code> make all</code></pre>
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||
<h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
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||
<p>The current status of this entry is:</p>
|
||
<blockquote>
|
||
<p><strong>STATUS: INABIAF - please DO NOT fix</strong></p>
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||
</blockquote>
|
||
<p>For more detailed information see <a href="../../bugs.html#2013_hou">2013/hou in bugs.html</a>.</p>
|
||
<h2 id="to-use">To use:</h2>
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<pre><code> ./hou [scene-file-name] [options]</code></pre>
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<p>Follow the instructions in <code>stdout</code>, preferably with an auto-refreshing PPM
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image viewer ready. Refresh the image every time the output refreshes, all
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effects should be more or less recognizable when you see 16.</p>
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<h2 id="try">Try:</h2>
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<pre><code> ./try.sh</code></pre>
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<p>Try opening the file noted by the program then let the program run a while and
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every so often reopen the file, to see how it changes. The author suggests that
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you leave the program running overnight to see what happens. If however you do
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not have all night :-) then the following JPEG files should show you what
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||
happens with some of the invocations above:</p>
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<p><img src="luna.jpg"
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alt="artificial image showing a room lit by light from a window"
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width=640 height=480></p>
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alt="artificial image showing IOCCC 2013 in a room with stars on the floor and double helix in the backgrond"
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width=640 height=480></p>
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<p><img src="otherroom.jpg"
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alt="artificial image the background double helix"
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width=320 height=240></p>
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<p>This program does not terminate by itself: you must kill <code>hou</code> (but not Qiming
|
||
Hou :-) ) in order to end the program.</p>
|
||
<h2 id="judges-remarks">Judges’ remarks:</h2>
|
||
<p>You could consider that this program violates the source code size
|
||
limit. This is because the first compilation of this program is
|
||
really just a decompressor to generate the real source code of the
|
||
program.</p>
|
||
<p>This program will loop infinitely while progressively refining a
|
||
<a href="https://en.wikipedia.org/wiki/Ray_tracing_(graphics)">raytraced</a> image.</p>
|
||
<p><strong>NOTE</strong>: the author refers to <code>a.c</code>, placed in a gzipped file <code>a.c.gz</code>. We do not
|
||
include it but it can be generated like:</p>
|
||
<pre><code> make a.c</code></pre>
|
||
<p>There is no longer a need to do this as the Makefile takes care of it without
|
||
even needing to create a temporary file but as the author refers to it and its
|
||
uses it can still be generated to follow along.</p>
|
||
<h2 id="authors-remarks">Author’s remarks:</h2>
|
||
<h3 id="using-hou">Using hou</h3>
|
||
<p>This program is a programmable rendering engine with a built-in default scene.
|
||
The standard command line is:</p>
|
||
<pre><code> ./hou [scene-file-name] [options]</code></pre>
|
||
<p>As <code>hou</code> runs, it writes a progressively refining image to a ppm file specified
|
||
in the scene. The initialization may take a while, but once it’s done, a rough
|
||
preview should be available in seconds. Leave <code>hou</code> running for the night, and you
|
||
get a high quality result like the attached <code>*.jpg</code> files. Kill <code>hou</code> manually
|
||
after you’re satisfied with the image quality.</p>
|
||
<p>To save time and energy for the judges, rendered images for all provided scenes
|
||
are provided as attached files.</p>
|
||
<h3 id="features">Features</h3>
|
||
<ul>
|
||
<li>Fully programmable: Almost every stage of the renderer is programmable with
|
||
a shader, i.e., a short script that does something rendering-related. In
|
||
particular, each scene consists of one or more geometry shaders, a camera
|
||
shader, and one or more material shaders. Shaders are written in an
|
||
interpreted language that supports basic arithmetic, a few math functions,
|
||
variables and procedural calls in the CPS (Continuation Passing Style).</li>
|
||
<li>Fast preview: This renderer isn’t just a naive path tracer, it actually uses a
|
||
modern global illumination algorithm which is robust against challenging scene
|
||
configurations. You can mostly place light sources and specify surface
|
||
properties as you please without worrying too much about the convergence speed;
|
||
you always get a nice fast preview within one or two minutes. As proof, there
|
||
is a comparison: <code>./hou otherroom.scene</code> gives a rough idea about the overall
|
||
illumination at 16 samples per pixel (i.e., when the program prints 16), whereas
|
||
the naive approach <code>./hou otherroom.scene NAIVE</code> only produces a mess of white
|
||
dots.</li>
|
||
<li>Rich visual effects: The algorithm samples all light path types so most
|
||
physically based effects can be produced. The default scene demonstrates quite a
|
||
few of them: reflection, area light, soft shadows, color bleeding, caustics, and
|
||
depth-of-field blur. Of course, one can also get programmable-shading effects
|
||
like procedural texturing and approximated Fresnel terms.</li>
|
||
<li>Accelerated ray tracing: The ray tracing part uses an algorithm better than
|
||
the brute-force intersection of everything. The renderer even builds an
|
||
acceleration data structure! Despite the double precision and the
|
||
single-threadedness, it still runs at about 0.5 million rays per second on the
|
||
author’s machine.</li>
|
||
<li>Pause and resume: Can’t run <code>./hou</code> overnight? No problem! You can kill and
|
||
resume a rendering session whenever you want. The renderer automatically saves
|
||
the progress every 16 samples and resumes where it’s left off when restarted.
|
||
Also, each scene/parameter combination gets a different saved session so you
|
||
don’t have to worry about conflicts.</li>
|
||
</ul>
|
||
<h3 id="abuse-of-the-rules">Abuse of the rules</h3>
|
||
<ul>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/hou.c">hou.c</a> uses compression to get around the size limit. The compression
|
||
fully complies with the rules and the guidelines (at least the portion that
|
||
shows up in <code>grep</code> “size limit”). Please see the <a href="#self-imposed-restrictions">Self-imposed
|
||
restrictions</a> section below for more details.</li>
|
||
<li><code>hou</code> does not terminate (as suggested by the second line of rule 6).</li>
|
||
</ul>
|
||
<h3 id="self-imposed-restrictions">Self-imposed restrictions</h3>
|
||
<ul>
|
||
<li>The building process does not involve any OS tool beyond <code>cc(1)</code> and
|
||
<code>make(1)</code>. No <code>gzip(1)</code> compression! <code>a.c.gz</code> doesn’t fit in 2053 bytes, anyway.</li>
|
||
<li>Neither <a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/hou.c">hou.c</a> nor <code>a.c</code> (the <em>real</em> decompressed source) uses
|
||
<code>#define</code> (or <code>cc -D</code>) at all.</li>
|
||
<li>The source code is not required at runtime.</li>
|
||
<li><code>a.c</code> does not drop optional features to reduce size. There are pure
|
||
optimization code that can be dropped without affecting the converged output
|
||
(only affecting the ray tracing speed / convergence rate). All files are
|
||
properly <code>fopen()</code>ed with <code>"rb"</code> / <code>"wb"</code> for Windows compatibility. The PPM
|
||
header has a comment line for non-standard-compliant viewers (specifically, my
|
||
old HDRShop 1.0). And there is a nice text message saying “please wait…”.
|
||
Despite the messy look, <code>a.c</code> and <a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/hou.c">hou.c</a> compile warning-free
|
||
(<a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/hou.c">hou.c</a> even wastes 18 bytes on <code>#include<stdio.h></code> just for <code>putchar(3)</code>).
|
||
<code>a.c</code> compiles mostly clean in the C99/ANSI modes of clang and gcc (with:</li>
|
||
</ul>
|
||
<pre><code> -Wall --pedantic</code></pre>
|
||
<p>The only warning generated is a pedantic one: <code>"string constant too long"</code>.</p>
|
||
<h3 id="comments-and-why-obfuscated">Comments and why obfuscated</h3>
|
||
<ul>
|
||
<li>Both the compression and the rendering use mathematically involved algorithms.
|
||
Understanding the C doesn’t help much if one isn’t familiar with the math.</li>
|
||
<li>Modern renderers provide shader access to just about any internal state. This
|
||
one follows suit and reuses the same shader-accessible array for all important
|
||
internal states.</li>
|
||
<li>Infinity and NaN (not-a-number) are used during normal course of execution.</li>
|
||
<li>Previous image-generating entries may take care to hide the “IOCCC” string in
|
||
the code, but they leave the text clear in the <em>result</em>. This entry takes it
|
||
further and obfuscates the output image as well. Can you find the text in the
|
||
image? Hint: look up.</li>
|
||
<li><code>a.c</code> leaves all shaders in plain text, but the plain text shader code can’t
|
||
be taken for its face value; the arithmetic rules subtly diverge from our common
|
||
sense.</li>
|
||
<li><code>a.c</code> is less portable than <a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/hou.c">hou.c</a> itself. <a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/hou.c">hou.c</a> only depends
|
||
on ASCII and should run just fine on 16-bit, small memory, or
|
||
floating-point-incapable machines. <code>a.c</code>, while still reasonably portable, is
|
||
quite memory consuming, requires IEEE754-compliant <code>double</code>, and assumes <code>int</code> to be
|
||
32-bits.</li>
|
||
<li>Though technically endian-dependent, <code>a.c</code> remains portable providing that one
|
||
doesn’t copy saved sessions across different endianness.</li>
|
||
</ul>
|
||
<h3 id="notice-to-those-who-wish-for-a-greater-challenge">NOTICE to those who wish for a greater challenge:</h3>
|
||
<p><strong>If you want a greater challenge, don’t read any further</strong>:
|
||
just try to understand the program via the source.</p>
|
||
<p>If you get stuck, come back and read below for additional hints and information.</p>
|
||
<h3 id="how-this-entry-works">How this entry works:</h3>
|
||
<pre><code> 3225 3225 3225 9 9 3225 3225
|
||
1 1 1 1 1 1 1 1 1 1
|
||
4225 1226 1 1 1 1 1222 1226
|
||
1 1 1 1 1 1 1 1 1
|
||
4226 1 4226 8 4222 4226 1 1</code></pre>
|
||
<p>The program consists of a recursive-descent interpreter, a <code>3DDDA</code> (3D Discrete
|
||
Differential Analysis) ray tracer, a <code>PSSMLT</code> (Primary Sample Space Metropolis
|
||
Light Transport) light path sampler, all squeezed into the size limit using a
|
||
<code>PPM</code> compressor (Prediction by Partial Matching, and yes, the output format is
|
||
chosen for the pun..).</p>
|
||
<p><code>PSSMLT</code> uses the Metropolis-Hasting algorithm to sample a 32D unit hypercube.
|
||
Each point in the hypercube is interpreted as a sequence of random numbers, and
|
||
is sent to a path tracer to generate a light path. The point’s
|
||
Metropolis-Hasting energy is then defined as the corresponding path’s
|
||
contribution value to the final image. Since each path is sampled with a
|
||
probability proportional to its energy, the sample distribution directly
|
||
corresponds to the final image, which can then be produced as a simple per-pixel
|
||
histogram of all generated paths. The robustness comes from a state mutation
|
||
strategy that actively tries to explore the neighborhood of high energy peaks
|
||
(e.g., paths that happen to hit the light source in
|
||
<a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/otherroom.scene">otherroom.scene</a> file).
|
||
In addition, a rudimentary form of lens
|
||
path stratification is added to balance the attention each pixel receives. The
|
||
Metropolis-Hasting process completely avoids the tell-tale pixel sampling loop
|
||
required in most other image generation methods.</p>
|
||
<p>The <code>3DDDA</code> tracer is chosen for scalability: its performance doesn’t get much
|
||
worse as scene complexity increases. Another benefit is that with the <code>DDA</code> code
|
||
in place one can naturally use hierarchical grids as an acceleration structure.
|
||
The downside, of course, is that the setup involves quite a few divisions, which
|
||
naturally turns into divisions-by-zero. Fortunately, the IEEE754 standard has a
|
||
nice set of rules just for this purpose and the arithmetics are organized in a
|
||
specific way to take advantage of this. The shader interpreter component is
|
||
relatively straightforward, just an expression evaluator stripped to the bare
|
||
minimum – it doesn’t even support numerical constants natively. A final little
|
||
bit is a just-good-enough PRNG (Pseudo Random Number Generator) to replace the
|
||
low precision Windows <code>rand()</code> and the non-C99 Unix <code>drand48(3)</code>. An overnight
|
||
session would run through its short period many times, but that doesn’t
|
||
necessarily map to the same set of paths in <code>PSSMLT</code>. After all,
|
||
Metropolis-Hasting used an even worse PRNG in their 1953 paper.</p>
|
||
<p>The <code>PPM</code> compressor uses statically weighted fixed order contexts with an
|
||
arithmetic encoder tweaked for <a href="https://github.com/ioccc-src/winner/blob/master/2013/iocccsize.c">iocccsize.c</a>. The encoder emits octet-space pairs
|
||
where each octet encodes ~6.5 bits of information and each space encodes 2 bits
|
||
(thanks to the generous definition of “space” in <a href="https://github.com/ioccc-src/winner/blob/master/2013/iocccsize.c">iocccsize.c</a> code).
|
||
The compressor
|
||
actively shuffles the variable names around until the compressed string happens
|
||
to contain enough <code>{};</code>s to pass the final <a href="https://github.com/ioccc-src/winner/blob/master/2013/iocccsize.c">iocccsize.c</a> test.
|
||
There are a few other tweaks:</p>
|
||
<ul>
|
||
<li><p>The <code>PPM</code> model uses mostly whitespace characters for weights.</p></li>
|
||
<li><p>The encoder never emits <code>'"'</code> and <code>'\\'</code>.</p></li>
|
||
<li><p>The decoder uses an O(n^2) algorithm to avoid the gigabytes-sized hash table
|
||
frequently found in other <code>PPM</code> implementations.</p></li>
|
||
</ul>
|
||
<!--
|
||
|
||
Copyright © 1984-2024 by Landon Curt Noll. All Rights Reserved.
|
||
|
||
You are free to share and adapt this file under the terms of this license:
|
||
|
||
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
|
||
|
||
For more information, see:
|
||
|
||
https://creativecommons.org/licenses/by-sa/4.0/
|
||
|
||
-->
|
||
<!-- AFTER: last line of markdown file: 2013/hou/README.md -->
|
||
|
||
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|
||
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|
||
|
||
<!-- START: this line starts content generated by: bin/output-index-inventory.sh -->
|
||
|
||
<div id="inventory">
|
||
<h1 id="inventory-for-2013hou">Inventory for 2013/hou</h1>
|
||
</div>
|
||
<h2 id="primary-files">Primary files</h2>
|
||
<ul>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/hou.c">hou.c</a> - entry source code</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/Makefile">Makefile</a> - entry Makefile</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/hou.orig.c">hou.orig.c</a> - original source code</li>
|
||
<li><a href="doc/example.html">doc/example.html</a> - scene format documentation</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/old_default.scene">old_default.scene</a> - sample input</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/otherroom.scene">otherroom.scene</a> - sample input</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/try.sh">try.sh</a> - script to try entry</li>
|
||
<li><a href="luna.jpg">luna.jpg</a> - sample image input file</li>
|
||
<li><a href="old_default.jpg">old_default.jpg</a> - sample image input file</li>
|
||
<li><a href="otherroom.jpg">otherroom.jpg</a> - sample image input file</li>
|
||
</ul>
|
||
<h2 id="secondary-files">Secondary files</h2>
|
||
<ul>
|
||
<li><a href="2013_hou.tar.bz2">2013_hou.tar.bz2</a> - download entry tarball</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/README.md">README.md</a> - markdown source for this web page</li>
|
||
<li><a href="doc/camera.png">doc/camera.png</a> - documentation support image</li>
|
||
<li><a href="doc/cosine.png">doc/cosine.png</a> - documentation support image</li>
|
||
<li><a href="doc/draft.png">doc/draft.png</a> - documentation support image</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/doc/example.md">doc/example.md</a> - markdown source for doc/example.html</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/.entry.json">.entry.json</a> - entry summary and manifest in JSON</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/.gitignore">.gitignore</a> - list of files that should not be committed under git</li>
|
||
<li><a href="https://github.com/ioccc-src/winner/blob/master/2013/hou/.path">.path</a> - directory path from top level directory</li>
|
||
<li><a href="index.html">index.html</a> - this web page</li>
|
||
</ul>
|
||
<hr style="width:10%;text-align:left;margin-left:0">
|
||
<h4>
|
||
Jump to: <a href="#">top</a>
|
||
</h4>
|
||
|
||
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|
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||
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|
||
|
||
</div>
|
||
|
||
<!-- END: this line ends content from: inc/after-content.default.html -->
|
||
<!-- START: this line starts content from: inc/footer.inventory.html -->
|
||
|
||
<!--
|
||
|
||
Copyright © 1984-2025 by Landon Curt Noll. All Rights Reserved.
|
||
|
||
You are free to share and adapt this file under the terms of this license:
|
||
|
||
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
|
||
|
||
For more information, see:
|
||
|
||
https://creativecommons.org/licenses/by-sa/4.0/
|
||
|
||
-->
|
||
|
||
<div class="footer">
|
||
|
||
<div id="copyright"><h3>Copyright © 1984-2025 by Landon Curt Noll:
|
||
<a href="https://creativecommons.org/faq/#what-does-some-rights-reserved-mean"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">Some Rights Reserved</a></h3>
|
||
<p>
|
||
This work is <b>licensed by Landon Curt Noll</b> under
|
||
<b><a href="https://creativecommons.org/licenses/by-sa/4.0/?ref=chooser-v1"
|
||
target="_blank"
|
||
rel="license noopener noreferrer"
|
||
style="display:inline-block;">CC BY-SA 4.0</a></b>.
|
||
<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
|
||
src="../../png/cc.png"
|
||
alt="cc inside circle symbol">
|
||
<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
|
||
src="../../png/by.png"
|
||
alt="person inside circle symbol">
|
||
<img style="height:22px!important;margin-left:3px;vertical-align:text-bottom;"
|
||
src="../../png/sa.png"
|
||
alt="arrow looping back on itself inside circle symbol"><br>
|
||
You should <b>carefully review</b> the
|
||
<b><a href="https://creativecommons.org/licenses/by-sa/4.0/legalcode.en"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">CC BY-SA 4.0 LEGAL CODE</a></b>
|
||
before using the licensed material.<br>
|
||
You may wish to review the
|
||
<b><a href="../../license.html"
|
||
target="_blank"
|
||
rel="license noopener noreferrer">highlights of some of the key features and terms</a></b>
|
||
of <b>CC BY-SA 4.0</b>.<br>
|
||
</p>
|
||
</div>
|
||
|
||
<div id="coda"><h3>Coda</h3>
|
||
<p>
|
||
<a href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fwww.ioccc.org%2F2013%2Fhou%2Findex.html" rel="nofollow">Nu HTML check this web page</a><br>
|
||
<a href="#top">Jump to top</a> <a href="#content">Jump to Content</a> <a href="#inventory">Jump to Inventory</a><br>
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|
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