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597 lines
22 KiB
HTML
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22 KiB
HTML
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<meta charset="utf-8">
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<title>The International Obfuscated C Code Contest</title>
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<meta name="description" content="example.md for 2013/hou">
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<div class="header">
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<img src="../../../png/ioccc.png" alt="IOCCC image by Matt Zucker" width=300 height=110>
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<h1>The International Obfuscated C Code Contest</h1>
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<h2>example.md for 2013/hou</h2>
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<a href="../../../bugs.html">Bugs & (mis)features</a>
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<a href="../../../faq.html#fix_an_entry">Fixing IOCCC entries</a>
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<a href="../../../faq.html#fix_web_site">Fixing the web site</a>
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<a href="../../../faq.html#fix_author">Fixing author info</a>
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<a href="../../../judges.html">The IOCCC Judges</a>
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<h1 id="scene-format-documentation">Scene format documentation</h1>
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<p>The file must be encoded in UTF-8 as the BOF marker indicates.</p>
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<p>You can directly feed it to the renderer. If you’re wondering about what the following code block does, that’s why:)</p>
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<pre><code>@|?|?z#
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@|||?z&
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>?Sedvf
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??Tdeu#
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>>Tdeui
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??Tdmmf
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??[[euf
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?}?Oq}e
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?}?Oqqf
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v}?|q}e
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v}?|qqf
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?Sj|?{f
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?Tjk?{e
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FF?Oqq$
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RR?Oqq$
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^^?Oqq$
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jj?Oqq$
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vv?|qq$
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IOBMqqe
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U]BMqqe
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aiBMqqe
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muBMqqe
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EEEJpp%
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QQEJpp%
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]]EJpp%
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iiEJpp%
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uuEJpp%
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ZnY|{|e
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[mZ|\{\{#
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[mZ|||f
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kkdr\{\{\%
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lkdr\{\{></code></pre>
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<h2 id="basic-structure">Basic structure</h2>
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<p>A scene file begins with arbitrary binary data, followed by several shader
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functions.</p>
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<p>Shader functions are declared using a one-character name followed by a <code>]</code>
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character. There are some special function names, which will be explained below.</p>
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<p>The language used to write shader functions is very simple. Basically, you write
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a sequence of assignment statements like this:</p>
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<pre><code>A=A+D
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B=B+E</code></pre>
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<p>Namely, you write a one-character variable name, an equal sign (<code>=</code>), followed
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by an expression (made of operators and one-character variable names, of
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course).</p>
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<h2 id="expressions">Expressions</h2>
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<p>The shader language supports seven operators, listed highest priority first:</p>
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<pre><code>*/+-<#:</code></pre>
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<p><code>*/+-<</code> each mean what they mean in C, but the priority part is a bit different.
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Basically, <code>*</code> has higher priority than <code>/</code>, so <code>A/4*4</code> actually computes
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<code>A/(4*4)</code>. And you can’t write <code>(A/4)*4</code> – brackets are not supported. As an
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advice, keep your expressions simple :) If you really needs to write something
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like <code>C=(A/4)*4</code>, write instead:</p>
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<pre><code>B=A/4+
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C=B*4</code></pre>
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<p>The <code>#</code> operator acts somewhat like the C <code>?:</code>. It returns one of its two
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operands based on, what else, the value of variable <code>#</code>. When <code>#</code> is true, <code>#</code>
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returns its second operand.</p>
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<p>The <code>:</code> operator calls built-in functions. The first operand is the function id and the second is the parameter. Here is a list of functions:</p>
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<pre><code>0:x = the x-th byte of the scene file
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1:x = sin(x*PI)
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2:x = atan2(x,#)/PI
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3:x = sqrt(max(x,0))
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4:x = floor(x)
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5:x = the next number in the (allegedly random) number sequence, can't be called in volume shaders
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6:x = value of the variable (char)(120+x)
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7:x = write #'s value to the variable (char)(120+x)</code></pre>
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<p>Contrary to popular belief, the language itself doesn’t support numerical
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constants. Any character sitting between operators is a variable. When you see
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1/2, it’s in fact dividing the variable 1’s value by the variable 2’s value. For
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everyone’s convenience, though, in the beginning every variable is initialized
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to its ASCII code minus 48. As long as you don’t write something like <code>3=1+1</code>,
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you can use single digit numbers as, well, single digit numbers. If you need
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something like <code>1920</code> or <code>0.73</code>, you need to compute it yourself. And yes, all
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variables store floating point values.</p>
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<p>If a character appears as the first character of any <code>argv</code>, it goes to zero.
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This includes the scene filename. If you name your scene <code>1.scene</code>, well, good
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luck with <code>1=0</code>!</p>
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<p>You can terminate a statement using any character that isn’t an operator, be it
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<code>\n</code> or <code>;</code>. But you must put in one and only one character. Put in two (e.g.
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the Windows <code>\r\n</code>), and it terminates your function. Also, the first statement
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must begin immediately after <code>]</code>.</p>
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<p>When a function terminates, the interpreter calls the next function specified by
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variable <code>R</code>. If you want to call function <code>n</code>, just write somewhere:</p>
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<pre><code>R=n</code></pre>
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<p>providing you have left <code>n</code> at its initial value. If you want to actually return
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to the renderer, put in <code>R=0</code>.</p>
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<p>As you may have noticed, you can put in all kinds of stuff between functions,
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like this comment.</p>
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<h2 id="how-the-____-do-i-render-an-image-with-shaders">How the ____ do I render an image with shaders?</h2>
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<p>Basically, you define a geometry using volume shaders, define a camera using a
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camera shader, and define light sources and surface reflectance properties using
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material shaders.</p>
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<table>
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<tbody>
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<tr class="odd">
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<td style="text-align: left;">Continue to the comments before function A</td>
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</tr>
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</tbody>
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</table>
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<pre><code>//As an (optional) assignment, figure out what function 'n' does. And why there is a plus sign at every EOL except the last.
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n]#=1+
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x=X+1/2+
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d=0:U;d=d-n;U=U+1;A=d<x;#=#*A+
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d=0:U;d=d-n;U=U+1;A=x<d+1;#=#*A+
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x=Y+1/2+
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d=0:U;d=d-n;U=U+1;A=d<x;#=#*A+
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d=0:U;d=d-n;U=U+1;A=x<d+1;#=#*A+
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x=Z+1/2+
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d=0:U;d=d-n;U=U+1;A=d<x;#=#*A+
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d=0:U;d=d-n;U=U+1;A=x<d+1;#=#*A+
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d=0:U;d=d-n;U=U+1+
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U=U+2+
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C=C#d+3*9+
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#=d+
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R=0#n</code></pre>
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<hr />
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<p>The function <code>A</code> initializes global settings:</p>
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<pre><code>G -- Image width, in pixels
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H -- Image height, in pixels
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I -- Perturbation probability
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J -- Camera ray stratification probability</code></pre>
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<p>If you have used a MLT renderer before, you probably know what <code>I</code> and <code>J</code> does.
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If you don’t, well, use the same value as the default scene. Everything
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converges just fine under suboptimal settings, just a little slower. Generally,
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use a higher value for <code>I</code> if your scene is primarily illuminated by some
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indirect source.</p>
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<p><code>A</code> also serves as the geometry shader for volume 0. The scene geometry is made
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of up to 32 volumes, each with 64x64x64 cells. The volume 0 is the ‘top level’
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volume where the camera goes. Each cell of a volume can be empty, filled with a
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material, or another volume. The roundish characters in
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<a href="../old_default.scene">old_default.scene</a> and the carpet on the floor in this
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file are examples where a cell is defined to another volume. Materials will be
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explained later.</p>
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<p>The volume shader for the i-th volume is named as the (i+1)-th capital letter.
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Each volume shader is invoked once for each cell. The cell coordinates (0..63)
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are given as inputs in variable <code>x</code>,<code>y</code>,<code>z</code>, and you’re supposed to return the
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cell content in variable <code>C</code>. To fill it with material <code>i</code>, return <code>64+i</code> in
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<code>C</code>. To fill it with volume <code>i</code>, well, return <code>i</code>. To leave it empty, return
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<code>C=0</code>.</p>
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<p>Before starting to build a scene, it’s better to have a draft sketch handy
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first. Something like <img src="draft.png" alt="Draft sketch" />. Sometimes it’s hard to
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imagine where something should go without the sketch. And you don’t have to
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stick to your sketch :)</p>
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<p>What motivated my default scene: it was the full moon’s day (a national holiday)
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in China and my parents were planning to renovate their apartment. I rendered
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the image to tell my mom how ridiculous her starry-sky wall paper would look
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like if she used it on every single wall. She ends up using it on just one wall,
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the one facing my bed, to thank me for the effort.</p>
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<table>
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<tbody>
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<tr class="odd">
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<td style="text-align: left;">Continue to the comments before function a</td>
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</tr>
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</tbody>
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</table>
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<pre><code>//As a bonus, find out what the first line does
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A]#=#-#;"=7:0-p+^;#="+
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R=n+
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G=p*:+
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#=0<B+
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G=G*2#G+
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H=G*3/4+
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I=4/5+
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J=1/2+
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C=p+1+
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U=w+w+w</code></pre>
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<hr />
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<p>The function <code>a</code> is the camera shader, which, well, generates the camera ray.
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It’s supposed to return the ray in variables <code>UVWXYZ</code> and <code>ABCDEF</code> (that may
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sound like a lot of variables, but it really isn’t that much).</p>
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<p>Here comes some subtlety of <code>PSSMLT</code> (Primary Sample Space Metropolis Light
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Transport, or Kelemen-style MLT). Basically, a <code>PSSMLT</code> renderer gives you an
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(allegedly random) number sequence, and you compute a color out of it. This is
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usually done by generating and tracing rays out of those random numbers. The
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renderer would assemble the colors into an image.</p>
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<p>Remember the function <code>5</code>? Here it comes. The first two “random” numbers have
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special meaning and must specify a point on the image plane <code>[0,1)x[0,1)</code>.
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You’re supposed to transform the image plane to the 3D space, choose a point for
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the camera, and shoot a ray from the camera point to the image plane point, see
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<img src="camera.png" alt="Camera convention" />. The camera point goes to <code>(U,V,W)</code>, and the
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ray direction vector (image plane point - camera point) is <code>(X,Y,Z)</code>. For the
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coordinate space, volume 0 is scaled up 64x here to <code>(0,0,0)-(4096,4096,4096)</code>.</p>
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<p>For a basic camera shader example, check <a href="../otherroom.scene">otherroom.scene</a>.</p>
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<p>If any ray goes out of volume 0, the renderer crashes. Make sure it doesn’t
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happen. Wall up everything.</p>
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<p>Variables <code>ABCDEF</code> control the color returned from the ray. They will be
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explained in the material shaders part. For now, just put in:</p>
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<pre><code>A=0;B=0;C=0
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D=1;E=1;F=1</code></pre>
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<table>
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<tbody>
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<tr class="odd">
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<td style="text-align: left;">Continue to the comments before function 1</td>
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</tr>
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</tbody>
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</table>
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<pre><code>a]R=0+
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X=5:5+
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Y=5:5+
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X=X-1/2+
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Y=Y-1/2+
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x=5:5+
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y=5:5+
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x=x-1/2+
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y=y-1/2+
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x=x*8*7;y=y*8*7+
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X=X*G+
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Y=Y*H+
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Z=H*2/3+
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d=4*;+
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d=d*p/Z+
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X=x+X*d+
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Y=y+Y*d+
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Z=Z*d+
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U=p*p/2-p*2+x+
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V=p*p/2+p*1-y+
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W=p*8+
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A=0;B=0;C=0+
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D=1;E=1;F=1</code></pre>
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||
<hr />
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||
<p>The numbered functions define materials, i.e., surface reflectance properties.
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As the name suggests, the shader simulates ray-surface interaction. It’s done by
|
||
updating <code>UVWXYZABCDEF</code>, of course.</p>
|
||
<p><code>ABCDEF</code> define colors. <code>(A,B,C)</code> is the RGB irradiance ultimately returned to
|
||
the renderer, and <code>(D,E,F)</code> maintain the cumulative RGB reflectance of the
|
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current ray path. This may sound confusing, but basically, if the surface is a
|
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light source, you accumulate the current path reflectance <code>(D,E,F)</code>, multiplied
|
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by the light strength, to <code>(A,B,C)</code>. See shader 6 for an example.</p>
|
||
<p>If you want a colored surface, use its color to modulate <code>(D,E,F)</code>, i.e.
|
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<code>D=D*red;E=E*green;F=F*blue</code>, easy as that. To get some texturing, compute the
|
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color procedurally or look up a binary table.</p>
|
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<p>There’s something subtle about colors. To go along with the trend, the renderer
|
||
follows the practice of linear rendering with a gamma of <code>2</code>. Stripping the
|
||
fancy jargon, that basically means after picking a color in your favorite image
|
||
editing program, you need to convert the RGB values from 0..255 to 0..1, and
|
||
then put here its <em>square</em>. Only after squaring you get your real, lively color
|
||
in the output image, as opposed to something dull and gray. You need to do the
|
||
same if you use a RGB texture. And yes, that is the what the second <code>sqrt(3)</code> in
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<a href="../a.c">a.c</a> is for.</p>
|
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<p>Going beyond colors, to define a shiny or dull surface one needs more maths, and
|
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optics. The jargon for this is <code>BRDF</code> (Bidirectional Reflectance Distribution
|
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Function) importance sampling. Let’s continue to function <code>o</code>.</p>
|
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<table>
|
||
<tbody>
|
||
<tr class="odd">
|
||
<td style="text-align: left;">Continue to the comments before function o</td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<pre><code>//This function computes the starred wallpaper
|
||
//Original color: 0.36 0.714285 0.8
|
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1]R=o+
|
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d=p*6+
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x=U+W+
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x=4:x/d+
|
||
z=4:V/d+
|
||
#=3*x-4*z+
|
||
y=4:#/5+
|
||
#=#-y*5+
|
||
y=1#0+
|
||
x=x*d+d/2-U+W+
|
||
z=z*d+d/2-V+
|
||
r=3:x*x+z*z+
|
||
#=z+
|
||
u=2:x+
|
||
d=1:u*5+
|
||
d=d*d*d+3/2+
|
||
d=d*p+
|
||
#=r<d+
|
||
#=#*y+
|
||
d=2/5#I+
|
||
D=D*d+
|
||
E=E*4/7+
|
||
d=I#2/5+
|
||
F=F*d</code></pre>
|
||
<hr />
|
||
<p>Function <code>o</code> defines a diffuse (that is, dull) surface. To define reflectance
|
||
properties like this, one needs to sample an outgoing ray direction, based on
|
||
the incoming direction and the surface normal. It’s called importance sampling,
|
||
because here the probability of each outgoing direction has to be proportional
|
||
to the reflected light strength (i.e., the <code>BRDF</code>) on that direction. For a
|
||
diffuse surface, sample the upper hemisphere with a probability proportional to
|
||
the cosine of the outgoing angle, see <img src="cosine.png" alt="Cosine sampling" />.</p>
|
||
<p>The incoming direction is in <code>(X,Y,Z)</code> and the hit point is <code>(U,V,W)</code>. The
|
||
outgoing direction is returned in, where else, <code>(X,Y,Z)</code>.</p>
|
||
<p>The surface normal is provided in variables <code>S</code> and <code>T</code>. Since the geometry is
|
||
defined as a bunch of cube-shaped cells, there are only 6 possible normals:
|
||
<code>(±1,0,0) (0,±1,0) (0,0,±1)</code>. Here <code>S</code> is the sign and <code>T</code> is the dimension. If
|
||
you get <code>S=-1</code> and <code>T=1</code>, the normal is <code>(0,-1,0)</code>.</p>
|
||
<p>If you don’t want to redo all the math yourself… this file provides a few simple shader functions:</p>
|
||
<pre><code>o -- Diffuse surface. Do the color thing your self and call R=o
|
||
5 -- Perfect mirror.
|
||
f -- Surface with a Fresnel term. Basically, it resembles a polished surface made from a dielectric material.</code></pre>
|
||
<p>For something more complex like a fluffy carpet, well, you could use a volume to
|
||
directly model the
|
||
<a href="https://en.wikipedia.org/wiki/Mesoscopic_physics">mesoscopic</a> detail. Shader
|
||
<code>D</code> in this file produces a bunch of dense, tiny spikes to simulate a fluffy
|
||
appearance.</p>
|
||
<table>
|
||
<tbody>
|
||
<tr class="odd">
|
||
<td style="text-align: left;">Continue to the EOF</td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<pre><code>//diffuse ray generation
|
||
o]R=0+
|
||
u=5:5+
|
||
v=5:5+
|
||
v=v*2+
|
||
r=3:u+
|
||
z=1:v+
|
||
y=1:1/2+v+
|
||
z=z*r+
|
||
y=y*r+
|
||
x=3:1-u+
|
||
x=0-x*S+
|
||
X=6:T+
|
||
w=x;x=z;z=y;y=w+
|
||
Y=6:T+
|
||
w=x;x=z;z=y;y=w+
|
||
Z=6:T
|
||
|
||
//reflector
|
||
5]R=0+
|
||
x=1;y=1;z=1+
|
||
#=0-1+
|
||
#=7:T+
|
||
X=x*X;Y=y*Y;Z=z*Z
|
||
|
||
//approximate Fresnel, works better than the real thing when you don't want to tweak the IOR
|
||
f]x=X;y=Y;z=Z+
|
||
r=3:x*x+z*z+y*y+
|
||
d=6:T+
|
||
d=1-d*S/r+
|
||
d=d*d*d+
|
||
#=5:5+
|
||
#=d<#+
|
||
R=5#o+
|
||
d=d#1-d+
|
||
u=1#u+
|
||
v=1#v+
|
||
w=1#w+
|
||
D=D*d*u+
|
||
E=E*d*v+
|
||
F=F*d*w
|
||
|
||
//the handles
|
||
B]R=0+
|
||
#=X<8*3+
|
||
C=3#0
|
||
|
||
C]R=0+
|
||
#=X<8*4+
|
||
C=0#4
|
||
|
||
//red-Fresnel
|
||
2]R=f+
|
||
u=1/2;v=1/9;w=v
|
||
|
||
//white-Fresnel and the full moon
|
||
3]R=f+
|
||
u=7*9/p;v=u;w=v+
|
||
x=3*:+8+
|
||
z=U-x*p+p/2+
|
||
x=V-x*p-p/2+
|
||
r=3:x*x+z*z+
|
||
#=4<r/p+
|
||
D=D*I#D+
|
||
E=E*4/7#E+
|
||
F=F*2/5#F+
|
||
d=1/5#0+
|
||
A=A+D*d+
|
||
B=B+E*d+
|
||
C=C+F*d
|
||
|
||
//handle
|
||
4]R=5+
|
||
D=D*I;E=E*4/7;F=F*2/5
|
||
|
||
//light from the window
|
||
6]R=0+
|
||
#=P+
|
||
d=2#8*2+
|
||
A=A+D*d+
|
||
B=B+E*d+
|
||
C=C+F*d*I+
|
||
P=9
|
||
|
||
//carpet
|
||
7]R=o+
|
||
D=D/7+
|
||
E=E/3+
|
||
F=F/7
|
||
|
||
D]R=0+
|
||
#=8<Y+
|
||
C=0#3+
|
||
#=4:3*X-4*Z+
|
||
y=4:#/7+
|
||
#=#-y*7+
|
||
C=7#C</code></pre>
|
||
<hr />
|
||
<p>The last line, well, is the output filename. Just remember to throw in two <code>]</code>s
|
||
and don’t put a newline after it.</p>
|
||
<pre><code>]]example.ppm</code></pre>
|
||
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