602 words ~ 3-6 mins — Mathieu 'p01' Henri on August 6th, 2017


VOLTRA: Grinding the Universe, a gritty JavaScript demo, winner of the 1024 bytes demo competition at the Assembly 2017.

The Assembly is a 25 years old demoscene event with the most anticipated 1kb, 4kb, 64kb and 256mb demo competitions. And I can not be more excited of winning the 1kb competition again after winning 2 years ago with BLCK4777 and getting 2nd place last year with ASTRA.

Grinding the Universe in 1024 bytes

With VOLTRA, I wanted to do something gritty. Extremely gritty. Something with a soundtrack out of this world, vocals ( yes! vocals in a 1kb demo ) and some visuals inspired by PETSCII and CGA graphics with a modern twist of 3D and post processing.

Here is a video capture of the final result, just in case.

Technical breakdown

The rules of the Assembly, and other demoscene competitions, is that the entry must be released as a single file, ready to run from file system. For the 1kb competition, the size limit is 1024 bytes. Since the entry must run from file system we can not use Gzip. To get the most we must somehow compress our entry and fit the compressed data and the decompressor code into 1024 bytes.

Minified code

The minified code of VOLTRA is 1345 bytes long.

c.style.width=c.style.height=`100%`,c.style.position=`fixed`,document.body.style.background=`radial-gradient(#023,#000)`,document.body.style.font=`0 a`;for(x=0;x<64;x++)c.width=c.height=12,b.shadowBlur=4,b.fillStyle=b.shadowColor=x%11?`#cff`:`#f26`,b.globalAlpha/=x<40?1:4,b.fillText(`  V0LTRA ][ R1BB0N  `[x]||S(9584+x),2,8),c[x]=b.createPattern(c,`repeat`);c.height=384,g=new AudioContext,p=g.createScriptProcessor(2048,c.style.top=c.style.left=a=m=0,1),p.connect(g.destination),p.onaudioprocess=o=>{for(u=o.outputBuffer.getChannelData(0),d=Math.sin(m/32),e=Math.cos(4*Math.cos(4*d)),f=Math.sin(4*Math.cos(4*d)),c.width=12*64,c.style.transform=`perspective(64vh)rotate3d(0,1,${f},${m/8}deg)scale(${1+(m/96)**64})`;a/64+64<8*m;b[i+64]=1&(-4&d*64)>>(4*b[i-1]+b[i]*2+b[i++])^1.01*Math.random())i=a++%2048;for(i=y=0;y<32;y++)for(x=0;x<64;x++)m+=1/g.sampleRate,j=2^y/5|1^x/20?(n=x/8*e-4*e-y/8*f+4*f+u[i]/4,o=x/8*f-4*f+y/8*e-4*e+16*d-8,n=0<o&[n%o,n&o+e*m,m+b[384|n+(o<<6)],n%o][3&m/24],b[i]|n&&(y^x&m)%16+40-20*n):12==y&&x<4*m?x-20:0,j&&b.fillRect(12*x,12*y,12,12,b.fillStyle=c[j^1.01*Math.random()]),u[i++]=(j/8+`9584`[3&m/24]*8)*m%1*d*d;b.globalAlpha/=x<40?1:4,b.drawImage(c,12*24,12*12,12,12,0,12*12,12*64,12),b.drawImage(c,12*12,12*24,12*3,24,0,0,12*64,384),3&m/24&&(h=speechSynthesis.speak(h,h.rate=0))};h=new SpeechSynthesisUtterance(`voltra`)

It assumes the following setup which takes another 81 bytes + some to load and run the minified code above.

<canvas id="c"></canvas><script>b=c.getContext`2d`;S=String.fromCharCode</script>

All in all, this about 1460 bytes of minified code that we'll have to compress down to 1024 bytes of self extracting code.

Compression & PNG bootstrapping

The final file, VOLTRA.htm, is a polyglot file which is both a PNG image and an HTML page with a bit Javascript that loads the file in an IMG element, draws the pixels in a CANVAS and treats them as the ASCII value of a long string of character which is finally evaluated. This way of bootstrapping a PNG image allows to ship a single file and to benefit from the compression ratio of PNG and ZLIB, and all the tooling that comes with it.

The code of the PNG bootstrapper takes 161 bytes.

<canvas id=c><img onload=b=c.getContext`2d`;S=String.fromCharCode;for(i=e='';t=b.getImageData(0,0,1,!b.drawImage(this,i--,0)).data[0];)e+=S(t);(1,eval)(e) src=#>

This means the PNG image must be no bigger than 1024 - 161 = 863 bytes after removing the IEND chunk. Taking into account the PNG header and various chunk headers, this leave a mere 818 bytes of DEFLATE stream for the code of our demo.

In other words: there really isn't much space to do something cool.

To be continued with the technical breakdown of the following topics...


Sprite sheet

Cellular automata


3D camera

Post processing


Speech Synthesis

Additional links