JS1K: Swarms

In the spirit of the demoscene, the JS1K competition is designed to make people push their boundaries. The competition requires entrants to write an interesting, appealing demo in JavaScript, using no more than 1024 characters (hence the name).

Of course, I had to have a shot at it. (See the result!) I decided to revisit one of my favourite toy projects: my swarms. What I came up with is this (linebreaks added for convenience):

[sourcecode language=”javascript”]a=Math,b=a.random,c=[],j=document.getElementById(“c”),k=j.getContext(“2d”),m=window,n=(W=m.innerWidth)/2,q=(H=m.innerHeight)/2,r=M=1;function s(o,p,u,v){k.fillStyle=o;k.beginPath();k.arc(p,u,v,0,a.PI*2,0);k.closePath();k.fill()}function t(o,p){for(g=40;g–;)if(!c[g]){c[g]={x:o||n,y:p||q,d:o?b()*4-2:0,e:p?b()*4-2:0,b:1,a:0,c:b()>.5};return}}with(j.style){position=”fixed”;top=left=0}j.width=W;j.height=H;for(f=40;f–;)c[f]=0;for(f=9;f–;)t(); m.setInterval(function(){k.fillStyle=”rgba(9,9,9,.2)”;k.fillRect(0,0,W,H);for(f=40;f–;)if(d=c[f])if(d.a>1E3)c[f]=0;else{l=d.a/1E3;h=l*7;d.d+=b()*.1*(n-d.x>1?1:n-d.x<-1?-1:n-d.x);d.e+=b()*.1*(q-d.y>1?1:q-d.y<-1?-1:q-d.y);d.x+=d.d;d.y+=d.e;d.a++;i=d.c?"rgba(49,153,255,":"rgba(255,49,166,";h=1-l;s(i+h+")",d.x,d.y,1+l*12);s(i+h/2+")",d.x,d.y,1+l*16);d.b&&d.b--;if(d.b==0&&d.a>250&&d.a<750&&b()>.9)for(g=40;g–&&!d.b;)if((e=c[g])&&e!=d&&e.a>=d.a){i=a.sqrt(d.x-e.x,d.y-e.y);if(i>-5&&i<5&&d.c!=e.c){t(d.x, d.y);d.b=e.b=10}}}r=n>W||n<0?-r:r;M=q>H||q<0?-M:M;n+=r;q+=M},40);[/sourcecode]You can see the submission here: http://js1k.com/demo/270. To reduce the size, I first coded tightly, ran the uncompressed code through Google’s Closure Compiler, then hand-tweaked the result to save a few more bytes. I’m quite pleased with the result! For the curious, the full, uncompressed, commented source is below:

[sourcecode language=”javascript”]/* SWARMS (v1.7)
* by Barry van Oudtshoorn (www.barryvan.com.au)
* A re-implementation of http://www.barryvan.com.au/demos/swarms/swarms.html,
* which in turn is a reimplementation of a Processing script that I wrote.
*
* Male and female particles move around a central point, gradually aging.
* When they reach maturity, they may interact with a particle of the opposite
* sex to spawn a new particle. As they grow old, they become larger and slower
* until they eventually die.
*
* Revisions (really, these version numbers are all but meaningless!)
* 1.0 (1023B)
* – Initial code.
* 1.5 (1017B)
* – Moved to Closure compiler to reduce size
* – Some slight tweaks to particle movement
* – Canvas now positioned to get rid of annoying border (try fullscreen!)
* 1.7 (1011B)
* – The swarm centre now moves around (simple bouncing). This allows the
* particles to pick up a bit more speed, and move in more interesting ways;
* where before they tended to just ‘bubble’ in the middle of the screen,
* the swarm, as an entity, now appears more fluid and organic.
* – Bugfix to spawning: particles now actually have to be near to each other
* in BOTH axes to spawn, and both particles have to be of suitable age. This
* prevents billions of particles from spawning from a single one.
* – Reduced the total number of particles for aesthetic reasons
* – Did some more “by-hand” optimisations after running it through the closure
* compiler, like removing global variable declarations when I’m not
* instantiating the variables there and then and removing the leading 0 on
* decimal values to conserve precious bytes. With each revision, despite
* adding functionality each time, the size is going down!
*
* Copyright 2010 Barry van Oudtshoorn.
*/

var z = function(a, b, c) { // Normalise a to between b and c
return (a / (c – b));
},
h = function(a, b, c) { // Limx a to between b and c
return (a > b ? b : (a < c ? c : a)); }, // I strip out all of the uninitialised declarations after compilation; // they're globals anyway. I know it's not stylish, but it saves bytes! r,s, // Particles that we're currently interested in i,j, // Iterators u,d, // Working variables m = Math, // Alias v = m.random, // Alias p = [], // The particles e = document.getElementById('c'), // The canvas element t = e.getContext('2d'), // The context n, // The normalised age of a particle Q = window, // Alias X = (W = Q.innerWidth)/2, // The swarm's COG Y = (H = Q.innerHeight)/2, N = M = 1, // The components of the velocity of the swarm's COG q = function(a, b, c, f) { // Draw a blob t.fillStyle = a; t.beginPath(); t.arc(b, c, f, 0, m.PI*2, 0); t.closePath(); t.fill(); },x = function() { // Global iterator //t.globalCompositeOperation = 'source-over'; // This is prettier, but "globalCompositeOperation" takes too many bytes! t.fillStyle = 'rgba(9,9,9,.2)'; t.fillRect(0,0,W,H); //t.globalCompositeOperation = 'lighter'; for (i = 40; i--;) { // Loop over all of the particles if (r = p[i]) { if (r.a > 1E3) {
p[i] = 0; // Kill off old particles; use 0 because it’s shorter than false, null, or using delete.
} else {
// Move the particle
n = z(r.a, 0, 1E3);
u = n * 7;
r.X += v() * .1 * h(X – r.x, 1, -1); // Update the particle’s velocity.
r.Y += v() * .1 * h(Y – r.y, 1, -1);
r.x += r.X; // Update the particle’s coordinates based on its velocity.
r.y += r.Y;
r.a++; // Increment the particle’s age

// Draw the particle

d = r.s ? ‘rgba(49,153,255,’ : ‘rgba(255,49,166,’; // The colour of the particle
u = 1 – n; // The opacity of the particle; n is the normalised age
q(d + u + ‘)’, r.x, r.y, 1 + n * 12); // Draw the primary particle blob
q(d + (u/2) + ‘)’, r.x, r.y, 1 + n * 16); // We draw a lighter, larger blob for a ‘glow’ effect

r.f && r.f–; // If we’ve spawned, decrement the cooldown.

if (r.f == 0 && r.a > 250 && r.a < 750 && v() > 0.9) { // If we’re the right age, check if we can spawn!
for (j = 40; j– && !r.f;) { // We have to loop over the particles again, and see if we’re close enough to spawn.
if ((s = p[j]) && s != r && s.a >= r.a) {
d = m.sqrt(r.x – s.x, r.y – s.y); // Two if statements to avoid this calculation if possible
if (d > -5 && d < 5 && r.s != s.s) { // Collision detection? What's that? y(r.x, r.y); // Spawn a new particle! r.f = s.f = 10; // Enforce the spawning cooldown } } } } } } } // Bounce the swarm's COG around the canvas N = (X > W || X < 0 ? -N : N); M = (Y > H || Y < 0 ? -M : M); X += N; Y += M; },// Spawn a new particle. If sx and sy are defined, they will be its initial // coordinates; otherwise, we just the COG. If sx and sy are defined, we also // give the particle a random velocity; this means that they're 'flung out' // from their parents; at startup, though, we want them all nicely bunched. y = function(sx,sy) { for (j = 40; j--;) { if (!p[j]) { p[j] = { x: sx || X, // The particle's coords y: sy || Y, X: sx ? v() * 4 - 2: 0, // The particles velocity Y: sy ? v() * 4 - 2 : 0, f: 1, // Cooldown after spawning a: 0, // The age of the particle s: v() > .5 // The sex of the particle
}
return;
}
}
};

// Make the canvas fill the entire screen
with (e.style) {
position = ‘fixed’;
top = left = 0;
}
e.width = W; // Set the canvas width and height
e.height = H;

for (i = 40; i–;) p[i] = 0; // Populate initial particles
for (i = 9; i–;) y(); // Spawn eight particles. A number < 10 saves a byte!Q.setInterval(x, 40); // Make it go. [/sourcecode]