A Pen By
Matei Copot
Pro

` ````
<canvas id=c></canvas>
```

` ````
canvas {
position: absolute;
top: 0;
left: 0;
}
```

` ````
var w = c.width = window.innerWidth,
h = c.height = window.innerHeight,
ctx = c.getContext( '2d' ),
opts = {
len: 20,
count: 50,
baseTime: 10,
addedTime: 10,
dieChance: .05,
spawnChance: 1,
sparkChance: .1,
sparkDist: 10,
sparkSize: 2,
color: 'hsl(hue,100%,light%)',
baseLight: 50,
addedLight: 10, // [50-10,50+10]
shadowToTimePropMult: 6,
baseLightInputMultiplier: .01,
addedLightInputMultiplier: .02,
cx: w / 2,
cy: h / 2,
repaintAlpha: .04,
hueChange: .1
},
tick = 0,
lines = [],
dieX = w / 2 / opts.len,
dieY = h / 2 / opts.len,
baseRad = Math.PI * 2 / 6;
ctx.fillStyle = 'black';
ctx.fillRect( 0, 0, w, h );
function loop() {
window.requestAnimationFrame( loop );
++tick;
ctx.globalCompositeOperation = 'source-over';
ctx.shadowBlur = 0;
ctx.fillStyle = 'rgba(0,0,0,alp)'.replace( 'alp', opts.repaintAlpha );
ctx.fillRect( 0, 0, w, h );
ctx.globalCompositeOperation = 'lighter';
if( lines.length < opts.count && Math.random() < opts.spawnChance )
lines.push( new Line );
lines.map( function( line ){ line.step(); } );
}
function Line(){
this.reset();
}
Line.prototype.reset = function(){
this.x = 0;
this.y = 0;
this.addedX = 0;
this.addedY = 0;
this.rad = 0;
this.lightInputMultiplier = opts.baseLightInputMultiplier + opts.addedLightInputMultiplier * Math.random();
this.color = opts.color.replace( 'hue', tick * opts.hueChange );
this.cumulativeTime = 0;
this.beginPhase();
}
Line.prototype.beginPhase = function(){
this.x += this.addedX;
this.y += this.addedY;
this.time = 0;
this.targetTime = ( opts.baseTime + opts.addedTime * Math.random() ) |0;
this.rad += baseRad * ( Math.random() < .5 ? 1 : -1 );
this.addedX = Math.cos( this.rad );
this.addedY = Math.sin( this.rad );
if( Math.random() < opts.dieChance || this.x > dieX || this.x < -dieX || this.y > dieY || this.y < -dieY )
this.reset();
}
Line.prototype.step = function(){
++this.time;
++this.cumulativeTime;
if( this.time >= this.targetTime )
this.beginPhase();
var prop = this.time / this.targetTime,
wave = Math.sin( prop * Math.PI / 2 ),
x = this.addedX * wave,
y = this.addedY * wave;
ctx.shadowBlur = prop * opts.shadowToTimePropMult;
ctx.fillStyle = ctx.shadowColor = this.color.replace( 'light', opts.baseLight + opts.addedLight * Math.sin( this.cumulativeTime * this.lightInputMultiplier ) );
ctx.fillRect( opts.cx + ( this.x + x ) * opts.len, opts.cy + ( this.y + y ) * opts.len, 2, 2 );
if( Math.random() < opts.sparkChance )
ctx.fillRect( opts.cx + ( this.x + x ) * opts.len + Math.random() * opts.sparkDist * ( Math.random() < .5 ? 1 : -1 ) - opts.sparkSize / 2, opts.cy + ( this.y + y ) * opts.len + Math.random() * opts.sparkDist * ( Math.random() < .5 ? 1 : -1 ) - opts.sparkSize / 2, opts.sparkSize, opts.sparkSize )
}
loop();
window.addEventListener( 'resize', function(){
w = c.width = window.innerWidth;
h = c.height = window.innerHeight;
ctx.fillStyle = 'black';
ctx.fillRect( 0, 0, w, h );
opts.cx = w / 2;
opts.cy = h / 2;
dieX = w / 2 / opts.len;
dieY = h / 2 / opts.len;
});
```

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