A Pen By
Art Carvajal
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` ````
<canvas id="canvas"></canvas>
<p style="position: fixed; top: 0;"></p>
<!-- try clicking! -->
```

` ````
body {
margin: 0;
overflow: hidden;
background-color: taupe;
cursor: crosshair;
}
```

` ````
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
canvas.width = innerWidth;
canvas.height = innerHeight;
window.addEventListener('resize', function(){
canvas.width = innerWidth;
canvas.height = innerHeight;
})
var numFilings = Math.round(innerWidth * 1.5);
var filingLength = 12;
var magWidth = innerWidth / 2;
var magHeight = magWidth / 7;
var mouseX = innerWidth / 2;
var mouseY = innerHeight/2;
var moving = 0;
var magnetVisible = 1;
var poleN = mouseX - magWidth/2 + magHeight/2;
var poleS = mouseX + magWidth/2 - magHeight/2;
function Filing() {
this.x = Math.random() * innerWidth;
this.y = Math.random() * innerHeight;
this.facing = Math.random() * 2;
this.nearN;
this.nearS;
this.length = Math.random();
this.dynamicSpeed = 0.04 + Math.random() * 0.04;
}
Filing.prototype.rotate = function() {
var deltaX, deltaY, theta, pX, bias;
if (this.x < mouseX) {
pX = poleN;
this.nearN = 1;
this.nearS = 0;
} else {
pX = poleS;
this.nearN = 0;
this.nearS = 1;
}
if (this.x < poleN || this.x > poleS) {
deltaX = pX - this.x;
deltaY = mouseY - this.y;
theta = Math.atan(deltaY / deltaX);
if (this.nearS) { theta += Math.PI; }
} else {
bias = Math.abs((this.x - mouseX)/(pX - mouseX));
deltaX = pX - this.x;
deltaY = (mouseY - this.y) * bias;
theta = Math.atan(deltaY / deltaX) + Math.PI;
if (this.nearS) { theta += Math.PI; }
}
this.facing = theta / Math.PI;
};
Filing.prototype.drawNormal = function() {
ctx.strokeStyle = this.nearN ? '#f00' : '#00f';
var x1 = this.x + Math.cos(Math.PI * this.facing) * filingLength;
var y1 = this.y + Math.sin(Math.PI * this.facing) * filingLength;
var x2 = this.x + Math.cos(Math.PI * (this.facing + 1)) * filingLength;
var y2 = this.y + Math.sin(Math.PI * (this.facing + 1)) * filingLength;
ctx.beginPath();
ctx.moveTo(x1,y1);
ctx.lineTo(x2,y2);
ctx.stroke();
};
Filing.prototype.drawDynamic = function() {
this.length + this.dynamicSpeed >= 1 ? (this.length = 0,
this.x = Math.random() * innerWidth,
this.y = Math.random() * innerHeight,
this.rotate()
) : this.length += this.dynamicSpeed;
var lightness = 60 * this.length;
if (this.nearN) {
ctx.strokeStyle = 'hsl(0,100%,' + lightness + '%)';
var x1 = this.x + Math.cos(Math.PI * this.facing) * (filingLength * this.length * 2);
var y1 = this.y + Math.sin(Math.PI * this.facing) * (filingLength * this.length * 2);
ctx.beginPath();
ctx.moveTo(this.x,this.y);
ctx.lineTo(x1,y1);
ctx.stroke();
} else {
ctx.strokeStyle = 'hsl(240,100%,' + lightness + '%)';
ctx.strokeStyle = this.nearN ? 'hsl(0,100%,' + lightness + '%)' : 'hsl(240,100%,' + lightness + '%)';
var x1 = this.x - Math.cos(Math.PI * this.facing) * (filingLength * this.length * 2);
var y1 = this.y - Math.sin(Math.PI * this.facing) * (filingLength * this.length * 2);
ctx.beginPath();
ctx.moveTo(this.x, this.y);
ctx.lineTo(x1, y1);
ctx.stroke();
}
};
var filings = [];
for (var i = 0; i < numFilings; i++) {
filings.push(new Filing);
filings[i].rotate();
}
document.addEventListener('mousemove', function(e){
e.preventDefault();
moving = 1;
mouseX = e.clientX;
mouseY = e.clientY;
poleN = mouseX - magWidth/2 + magHeight/2;
poleS = mouseX + magWidth/2 - magHeight/2;
})
document.addEventListener('touchmove', function(e) {
e.preventDefault();
mouseX = e.touches[0].pageX;
mouseY = e.touches[0].pageY;
moving = 1;
poleN = mouseX - magWidth/2 + magHeight/2;
poleS = mouseX + magWidth/2 - magHeight/2;
}, false);
document.addEventListener('click', function(e){
e.preventDefault();
magnetVisible = magnetVisible ? 0 : 1;
})
function drawMagnet() {
ctx.fillStyle = '#c00';
ctx.fillRect(mouseX - magWidth/2, mouseY - magHeight/2, magWidth/2, magHeight);
ctx.fillStyle = "#ddd";
ctx.fillRect(mouseX, mouseY - magHeight/2, magWidth/2, magHeight);
}
function drawAttrPoints() {
ctx.fillStyle = '#fff';
ctx.fillRect(poleN - 1, mouseY - 1, 2, 2);
ctx.fillRect(poleS - 1, mouseY - 1, 2, 2);
}
function animate() {
if (magnetVisible) { ctx.clearRect(0, 0, innerWidth, innerHeight); }
else {
ctx.fillStyle = 'rgba(0, 0, 0, 0.6)';
ctx.fillRect(0, 0, innerWidth, innerHeight);
}
for (var i = 0; i < filings.length; i++) {
if (magnetVisible) { filings[i].drawNormal(); }
else { filings[i].drawDynamic(); }
if (moving) { filings[i].rotate(); }
}
if (mouseX && magnetVisible) {
drawMagnet();
} else {
drawAttrPoints();
}
moving = 0;
window.requestAnimationFrame(animate);
}
animate();
```

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