A Pen By
Riley Shaw

` ````
body
background: #222
canvas
position: absolute
top: 50%
left: 50%
transform: translate3d(-50%, -50%, 0)
border-radius: 30px
box-shadow: 0 0 24px 8px rgba(0, 0, 0, 0.2)
cursor: pointer
```

` ````
const PX = 600;
const FLOORS = 8;
const ITERATIONS = 1;
const FG = [102, 199, 244];
const BG = [34, 34, 34];
const HOURS = 6;
const HOUR_OFFSET = 0.5;
const SPACING = 110;
const LINE_WIDTH = 40;
const DEBUG_SMALL = false;
const DEBUG_HOURS = [];
const DEBUG_NO_CURVES = false;
const {abs, cos, floor, PI, round, random, sign, sin, sqrt} = Math;
const R = SPACING * sqrt(3)/4;
const canvas = document.createElement('canvas');
canvas.height = canvas.width = PX;
canvas.style.height = canvas.style.width = `${PX / 2}px`;
canvas.style.background = `rgb(${BG})`;
document.body.appendChild(canvas);
const ctx = canvas.getContext('2d');
// Flip the y-axis.
ctx.transform(1, 0, 0, -1, 0, PX);
ctx.lineWidth = LINE_WIDTH;
ctx.fillStyle = `rgba(${BG}, ${1.4 / FLOORS})`;
function go () {
ctx.clearRect(0, 0, PX, PX);
if (DEBUG_SMALL === true) {
ctx.strokeStyle = '#fff';
ctx.rect(PX / 4, PX / 4, PX / 2, PX / 2);
ctx.stroke();
}
for (let floor = 0; floor < FLOORS; ++floor) {
ctx.fillRect(0, 0, PX, PX);
console.log('fillin');
for (let n = 0; n < ITERATIONS; ++n) {
// Don't introduce PI etc to θ yet to avoid some precision hassles.
let hour = rand(HOURS);
let θ = (hour + HOUR_OFFSET) / HOURS * 2*PI;
let opacity = 1;
if (DEBUG_HOURS.length && DEBUG_HOURS.indexOf(hour) === -1) continue;
const p = getPosition(hour, θ);
do {
ctx.strokeStyle = `rgb(${FG})`;
ctx.beginPath();
if (DEBUG_NO_CURVES || rand(10)) {
// Draw a line straight ahead.
DEBUG_SMALL
? ctx.moveTo(p.x / 2 + PX / 4, p.y / 2 + PX / 4)
: ctx.moveTo(p.x, p.y)
;
p.x += SPACING * cos(θ);
p.y += SPACING * sin(θ);
DEBUG_SMALL
? ctx.lineTo(p.x / 2 + PX / 4, p.y / 2 + PX / 4)
: ctx.lineTo(p.x, p.y)
;
ctx.stroke();
} else {
// Once in a while, turn.
const Δ_hour = 2*rand(2) - 1; // +/- 1
const θ_1 = θ - PI/2 * Δ_hour;
// Add or subtract an hour and update the angle.
hour = (hour + Δ_hour) % HOURS;
θ = (hour + HOUR_OFFSET) / HOURS * 2*PI;
const θ_2 = θ - PI/2 * Δ_hour;
p.x += R * cos(θ_1 + PI);
p.y += R * sin(θ_1 + PI);
ctx.arc(
p.x,
p.y,
R,
θ_1,
θ_2,
Δ_hour < 0
);
p.x += R * cos(θ_2);
p.y += R * sin(θ_2);
}
ctx.stroke();
} while (
p.x > -SPACING && p.x < PX + SPACING &&
p.y > -SPACING && p.y < PX + SPACING &&
opacity > 0
);
}
}
}
// Set the position so that the lines come out of the appropriate
// wall (based on direction), in a random cell.
function getPosition (hour, θ) {
const cos_θ = +cos(θ).toFixed(6);
const sin_θ = +sin(θ).toFixed(6);
const abs_cos_θ = +abs(cos_θ);
const abs_sin_θ = +abs(sin_θ);
// One of our axes will be latched to either the min or max value.
const latched_axis = abs_cos_θ / (abs_sin_θ + abs_cos_θ) > random()
? 'x'
: 'y'
;
// The other gets a random value within the grid.
const free_axis = latched_axis === 'x'
? 'y'
: 'x'
;
// TODO(riley): Generalize.
const offset = {
x: SPACING / 3,
y: SPACING / 2,
};
const axis_spacing = {
x: (abs_cos_θ || sqrt(3)/4) * SPACING,
y: (abs_sin_θ || sqrt(3)/4) * SPACING,
};
// The direction (+1 or -1) of our line coming out of each axis.
const d = {
x: sign(cos_θ),
y: sign(sin_θ),
};
// TODO(riley): Factor LINE_WIDTH into this instead of just
// forcing it higher.
const latched_spacing = axis_spacing[latched_axis];
const p_latched = d[latched_axis] === 1
? -2*latched_spacing
: PX - PX % latched_spacing + latched_spacing
;
const free_spacing = axis_spacing[free_axis];
const p_free = free_spacing *
(rand(Math.ceil(PX / free_spacing + 2)) - 1);
return {
[latched_axis]: p_latched + offset[latched_axis],
[free_axis]: p_free + offset[free_axis],
};
}
function rand (a, b, c) {
const fn = (b === 'true' || c) ? i => i : floor;
if (typeof b !== 'number') { b = a; a = 0; }
return fn(random() * (b - a) + a);
}
function approx (n) {
return +(Math.round(n + 'e4') + 'e-4');
}
canvas.addEventListener('click', go, false);
go();
```

999px

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