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` ````
<canvas id="rainbow"></canvas>
```

` ````
body {
background: #13142b;
}
canvas {
opacity: .6;
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
}
```

` ````
// VARS
const DPR = window.devicePixelRatio
const colors = [
['#EC008C', '#f957b6'],
['#EF4136', '#ff7972'],
['yellow', '#fff'],
['lime', '#7aff7a'],
['#27AAE1', '#5ec8f2'],
["#662D91", '#a158d8']
]
const tau = Math.PI * 2
const start = Math.PI // Start position
const finish = .5 // Finish (in % of circle "tau" basically ending at Math.PI * 2)
const inc = .007
const rainbowHeight = .5 // of view height
const arcStagger = .05 // in %
const sparklesInPerStripe = 3
let sparkles = []
// UTILS
const clamp = (min, max, val) => {
return Math.min(Math.max(min, val), max)
}
const boolRandom = () => {
return Math.round(Math.random()) ? false : true
}
// CANVAS
const sizeCanvas = () => {
radius = clamp(15, 50, window.innerWidth / 60 / DPR)
const canvas = document.getElementById('rainbow')
canvas.width = window.innerWidth * DPR
canvas.height = window.innerHeight * DPR
}
// SPARKLE PROPS
const addRandom = function (lineWidth) {
return (boolRandom() ? -1 : 1) * Math.random() * lineWidth
}
const makeSparkle = ({cx, cy, radiusX, radiusY, endAngle, lineWidth, color}) => {
return {
x: cx + radiusX * Math.cos(endAngle) + addRandom(lineWidth), // stay out in front
y: cy + radiusY * Math.sin(endAngle) + addRandom(lineWidth),
opacity: 1,
color,
rad: Math.max(radius * Math.random() * DPR, 15)
}
}
// ANIMATE
function animate(percent = 0) {
const doneAnimatingIn = percent >= finish + arcStagger * colors.length // animating in rainbow arcs
let width = window.innerWidth * DPR
let height = window.innerHeight * DPR
const lineWidth = height * .5 / colors.length
const cx = width / 2
const startCy = height + lineWidth * rainbowHeight + (height - colors.length * lineWidth) / 3 // Possibly simplify this... but the math is good :)
const startRadiusX = width / 2 + colors.length * lineWidth * 2
const startRadiusY = height
let ctx = document.getElementById('rainbow').getContext('2d')
ctx.clearRect(0, 0, width, height);
ctx.globalAlpha = 1;
ctx.lineWidth = lineWidth
for (let i = colors.length - 1; i > -1; i--) {
const [colorLine, colorSparkle] = colors[i]
const cy = startCy + i * (lineWidth / 2 - 1) // - 1 for overlap
// Making these "concentric" ellipses
const radiusX = startRadiusX - i * lineWidth / 2
const radiusY = startRadiusY - i * lineWidth / 2
const endAngle = tau * (percent - i * arcStagger) + start
const angle = clamp(start, tau * finish + start, endAngle)
// DRAW ONE OF OUR ELLIPSE LINES
// - One color of our rainbow
ctx.beginPath()
ctx.shadowColor = colorLine
ctx.strokeStyle = colorLine
ctx.ellipse(
cx,
cy,
radiusX,
radiusY,
0,
start,
angle,
false
)
ctx.lineCap = "round"
ctx.stroke()
ctx.closePath()
if (!doneAnimatingIn) {
// ADD: Animating in sparkles, follow the start of each color
for (let j = 0; j < sparklesInPerStripe; j++) {
sparkles.push(
makeSparkle({cx, cy, radiusX, radiusY, endAngle: angle, lineWidth, color: colorLine})
)
}
} else {
// ADD: Normal sparkles after animating in
sparkles.push(makeSparkle({cx, cy, radiusX, radiusY, endAngle: Math.random() * Math.PI + Math.PI, lineWidth, color: boolRandom() ? '#fff' : colorSparkle}))
}
}
// PAINT THE SPARKLES
// and get next sparkles ready too
const nextSparkles = []
for (let i = 0, len = sparkles.length; i < len; i++) {
const {x, y, opacity, color, rad} = sparkles[i]
ctx.beginPath()
ctx.globalAlpha = opacity;
ctx.fillStyle = color
ctx.arc(x - rad, y - rad, rad, 0, Math.PI / 2);
ctx.arc(x - rad, y + rad, rad, 3 * Math.PI / 2, 2 * Math.PI);
ctx.arc(x + rad, y + rad, rad, Math.PI, 3 * Math.PI / 2);
ctx.arc(x + rad, y - rad, rad, Math.PI / 2, Math.PI);
ctx.fill()
// Sparkles we are keeping
if (opacity > .2 && rad > .2) {
nextSparkles.push({
x,
y,
opacity: opacity - .03,
rad: rad - .2,
color
})
}
}
sparkles = nextSparkles
if (!doneAnimatingIn) {
// Animating in our rainbow
requestAnimationFrame(function () {
animate(percent + inc)
})
} else {
// Resume sparkles on static rainbow
requestAnimationFrame(function () {
animate(finish + colors.length * arcStagger)
})
}
}
sizeCanvas()
requestAnimationFrame(function () {animate()})
window.addEventListener('resize', sizeCanvas)
```

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