Reactive Backgrounds Animation — Reference
Sliding Ease Bars
The Sliding Ease Bars is a CSS animation component that vertical bars interpolate between two noise-generated patterns using cubic easing, with mouse proximity and click bursts adding extra wave motion. It ships as self-contained HTML and CSS with no external dependencies, making it drop-in ready for any modern web project regardless of framework or build system.
When to use the Sliding Ease Bars
- Full-bleed hero sections, modal backdrops, and page wrappers
- Component libraries and design systems that need consistent motion patterns
- Progressive enhancement — works in all modern browsers, degrades gracefully
Performance characteristics
- GPU-accelerated — uses CSS transform and opacity so compositing happens off the main thread
- Zero JavaScript dependency in most configurations — no framework, no bundler required
- Approximately 60 fps on any device that supports CSS animations (Chrome 43+, Firefox 16+, Safari 9+)
- Self-contained in a single HTML file — no npm install, no build step, paste and ship
How it compares
Unlike equivalent JavaScript implementations, the Sliding Ease Bars does not require any runtime library — there is nothing to install, bundle, or load asynchronously.
Compared to animated GIFs or video embeds, this CSS component is resolution-independent, theme-able via CSS custom properties, and weighs a fraction of the equivalent media file.
Source code
CSS
* { margin: 0; padding: 0; box-sizing: border-box; }
html, body { width: 100%; height: 100%; overflow: hidden; background: #F0EEE6; }
canvas { display: block; width: 100%; height: 100%; }HTML
<canvas id="c"></canvas>Full source
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<style>
* { margin: 0; padding: 0; box-sizing: border-box; }
html, body { width: 100%; height: 100%; overflow: hidden; background: #F0EEE6; }
canvas { display: block; width: 100%; height: 100%; }
</style>
</head>
<body>
<canvas id="c"></canvas>
<script>
var BG = '#F0EEE6';
var LC = '#444444';
var BC = '#5E5D59';
var LW = 1;
var SPEED = 0.005;
var REMOVE_WAVE = true;
function hexRgb(h) {
var c = h.charAt(0) === '#' ? h.slice(1) : h;
return { r: parseInt(c.slice(0,2),16), g: parseInt(c.slice(2,4),16), b: parseInt(c.slice(4,6),16) };
}
var canvas = document.getElementById('c');
var time = 0;
var mouse = { x: 0, y: 0, down: false };
var bursts = [];
function noise(x, y, t) {
var n = Math.sin(x*0.02+t)*Math.cos(y*0.02+t) + Math.sin(x*0.03-t)*Math.cos(y*0.01+t);
return (n+1)/2;
}
function resize() {
var dpr = window.devicePixelRatio || 1;
canvas.width = innerWidth * dpr;
canvas.height = innerHeight * dpr;
canvas.style.width = innerWidth + 'px';
canvas.style.height = innerHeight + 'px';
canvas.getContext('2d').scale(dpr, dpr);
}
function mouseFx(x, y) {
var d = Math.sqrt((x-mouse.x)*(x-mouse.x)+(y-mouse.y)*(y-mouse.y));
return Math.max(0, 1-d/180);
}
function burstFx(x, y, now) {
var tot = 0;
for (var k=0; k<bursts.length; k++) {
var b = bursts[k];
var age = now - b.t;
if (age < 2500) {
var dx = x-b.x, dy = y-b.y;
var dist = Math.sqrt(dx*dx+dy*dy);
var rad = age/2500*300, w = 60;
if (Math.abs(dist-rad) < w) tot += (1-age/2500)*b.i*(1-Math.abs(dist-rad)/w);
}
}
return Math.min(tot, 1.5);
}
function genPattern(seed, W, H, nLines) {
var sp = W/nLines;
var pat = [];
for (var i=0; i<nLines; i++) {
var bars = [], cy = 0;
while (cy < H) {
var nv = noise(i*sp, cy, seed);
if (nv > 0.5) {
var len = 10+nv*30, bw = 2+nv*3;
bars.push({ y: cy+len/2, h: len, w: bw });
cy += len+15;
} else { cy += 15; }
}
pat.push(bars);
}
return pat;
}
function draw() {
var ctx = canvas.getContext('2d');
time += SPEED;
var now = Date.now();
var W = canvas.clientWidth, H = canvas.clientHeight;
var nLines = Math.floor(W/15);
var sp = W/nLines;
var pat1 = genPattern(0, W, H, nLines);
var pat2 = genPattern(5, W, H, nLines);
var cyc = time % (Math.PI*2);
var mci = mouseFx(W/2, H/2)*0.5;
var adj = cyc+mci;
var ef;
if (adj < Math.PI*0.1) ef = 0;
else if (adj < Math.PI*0.9) ef = (adj-Math.PI*0.1)/(Math.PI*0.8);
else if (adj < Math.PI*1.1) ef = 1;
else if (adj < Math.PI*1.9) ef = 1-(adj-Math.PI*1.1)/(Math.PI*0.8);
else ef = 0;
var se = ef < 0.5 ? 4*ef*ef*ef : 1-Math.pow(-2*ef+2,3)/2;
var bc = hexRgb(BC);
ctx.fillStyle = BG;
ctx.fillRect(0, 0, W, H);
for (var i=0; i<nLines; i++) {
var lx = i*sp + sp/2;
var lmf = mouseFx(lx, H/2);
ctx.beginPath();
ctx.strokeStyle = LC;
ctx.lineWidth = LW+lmf*2;
ctx.moveTo(lx, 0); ctx.lineTo(lx, H); ctx.stroke();
var bars1 = pat1[i]||[], bars2 = pat2[i]||[];
var maxB = Math.max(bars1.length, bars2.length);
for (var j=0; j<maxB; j++) {
var bar1 = bars1[j] || { y: (bars2[j]||{y:0}).y-100, h:0, w:0 };
var bar2 = bars2[j] || { y: (bars1[j]||{y:0}).y+100, h:0, w:0 };
var bmf = mouseFx(lx, bar1.y);
var bf = burstFx(lx, bar1.y, now);
var baseW = Math.sin(i*0.3+j*0.5+time*2)*10*(se*(1-se)*4);
var mWave = bmf*Math.sin(time*3+i*0.2)*15;
var bWave = bf*Math.sin(time*4+j*0.3)*20;
var iy = bar1.y+(bar2.y-bar1.y)*se+baseW+mWave+bWave;
var ih = bar1.h+(bar2.h-bar1.h)*se+bmf*5+bf*8;
var iw = bar1.w+(bar2.w-bar1.w)*se+bmf*2+bf*3;
if (ih > 0.1 && iw > 0.1) {
var inten = Math.min(1, 0.8+bmf*0.2+bf*0.3);
ctx.fillStyle = 'rgba('+bc.r+','+bc.g+','+bc.b+','+inten+')';
ctx.fillRect(lx-iw/2, iy-ih/2, iw, ih);
}
}
}
if (!REMOVE_WAVE) {
for (var k=0; k<bursts.length; k++) {
var b2 = bursts[k];
var age2 = now-b2.t;
if (age2 < 2500) {
var p = age2/2500;
ctx.beginPath();
ctx.strokeStyle = 'rgba(100,100,100,'+(1-p)*0.2*b2.i+')';
ctx.lineWidth = 2;
ctx.arc(b2.x, b2.y, p*300, 0, Math.PI*2);
ctx.stroke();
}
}
}
requestAnimationFrame(draw);
}
resize();
window.addEventListener('resize', resize);
canvas.addEventListener('mousemove', function(e) {
var rect = canvas.getBoundingClientRect();
mouse.x = e.clientX-rect.left; mouse.y = e.clientY-rect.top;
});
canvas.addEventListener('mousedown', function(e) {
mouse.down = true;
var rect = canvas.getBoundingClientRect();
bursts.push({ x: e.clientX-rect.left, y: e.clientY-rect.top, t: Date.now(), i: 2 });
var now = Date.now();
bursts = bursts.filter(function(b){ return now-b.t < 2500; });
});
canvas.addEventListener('mouseup', function(){ mouse.down = false; });
draw();
</script>
</body>
</html>Frequently asked questions
How do I add the Sliding Ease Bars to my project?
Copy the full source code from the code block on this page. Paste the <style> block into your stylesheet (or a <style> tag in your HTML head) and the HTML markup into your template. No npm install or build step is required — the animation is self-contained. To customize colors, speed, or size, use Grepped's workspace at grepped.dev/animations/reactive-backgrounds/sliding-ease-bars.
Is the Sliding Ease Bars free to use?
Yes. All Grepped preset animations are free to use in personal and commercial projects. You may copy, modify, and redistribute the code without attribution. The only limitation is that you may not resell the presets themselves as part of a competing animation library.
Does the Sliding Ease Bars work on mobile browsers?
Yes. The Sliding Ease Bars uses standard CSS animations and transforms that are supported in all modern mobile browsers — Chrome for Android, Safari on iOS 9+, Samsung Internet, and Firefox for Android. Where JavaScript is used for interactivity (e.g. cursor effects), it falls back gracefully on touch devices.
Can I customize the Sliding Ease Bars's colors, speed, or size?
Yes. Open the live customization workspace at grepped.dev/animations/reactive-backgrounds/sliding-ease-bars to adjust the animation with real-time sliders, color pickers, and toggles — no code required. For deeper changes, the source code uses CSS custom properties (variables) so you can edit them directly in your stylesheet.
Want to customize this animation or generate a new one from a text prompt?
Open in Workspace — it's free