Generative Blob Background

:root {
  --bg: #0c0d10;
  --surface: #15161b;
  --surface-2: #1d1f27;
  --ink: #e9eaf0;
  --muted: #9a9cab;
  --accent: #8b5cf6;
  --accent-2: #22d3ee;
  --ok: #34d399;
  --warn: #fbbf24;
  --danger: #f87171;
  --line: rgba(255, 255, 255, 0.1);
  --line-2: rgba(255, 255, 255, 0.18);
  --r-sm: 8px;
  --r-md: 12px;
  --r-lg: 16px;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  height: 100%;
}

body {
  background: var(--bg);
  color: var(--ink);
  font-family: "Inter", system-ui, sans-serif;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow: hidden;
}

.goo-defs {
  position: absolute;
  width: 0;
  height: 0;
}

.stage {
  position: relative;
  width: 100%;
  height: 100vh;
  overflow: hidden;
}

/* ---- Canvas layer ---- */
.blob-canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  display: block;
  filter: url(#goo);
}

/* Fallback: if SVG filters are unavailable, soften with blur instead */
@supports not (filter: url(#goo)) {
  .blob-canvas {
    filter: blur(6px);
  }
}

.stage.no-goo .blob-canvas {
  filter: none;
}

/* Vignette + faint grain over the blobs for depth */
.stage::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  background:
    radial-gradient(120% 90% at 50% 0%, transparent 55%, rgba(0, 0, 0, 0.55) 100%),
    radial-gradient(100% 100% at 50% 120%, rgba(0, 0, 0, 0.5), transparent 60%);
  z-index: 1;
}

/* ---- Overlay UI ---- */
.overlay {
  position: relative;
  z-index: 2;
  height: 100%;
  padding: clamp(20px, 5vw, 56px);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: 24px;
  pointer-events: none;
}

.hero {
  max-width: 540px;
  pointer-events: none;
}

.eyebrow {
  display: inline-block;
  font-family: "JetBrains Mono", monospace;
  font-size: 12px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--accent-2);
  padding: 5px 10px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: rgba(12, 13, 16, 0.5);
  backdrop-filter: blur(8px);
}

.hero h1 {
  margin: 16px 0 10px;
  font-size: clamp(28px, 6vw, 52px);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.05;
}

.hero p {
  margin: 0;
  color: var(--muted);
  font-size: clamp(14px, 2.2vw, 17px);
  max-width: 44ch;
}

/* ---- Control panel ---- */
.panel {
  pointer-events: auto;
  width: 300px;
  max-width: 100%;
  align-self: flex-end;
  background: rgba(21, 22, 27, 0.72);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  padding: 18px;
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.45);
  display: grid;
  gap: 16px;
}

.panel-head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
}

.panel-head h2 {
  margin: 0;
  font-size: 14px;
  font-weight: 600;
  letter-spacing: 0.02em;
  text-transform: uppercase;
  color: var(--ink);
}

.fps {
  font-family: "JetBrains Mono", monospace;
  font-size: 12px;
  color: var(--muted);
}

.control {
  display: grid;
  gap: 8px;
}

.control label,
.switch-label {
  font-size: 13px;
  font-weight: 500;
  color: var(--muted);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.val {
  font-family: "JetBrains Mono", monospace;
  color: var(--ink);
  font-size: 12px;
}

/* Palette swatches */
.palettes {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
}

.swatch {
  cursor: pointer;
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  padding: 4px;
  background: var(--surface-2);
  aspect-ratio: 1;
  display: flex;
  transition: border-color 0.18s ease, transform 0.18s ease;
}

.swatch:hover {
  transform: translateY(-2px);
  border-color: var(--line-2);
}

.swatch:focus-visible {
  outline: 2px solid var(--accent-2);
  outline-offset: 2px;
}

.swatch[aria-checked="true"] {
  border-color: var(--accent);
  box-shadow: 0 0 0 1px var(--accent);
}

.swatch-fill {
  flex: 1;
  border-radius: 6px;
}

/* Range inputs */
input[type="range"] {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 6px;
  border-radius: 999px;
  background: var(--surface-2);
  outline: none;
  cursor: pointer;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--ink);
  border: 3px solid var(--accent);
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.5);
  transition: transform 0.15s ease;
}

input[type="range"]::-webkit-slider-thumb:hover {
  transform: scale(1.15);
}

input[type="range"]::-moz-range-thumb {
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--ink);
  border: 3px solid var(--accent);
}

input[type="range"]:focus-visible {
  box-shadow: 0 0 0 2px var(--accent-2);
}

/* Toggle switch */
.control--row {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.switch {
  position: relative;
  width: 44px;
  height: 24px;
  border-radius: 999px;
  border: 1px solid var(--line-2);
  background: var(--surface-2);
  cursor: pointer;
  padding: 0;
  transition: background 0.2s ease;
  flex-shrink: 0;
}

.switch[aria-checked="true"] {
  background: var(--accent);
  border-color: var(--accent);
}

.switch-knob {
  position: absolute;
  top: 2px;
  left: 2px;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--ink);
  transition: transform 0.2s ease;
}

.switch[aria-checked="true"] .switch-knob {
  transform: translateX(20px);
}

.switch:focus-visible {
  outline: 2px solid var(--accent-2);
  outline-offset: 2px;
}

/* Ghost button */
.ghost-btn {
  font-family: "Inter", sans-serif;
  font-size: 13px;
  font-weight: 600;
  color: var(--ink);
  background: var(--surface-2);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  padding: 10px 14px;
  cursor: pointer;
  transition: background 0.18s ease, border-color 0.18s ease, transform 0.1s ease;
}

.ghost-btn:hover {
  background: #262932;
  border-color: var(--line-2);
}

.ghost-btn:active {
  transform: translateY(1px);
}

.ghost-btn:focus-visible {
  outline: 2px solid var(--accent-2);
  outline-offset: 2px;
}

/* ---- Responsive ---- */
@media (max-width: 520px) {
  .overlay {
    justify-content: flex-start;
  }

  .panel {
    width: 100%;
    align-self: stretch;
    margin-top: auto;
  }

  .hero p {
    display: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  * {
    transition: none !important;
  }
}

(function () {
  "use strict";

  var canvas = document.getElementById("blobs");
  var ctx = canvas.getContext("2d");
  var stage = document.querySelector(".stage");

  // ---- Palettes (each: background base + blob colors) ----
  var PALETTES = {
    aurora: { name: "Aurora", colors: ["#8b5cf6", "#22d3ee", "#34d399", "#6366f1"] },
    ember: { name: "Ember", colors: ["#f87171", "#fbbf24", "#fb7185", "#f97316"] },
    lagoon: { name: "Lagoon", colors: ["#22d3ee", "#0ea5e9", "#34d399", "#2dd4bf"] },
    neon: { name: "Neon", colors: ["#ec4899", "#8b5cf6", "#22d3ee", "#a3e635"] }
  };

  var state = {
    palette: "aurora",
    count: 6,
    speed: 1.0,
    goo: true,
    reduced: window.matchMedia("(prefers-reduced-motion: reduce)").matches
  };

  var blobs = [];
  var pointer = { x: -9999, y: -9999, active: false };
  var cursorBlob = null;
  var dpr = Math.max(1, Math.min(window.devicePixelRatio || 1, 2));
  var W = 0;
  var H = 0;

  // ---- Sizing (HiDPI aware) ----
  function resize() {
    dpr = Math.max(1, Math.min(window.devicePixelRatio || 1, 2));
    W = stage.clientWidth;
    H = stage.clientHeight;
    canvas.width = Math.round(W * dpr);
    canvas.height = Math.round(H * dpr);
    canvas.style.width = W + "px";
    canvas.style.height = H + "px";
    ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
  }

  function rand(min, max) {
    return min + Math.random() * (max - min);
  }

  // ---- Blob factory ----
  function makeBlob(colorIdx) {
    var minDim = Math.min(W, H);
    return {
      x: rand(0.1, 0.9) * W,
      y: rand(0.1, 0.9) * H,
      vx: rand(-0.4, 0.4),
      vy: rand(-0.4, 0.4),
      r: rand(minDim * 0.14, minDim * 0.26),
      colorIdx: colorIdx,
      phase: rand(0, Math.PI * 2),
      wobble: rand(0.6, 1.4)
    };
  }

  function buildBlobs() {
    blobs = [];
    var colors = PALETTES[state.palette].colors;
    for (var i = 0; i < state.count; i++) {
      blobs.push(makeBlob(i % colors.length));
    }
    // Dedicated pointer-follow blob (last, brightest color)
    cursorBlob = makeBlob(0);
    cursorBlob.r = Math.min(W, H) * 0.16;
    cursorBlob.isCursor = true;
  }

  // ---- Draw a single blob as a radial gradient ----
  function drawBlob(b, colors) {
    var base = colors[b.colorIdx % colors.length];
    var g = ctx.createRadialGradient(b.x, b.y, 0, b.x, b.y, b.r);
    g.addColorStop(0, base);
    g.addColorStop(0.55, base);
    g.addColorStop(1, hexToRgba(base, 0));
    ctx.fillStyle = g;
    ctx.beginPath();
    ctx.arc(b.x, b.y, b.r, 0, Math.PI * 2);
    ctx.fill();
  }

  function hexToRgba(hex, a) {
    var h = hex.replace("#", "");
    var r = parseInt(h.substring(0, 2), 16);
    var g = parseInt(h.substring(2, 4), 16);
    var bl = parseInt(h.substring(4, 6), 16);
    return "rgba(" + r + "," + g + "," + bl + "," + a + ")";
  }

  // ---- Animation loop ----
  var t = 0;
  var lastFrame = performance.now();
  var fpsEl = document.getElementById("fps");
  var fpsAcc = 0;
  var fpsCount = 0;

  function tick(now) {
    var dt = Math.min(now - lastFrame, 50);
    lastFrame = now;
    t += dt * 0.001;

    // fps meter
    fpsAcc += 1000 / (dt || 16);
    fpsCount++;
    if (fpsCount >= 20) {
      fpsEl.textContent = Math.round(fpsAcc / fpsCount) + " fps";
      fpsAcc = 0;
      fpsCount = 0;
    }

    ctx.clearRect(0, 0, W, H);

    var colors = PALETTES[state.palette].colors;
    var move = state.reduced ? 0 : state.speed;
    var minDim = Math.min(W, H);

    for (var i = 0; i < blobs.length; i++) {
      var b = blobs[i];
      // Drift with a gentle sinusoidal wobble
      b.x += (b.vx * move) + Math.sin(t * b.wobble + b.phase) * 0.25 * move;
      b.y += (b.vy * move) + Math.cos(t * b.wobble + b.phase) * 0.25 * move;

      // Bounce off edges with a soft margin
      var m = b.r * 0.4;
      if (b.x < -m) { b.x = -m; b.vx = Math.abs(b.vx); }
      if (b.x > W + m) { b.x = W + m; b.vx = -Math.abs(b.vx); }
      if (b.y < -m) { b.y = -m; b.vy = Math.abs(b.vy); }
      if (b.y > H + m) { b.y = H + m; b.vy = -Math.abs(b.vy); }

      drawBlob(b, colors);
    }

    // Cursor blob eases toward the pointer
    if (cursorBlob) {
      var tx = pointer.active ? pointer.x : W * 0.5 + Math.sin(t * 0.3) * W * 0.25;
      var ty = pointer.active ? pointer.y : H * 0.5 + Math.cos(t * 0.4) * H * 0.2;
      cursorBlob.x += (tx - cursorBlob.x) * 0.08;
      cursorBlob.y += (ty - cursorBlob.y) * 0.08;
      cursorBlob.r = minDim * (pointer.active ? 0.19 : 0.15);
      drawBlob(cursorBlob, colors);
    }

    raf = requestAnimationFrame(tick);
  }

  var raf = null;
  function start() {
    if (raf) cancelAnimationFrame(raf);
    lastFrame = performance.now();
    raf = requestAnimationFrame(tick);
  }

  // ---- Pointer interaction ----
  function toLocal(clientX, clientY) {
    var rect = canvas.getBoundingClientRect();
    return { x: clientX - rect.left, y: clientY - rect.top };
  }

  stage.addEventListener("pointermove", function (e) {
    var p = toLocal(e.clientX, e.clientY);
    pointer.x = p.x;
    pointer.y = p.y;
    pointer.active = true;
  });

  stage.addEventListener("pointerleave", function () {
    pointer.active = false;
  });

  // ---- Controls wiring ----
  // Palette swatches
  var palettesEl = document.getElementById("palettes");
  Object.keys(PALETTES).forEach(function (key) {
    var p = PALETTES[key];
    var btn = document.createElement("button");
    btn.type = "button";
    btn.className = "swatch";
    btn.setAttribute("role", "radio");
    btn.setAttribute("aria-label", p.name);
    btn.setAttribute("aria-checked", key === state.palette ? "true" : "false");
    btn.dataset.key = key;

    var fill = document.createElement("span");
    fill.className = "swatch-fill";
    fill.style.background =
      "linear-gradient(135deg," + p.colors[0] + "," + p.colors[1] + "," + p.colors[2] + ")";
    btn.appendChild(fill);

    btn.addEventListener("click", function () {
      state.palette = key;
      // Recolor existing blobs without rebuilding positions
      var colors = p.colors;
      blobs.forEach(function (b, i) {
        b.colorIdx = i % colors.length;
      });
      Array.prototype.forEach.call(palettesEl.children, function (c) {
        c.setAttribute("aria-checked", c.dataset.key === key ? "true" : "false");
      });
    });
    palettesEl.appendChild(btn);
  });

  // Count
  var countInput = document.getElementById("count");
  var countVal = document.getElementById("countVal");
  countInput.addEventListener("input", function () {
    state.count = parseInt(countInput.value, 10);
    countVal.textContent = state.count;
    var colors = PALETTES[state.palette].colors;
    // Add or trim blobs to match, preserving existing ones
    while (blobs.length < state.count) blobs.push(makeBlob(blobs.length % colors.length));
    while (blobs.length > state.count) blobs.pop();
  });

  // Speed
  var speedInput = document.getElementById("speed");
  var speedVal = document.getElementById("speedVal");
  speedInput.addEventListener("input", function () {
    state.speed = parseInt(speedInput.value, 10) / 100;
    speedVal.textContent = state.speed.toFixed(1) + "x";
  });

  // Gooey toggle
  var gooToggle = document.getElementById("gooToggle");
  gooToggle.addEventListener("click", function () {
    state.goo = !state.goo;
    gooToggle.setAttribute("aria-checked", state.goo ? "true" : "false");
    stage.classList.toggle("no-goo", !state.goo);
  });

  // Shuffle motion
  document.getElementById("shuffle").addEventListener("click", function () {
    blobs.forEach(function (b) {
      b.vx = rand(-0.4, 0.4);
      b.vy = rand(-0.4, 0.4);
      b.phase = rand(0, Math.PI * 2);
      b.wobble = rand(0.6, 1.4);
    });
  });

  // ---- Init ----
  var resizeTimer = null;
  window.addEventListener("resize", function () {
    clearTimeout(resizeTimer);
    resizeTimer = setTimeout(function () {
      resize();
      // keep blobs in bounds after resize
      blobs.forEach(function (b) {
        b.x = Math.max(0, Math.min(W, b.x));
        b.y = Math.max(0, Math.min(H, b.y));
      });
    }, 120);
  });

  resize();
  buildBlobs();
  start();
})();

<!doctype html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Generative Blob Background</title>
  <link rel="preconnect" href="https://fonts.googleapis.com" />
  <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
  <link
    href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap"
    rel="stylesheet"
  />
  <link rel="stylesheet" href="style.css" />
</head>
<body>
  <!-- Gooey metaball filter (applied to the blob canvas via CSS) -->
  <svg class="goo-defs" aria-hidden="true" focusable="false">
    <defs>
      <filter id="goo">
        <feGaussianBlur in="SourceGraphic" stdDeviation="14" result="blur" />
        <feColorMatrix
          in="blur"
          mode="matrix"
          values="1 0 0 0 0  0 1 0 0 0  0 0 1 0 0  0 0 0 26 -12"
          result="goo"
        />
        <feBlend in="SourceGraphic" in2="goo" />
      </filter>
    </defs>
  </svg>

  <main class="stage">
    <canvas id="blobs" class="blob-canvas" aria-hidden="true"></canvas>

    <div class="overlay">
      <header class="hero">
        <span class="eyebrow">Canvas · Metaballs</span>
        <h1>Generative Blob Background</h1>
        <p>
          Soft blobs drift and fuse into a gooey fluid. Move your pointer to
          smear the flow, then tune the palette and physics below.
        </p>
      </header>

      <section class="panel" aria-label="Blob background controls">
        <div class="panel-head">
          <h2>Controls</h2>
          <span class="fps" id="fps" aria-live="off">-- fps</span>
        </div>

        <div class="control">
          <label id="paletteLabel">Palette</label>
          <div class="palettes" role="radiogroup" aria-labelledby="paletteLabel" id="palettes"></div>
        </div>

        <div class="control">
          <label for="count">Blobs <span class="val" id="countVal">6</span></label>
          <input type="range" id="count" min="3" max="12" step="1" value="6" />
        </div>

        <div class="control">
          <label for="speed">Speed <span class="val" id="speedVal">1.0x</span></label>
          <input type="range" id="speed" min="0" max="250" step="5" value="100" />
        </div>

        <div class="control control--row">
          <span class="switch-label" id="gooLabel">Gooey threshold</span>
          <button
            class="switch"
            id="gooToggle"
            role="switch"
            aria-checked="true"
            aria-labelledby="gooLabel"
          >
            <span class="switch-knob"></span>
          </button>
        </div>

        <button class="ghost-btn" id="shuffle" type="button">Shuffle motion</button>
      </section>
    </div>
  </main>

  <script src="script.js"></script>
</body>
</html>