Liquid Metal

/**
 * Liquid Metal — Flowing chrome gradient with animated specular highlight streak.
 * Category: backgrounds | Animate: true | Interactive: false | Complexity: medium
 */
export default function liquidMetal(ctx, state) {
  return {
    frame({ width, height, time, reducedMotion }) {
      const t = reducedMotion ? 0 : time;

      // Base chrome gradient — radial center drifts
      const cx = width * 0.5 + Math.sin(t * 0.38) * width * 0.22;
      const cy = height * 0.42 + Math.cos(t * 0.28) * height * 0.14;
      const r = Math.max(width, height) * 0.95;

      const base = ctx.createRadialGradient(cx, cy, 0, cx, cy, r);
      base.addColorStop(0, 'rgba(228, 232, 242, 1)');
      base.addColorStop(0.18, 'rgba(188, 196, 212, 1)');
      base.addColorStop(0.45, 'rgba(128, 138, 158, 1)');
      base.addColorStop(0.75, 'rgba(74,  84, 102, 1)');
      base.addColorStop(1, 'rgba(36,  42,  56, 1)');

      ctx.fillStyle = base;
      ctx.fillRect(0, 0, width, height);

      if (reducedMotion) return;

      // Specular streak — angled band of light
      const sx = width * 0.15 + Math.sin(t * 0.52 + 0.8) * width * 0.65;
      const angle = -0.38 + Math.sin(t * 0.22) * 0.12;
      const bandW = 60 + Math.sin(t * 0.35) * 20;

      ctx.save();
      ctx.translate(sx, 0);
      ctx.rotate(angle);

      const streak = ctx.createLinearGradient(-bandW, 0, bandW, 0);
      streak.addColorStop(0, 'rgba(255,255,255,0)');
      streak.addColorStop(0.35, 'rgba(255,255,255,0.28)');
      streak.addColorStop(0.5, 'rgba(255,255,255,0.55)');
      streak.addColorStop(0.65, 'rgba(255,255,255,0.28)');
      streak.addColorStop(1, 'rgba(255,255,255,0)');

      ctx.fillStyle = streak;
      ctx.fillRect(-bandW, -height, bandW * 2, height * 3);
      ctx.restore();

      // Secondary soft reflection
      const rx = width * 0.72 + Math.cos(t * 0.41 + 2) * width * 0.18;
      const ry = height * 0.3 + Math.sin(t * 0.33 + 1) * height * 0.12;
      const rg = ctx.createRadialGradient(rx, ry, 0, rx, ry, 120);
      rg.addColorStop(0, 'rgba(255,255,255,0.18)');
      rg.addColorStop(0.5, 'rgba(255,255,255,0.06)');
      rg.addColorStop(1, 'rgba(255,255,255,0)');
      ctx.fillStyle = rg;
      ctx.fillRect(0, 0, width, height);
    },
  };
}

<canvas id="canvas-effect" style="width:100%;height:400px;display:block" aria-hidden="true"></canvas>
<script>
/**
 * mountCanvas — Minimal runtime for Canvas effects.
 *
 * Handles HiDPI scaling, ResizeObserver, RAF loop, pointer tracking,
 * reduced-motion, and cleanup. The effect only implements draw logic.
 *
 * @param {HTMLCanvasElement} canvas
 * @param {(ctx: CanvasRenderingContext2D, state: object) => object} createEffect
 * @param {object} [options]
 * @returns {() => void} destroy function
 */
function mountCanvas(canvas, createEffect, options = {}) {
  const ctx = canvas.getContext('2d', { alpha: true });
  if (!ctx) throw new Error('2D context not available');

  const opts = {
    animate: true,
    clear: true,
    maxDpr: 2,
    pauseWhenHidden: true,
    respectReducedMotion: true,
    ...options,
  };

  const reducedMotion =
    opts.respectReducedMotion && window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  const state = {
    canvas,
    ctx,
    width: 0,
    height: 0,
    pixelWidth: 0,
    pixelHeight: 0,
    dpr: 1,
    time: 0,
    delta: 0,
    frame: 0,
    playing: false,
    reducedMotion,
    pointer: { x: 0, y: 0, inside: false, down: false },
  };

  let rafId = 0;
  let lastTime = 0;
  let disposed = false;

  function measure() {
    const rect = canvas.getBoundingClientRect();
    const w = Math.max(1, rect.width);
    const h = Math.max(1, rect.height);
    const dpr = Math.min(window.devicePixelRatio || 1, opts.maxDpr);
    const pw = Math.round(w * dpr);
    const ph = Math.round(h * dpr);

    if (canvas.width !== pw || canvas.height !== ph) {
      canvas.width = pw;
      canvas.height = ph;
    }

    state.width = w;
    state.height = h;
    state.pixelWidth = pw;
    state.pixelHeight = ph;
    state.dpr = dpr;
    ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
  }

  function clear() {
    ctx.clearRect(0, 0, state.width, state.height);
  }

  const effect = createEffect(ctx, state) || {};

  function onResize() {
    measure();
    effect.resize?.(state);
    if (!opts.animate || reducedMotion) {
      if (opts.clear) clear();
      effect.frame?.(state);
    }
  }

  function loop(now) {
    if (disposed) return;
    if (opts.pauseWhenHidden && document.hidden) {
      rafId = requestAnimationFrame(loop);
      return;
    }

    state.delta = lastTime ? (now - lastTime) / 1000 : 0;
    state.time = now / 1000;
    state.frame += 1;
    lastTime = now;

    if (opts.clear) clear();
    effect.frame?.(state);

    rafId = requestAnimationFrame(loop);
  }

  function onPointerMove(e) {
    const rect = canvas.getBoundingClientRect();
    state.pointer.x = e.clientX - rect.left;
    state.pointer.y = e.clientY - rect.top;
    if (!opts.animate || reducedMotion) {
      if (opts.clear) clear();
      effect.frame?.(state);
    }
  }
  function onPointerEnter() {
    state.pointer.inside = true;
  }
  function onPointerLeave() {
    state.pointer.inside = false;
    state.pointer.down = false;
  }
  function onPointerDown() {
    state.pointer.down = true;
  }
  function onPointerUp() {
    state.pointer.down = false;
  }

  const ro = new ResizeObserver(onResize);
  ro.observe(canvas);

  canvas.addEventListener('pointermove', onPointerMove);
  canvas.addEventListener('pointerenter', onPointerEnter);
  canvas.addEventListener('pointerleave', onPointerLeave);
  canvas.addEventListener('pointerdown', onPointerDown);
  window.addEventListener('pointerup', onPointerUp);

  measure();

  if (opts.animate && !reducedMotion) {
    state.playing = true;
    rafId = requestAnimationFrame(loop);
  } else {
    effect.frame?.(state);
  }

  return function destroy() {
    disposed = true;
    state.playing = false;
    cancelAnimationFrame(rafId);
    ro.disconnect();
    canvas.removeEventListener('pointermove', onPointerMove);
    canvas.removeEventListener('pointerenter', onPointerEnter);
    canvas.removeEventListener('pointerleave', onPointerLeave);
    canvas.removeEventListener('pointerdown', onPointerDown);
    window.removeEventListener('pointerup', onPointerUp);
    effect.destroy?.(state);
  };
}

/**
 * Liquid Metal — Flowing chrome gradient with animated specular highlight streak.
 * Category: backgrounds | Animate: true | Interactive: false | Complexity: medium
 */
const __effect = function liquidMetal(ctx, state) {
  return {
    frame({ width, height, time, reducedMotion }) {
      const t = reducedMotion ? 0 : time;

      // Base chrome gradient — radial center drifts
      const cx = width * 0.5 + Math.sin(t * 0.38) * width * 0.22;
      const cy = height * 0.42 + Math.cos(t * 0.28) * height * 0.14;
      const r = Math.max(width, height) * 0.95;

      const base = ctx.createRadialGradient(cx, cy, 0, cx, cy, r);
      base.addColorStop(0, 'rgba(228, 232, 242, 1)');
      base.addColorStop(0.18, 'rgba(188, 196, 212, 1)');
      base.addColorStop(0.45, 'rgba(128, 138, 158, 1)');
      base.addColorStop(0.75, 'rgba(74,  84, 102, 1)');
      base.addColorStop(1, 'rgba(36,  42,  56, 1)');

      ctx.fillStyle = base;
      ctx.fillRect(0, 0, width, height);

      if (reducedMotion) return;

      // Specular streak — angled band of light
      const sx = width * 0.15 + Math.sin(t * 0.52 + 0.8) * width * 0.65;
      const angle = -0.38 + Math.sin(t * 0.22) * 0.12;
      const bandW = 60 + Math.sin(t * 0.35) * 20;

      ctx.save();
      ctx.translate(sx, 0);
      ctx.rotate(angle);

      const streak = ctx.createLinearGradient(-bandW, 0, bandW, 0);
      streak.addColorStop(0, 'rgba(255,255,255,0)');
      streak.addColorStop(0.35, 'rgba(255,255,255,0.28)');
      streak.addColorStop(0.5, 'rgba(255,255,255,0.55)');
      streak.addColorStop(0.65, 'rgba(255,255,255,0.28)');
      streak.addColorStop(1, 'rgba(255,255,255,0)');

      ctx.fillStyle = streak;
      ctx.fillRect(-bandW, -height, bandW * 2, height * 3);
      ctx.restore();

      // Secondary soft reflection
      const rx = width * 0.72 + Math.cos(t * 0.41 + 2) * width * 0.18;
      const ry = height * 0.3 + Math.sin(t * 0.33 + 1) * height * 0.12;
      const rg = ctx.createRadialGradient(rx, ry, 0, rx, ry, 120);
      rg.addColorStop(0, 'rgba(255,255,255,0.18)');
      rg.addColorStop(0.5, 'rgba(255,255,255,0.06)');
      rg.addColorStop(1, 'rgba(255,255,255,0)');
      ctx.fillStyle = rg;
      ctx.fillRect(0, 0, width, height);
    },
  };
}

const canvas = document.getElementById('canvas-effect');
mountCanvas(canvas, __effect, { animate: true, clear: true });
</script>