hyperframes/skills/gsap/references/effects.md

GSAP Effects for HyperFrames

Drop-in animation patterns for HyperFrames compositions. Each effect is self-contained with HTML, CSS, and code.

All effects follow HyperFrames composition rules — deterministic, no randomness, timelines registered via window.__timelines.

Table of Contents

• Typewriter
• Audio Visualizer

---

Typewriter

Reveal text character by character using GSAP's TextPlugin.

Required Plugin

<script src="https://cdn.jsdelivr.net/npm/gsap@3.14.2/dist/gsap.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/gsap@3.14.2/dist/TextPlugin.min.js"></script>
<script>
  gsap.registerPlugin(TextPlugin);
</script>

Basic Typewriter

const text = "Hello, world!";
const cps = 10; // chars per second: 3-5 dramatic, 8-12 conversational, 15-20 energetic
tl.to(
  "#typed-text",
  { text: { value: text }, duration: text.length / cps, ease: "none" },
  startTime,
);

With Blinking Cursor

Three rules:

1. One cursor visible at a time — hide previous before showing next.
2. Cursor must blink when idle — after typing, during pauses.
3. No gap between text and cursor — elements must be flush in HTML.

<span id="typed-text"></span><span id="cursor" class="cursor-blink">|</span>

@keyframes blink {
  0%,
  100% {
    opacity: 1;
  }
  50% {
    opacity: 0;
  }
}
.cursor-blink {
  animation: blink 0.8s step-end infinite;
}
.cursor-solid {
  animation: none;
  opacity: 1;
}
.cursor-hide {
  animation: none;
  opacity: 0;
}

Pattern: blink → solid (typing starts) → type → solid → blink (typing done).

tl.call(() => cursor.classList.replace("cursor-blink", "cursor-solid"), [], startTime);
tl.to("#typed-text", { text: { value: text }, duration: dur, ease: "none" }, startTime);
tl.call(() => cursor.classList.replace("cursor-solid", "cursor-blink"), [], startTime + dur);

Backspacing

TextPlugin removes from front — wrong for backspace. Use manual substring removal:

function backspace(tl, selector, word, startTime, cps) {
  const el = document.querySelector(selector);
  const interval = 1 / cps;
  for (let i = word.length - 1; i >= 0; i--) {
    tl.call(
      () => {
        el.textContent = word.slice(0, i);
      },
      [],
      startTime + (word.length - i) * interval,
    );
  }
  return word.length * interval;
}

Spacing with Static Text

When a typewriter word sits next to static text, use margin-left on a wrapper span. Don't use flex gap (spaces cursor from text) or trailing space in static text (collapses when dynamic is empty).

<div style="display:flex; align-items:baseline;">
  <span style="font-size:40px; color:#555;">Ship something</span>
  <span style="margin-left:14px;"><span id="word"></span><span id="cursor">|</span></span>
</div>

Word Rotation

Type → hold → backspace → next word. Cursor blinks during every idle moment (holds, after backspace).

words.forEach((word, i) => {
  const typeDur = word.length / 10;
  // Solid while typing
  tl.call(() => cursor.classList.replace("cursor-blink", "cursor-solid"), [], offset);
  tl.to("#typed-text", { text: { value: word }, duration: typeDur, ease: "none" }, offset);
  // Blink during hold
  tl.call(() => cursor.classList.replace("cursor-solid", "cursor-blink"), [], offset + typeDur);
  offset += typeDur + 1.5; // hold

  if (i < words.length - 1) {
    tl.call(() => cursor.classList.replace("cursor-blink", "cursor-solid"), [], offset);
    const clearDur = backspace(tl, el, word, offset, 20);
    tl.call(() => cursor.classList.replace("cursor-solid", "cursor-blink"), [], offset + clearDur);
    offset += clearDur + 0.3;
  }
});

Appending Words

Build a sentence word-by-word into the same element:

let accumulated = "";
words.forEach((word) => {
  const target = accumulated + (accumulated ? " " : "") + word;
  const newChars = target.length - accumulated.length;
  tl.to("#typed-text", { text: { value: target }, duration: newChars / 10, ease: "none" }, offset);
  accumulated = target;
  offset += newChars / 10 + 0.3;
});

Multi-Line Cursor Handoff

When handing off between typewriter lines: hide previous → blink new → pause → solid when typing. Never go hidden→solid (skips idle state).

tl.call(
  () => {
    prevCursor.classList.replace("cursor-blink", "cursor-hide");
    nextCursor.classList.replace("cursor-hide", "cursor-blink");
  },
  [],
  handoffTime,
);

const typeStart = handoffTime + 0.5; // brief blink pause
tl.call(() => nextCursor.classList.replace("cursor-blink", "cursor-solid"), [], typeStart);
tl.to("#next-text", { text: { value: text }, duration: dur, ease: "none" }, typeStart);
tl.call(() => nextCursor.classList.replace("cursor-solid", "cursor-blink"), [], typeStart + dur);

Timing Guide

CPS	Feel	Good for
3-5	Slow, deliberate	Dramatic reveals, suspense
8-12	Natural typing	Dialogue, narration
15-20	Fast, energetic	Tech demos, code
30+	Near-instant	Filling long blocks

---

Audio Visualizer

Pre-extract audio data, drive canvas/DOM rendering from GSAP timeline.

Extract Audio Data

python scripts/extract-audio-data.py audio.mp3 -o audio-data.json
python scripts/extract-audio-data.py video.mp4 --fps 30 --bands 16 -o audio-data.json

Requires ffmpeg and numpy.

Data Format

{
  "fps": 30, "totalFrames": 5415,
  "frames": [{ "time": 0.0, "rms": 0.42, "bands": [0.8, 0.6, 0.3, ...] }]
}

• rms (0-1): overall loudness, normalized across track
• bands[] (0-1): frequency magnitudes. Index 0 = bass, higher = treble. Each normalized independently.

Loading the Data

// Option A: inline (small files, under ~500KB)
const AUDIO_DATA = {
  /* paste audio-data.json contents */
};
setupTimeline(AUDIO_DATA);

// Option B: fetch (large files)
fetch("audio-data.json")
  .then((r) => r.json())
  .then((data) => setupTimeline(data));

function setupTimeline(AUDIO_DATA) {
  // IMPORTANT: all tl.call() setup must be inside this callback
  for (let f = 0; f < AUDIO_DATA.totalFrames; f++) {
    tl.call(() => draw(AUDIO_DATA.frames[f]), [], f / AUDIO_DATA.fps);
  }
}

With fetch, wrap all timeline setup inside the callback so AUDIO_DATA is available.

Rendering Approaches

Canvas 2D (most common — bars, waveforms, circles, gradients):

for (let f = 0; f < AUDIO_DATA.totalFrames; f++) {
  tl.call(
    () => {
      const frame = AUDIO_DATA.frames[f];
      ctx.clearRect(0, 0, canvas.width, canvas.height);
      // draw using frame.rms and frame.bands
    },
    [],
    f / AUDIO_DATA.fps,
  );
}

WebGL / Three.js — HyperFrames patches THREE.Clock for deterministic time. Update uniforms from audio data each frame.

DOM Elements — fine for < 20 elements, less performant than Canvas for many.

Spatial Mapping

• Horizontal: bass left, treble right (iterate bands left-to-right)
• Vertical: bass bottom, treble top
• Circular: bass at 12 o'clock, wrap clockwise; mirror for full circle

Smoothing

let prev = null;
const smoothing = 0.25; // 0.1-0.2 snappy, 0.3-0.5 flowing
function smooth(f) {
  const raw = AUDIO_DATA.frames[f];
  if (!prev) {
    prev = { rms: raw.rms, bands: [...raw.bands] };
    return prev;
  }
  prev = {
    rms: prev.rms * smoothing + raw.rms * (1 - smoothing),
    bands: raw.bands.map((b, i) => prev.bands[i] * smoothing + b * (1 - smoothing)),
  };
  return prev;
}

Motion Principles

• Bass drives big moves — scale, glow, position shifts
• Treble drives detail — shimmer, flicker, edge effects
• RMS drives globals — background brightness, overall energy
• Pick 2-3 properties to animate. More looks noisy.
• Keep minimums above zero — quiet sections need life.

Band Count

Bands	Detail	Good for
4	Low	Background glow, pulsing
8	Medium	Bar charts, basic spectrum
16	High	Detailed EQ (default)
32	Very high	Dense radial layouts

Layering

Layer multiple canvases with CSS z-index for depth — a background layer driven by bass/rms and a foreground layer driven by individual bands creates depth without complexity.

<canvas id="bg-layer" style="position:absolute;top:0;left:0;z-index:1;"></canvas>
<canvas id="main-layer" style="position:absolute;top:0;left:0;z-index:2;"></canvas>