chore: import upstream snapshot with attribution

2026-07-13 12:58:35 +08:00
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+---
+name: discrete-text-sequence
+description: Replace entire text states at frame thresholds for non-linear typing effects — typos, bulk additions, pauses, backspaces, simulated thinking.
+metadata:
+  tags: text, typing, discrete, threshold, non-linear, sequence
+---
+
+# Discrete Text Sequence
+
+Instead of character-by-character typewriter, replace entire string states at time thresholds. Enables non-linear effects (typos, bulk additions, pauses, "thinking" gaps) that smooth per-char typing can't achieve.
+
+## How It Works
+
+An array of `{ text, t }` pairs where `t` is a time in seconds. On every onUpdate, scan the array for the latest entry whose `t` has passed and render that text. The display jumps between states; no animation between them.
+
+For continuous per-char typewriter (no pauses, no edits), use the **smooth-slice** variation at the bottom.
+
+## HTML
+
+```html
+<div
+  class="scene"
+  id="seq-scene"
+  data-composition-id="seq-scene"
+  data-start="0"
+  data-duration="6"
+  data-track-index="0"
+>
+  <div class="terminal">
+    <div class="prompt">$</div>
+    <div class="text-wrap">
+      <span class="text" id="text">|</span>
+      <span class="cursor" id="cursor">_</span>
+    </div>
+  </div>
+</div>
+```
+
+## CSS
+
+```css
+.scene {
+  position: relative;
+  width: 100%;
+  height: 100%;
+  display: grid;
+  place-items: center;
+  background: {bgColor};
+  font-family: {monoFont}; /* monospace is required — see Critical Constraints */
+}
+.terminal {
+  display: flex;
+  align-items: baseline;
+  gap: GUTTER;
+  font-weight: 800;
+  font-size: TERMINAL_FONT_SIZE;
+  color: {textColor};
+}
+.prompt {
+  color: {accentColor};
+}
+.text-wrap {
+  display: inline-flex;
+  align-items: baseline;
+  /* Fixed-width container prevents the right side from jittering as
+     content changes length. Choose width ≥ longest state's width. */
+  min-width: TEXT_WRAP_MIN_WIDTH;
+  white-space: nowrap;
+}
+.text {
+  color: {textColor};
+}
+.cursor {
+  display: inline-block;
+  width: CURSOR_WIDTH;
+  color: {accentColor};
+  margin-left: CURSOR_GAP;
+}
+```
+
+## GSAP Timeline + Discrete State Logic
+
+```html
+<script src="https://cdn.jsdelivr.net/npm/gsap@3.14.2/dist/gsap.min.js"></script>
+<script>
+  window.__timelines = window.__timelines || {};
+
+  // SEQUENCE — each entry shows from t to the NEXT entry's t.
+  // Non-linear: typos, corrections, bulk additions, pauses.
+  // Shape (one realization):
+  //   [warm-up keystrokes] → [typo] → [backspaces back to fork] →
+  //   [bulk-paste of the corrected continuation] → [completion mark]
+  const SEQUENCE = [
+    { t: 0.0, text: "" },
+    { t: T_K1, text: "{p1}" }, // first keystrokes (~3-5 chars, 0.1-0.2s apart)
+    { t: T_K2, text: "{p1 + ' ' + p2_typo}" }, // continuation containing a typo
+    { t: T_BS, text: "{p1 + ' ' + p2_partial}" }, // backspace(s) — peel back to the fork
+    { t: T_BULK, text: "{fullCorrectedText}" }, // bulk paste — replaces several chars at once
+    { t: T_DONE, text: "{fullCorrectedText + ' ✓'}" }, // completion marker
+  ];
+
+  // Reverse-search for the latest entry whose t has passed.
+  function textAt(time) {
+    for (let i = SEQUENCE.length - 1; i >= 0; i--) {
+      if (time >= SEQUENCE[i].t) return SEQUENCE[i].text;
+    }
+    return "";
+  }
+
+  const textEl = document.getElementById("text");
+  const cursorEl = document.getElementById("cursor");
+  const tl = gsap.timeline({ paused: true });
+
+  // Drive the discrete display via a 0→TOTAL_DURATION tween's onUpdate
+  const driver = { t: 0 };
+  tl.to(
+    driver,
+    {
+      t: TOTAL_DURATION,
+      duration: TOTAL_DURATION,
+      ease: "none",
+      onUpdate: () => {
+        textEl.textContent = textAt(driver.t);
+      },
+    },
+    0,
+  );
+
+  // Cursor blink — deterministic via sin, not CSS animation
+  const blinkDriver = { p: 0 };
+  tl.to(
+    blinkDriver,
+    {
+      p: Math.PI * 2 * BLINK_CYCLES, // BLINK_CYCLES = blinks across composition
+      duration: TOTAL_DURATION,
+      ease: "none",
+      onUpdate: () => {
+        cursorEl.style.opacity = Math.sin(blinkDriver.p) > 0 ? "1" : "0";
+      },
+    },
+    0,
+  );
+
+  window.__timelines["seq-scene"] = tl;
+</script>
+```
+
+## Variations
+
+### Smooth character slice (continuous typewriter — no pauses, no edits)
+
+For straight-forward typewriter without the non-linear chaos:
+
+```js
+const fullText = "{fullPhrase}";
+const len = { v: 0 };
+tl.to(
+  len,
+  {
+    v: fullText.length,
+    duration: TYPE_DUR,
+    ease: "power1.inOut",
+    onUpdate: () => {
+      textEl.textContent = fullText.substring(0, Math.floor(len.v));
+    },
+  },
+  0,
+);
+```
+
+This is faster to author but produces a uniform "machine-typed" feel — missing the human-typing realism.
+
+### Thinking pause (extended hold on a key state)
+
+Insert a state that holds for `THINK_HOLD_DUR` seconds without changes — feels like the user paused to think:
+
+```js
+{ t: T_PRE_PAUSE, text: '{partialPhrase}' },        // last state before the pause
+// ... no entries for THINK_HOLD_DUR seconds ...
+{ t: T_PRE_PAUSE + THINK_HOLD_DUR, text: '{resumedPhrase}' },
+```
+
+### State pulse on completion
+
+When the final state lands (e.g. "✓"), pulse-scale the line briefly for emphasis:
+
+```js
+tl.to(
+  ".text",
+  { scale: COMPLETION_PULSE_SCALE, duration: COMPLETION_PULSE_DUR, yoyo: true, repeat: 1 },
+  T_DONE,
+);
+```
+
+### Per-state color shift
+
+Color-code states by phase (e.g. dim during edit, success color after the completion marker, optional warning color on typo):
+
+```js
+// In onUpdate after setting textContent:
+if (driver.t > T_DONE) textEl.style.color = "{successColor}";
+else if (driver.t < T_K2)
+  textEl.style.color = "{textColor}"; // normal typing
+else textEl.style.color = "{mutedColor}"; // mid-edit dim
+```
+
+## How to Choose Values
+
+### Layout
+
+- **TERMINAL_FONT_SIZE** — font size of the typing line.
+  - Range: 48-96 px for full-bleed compositions; smaller for terminal-style detail
+  - Constraints: combined with `TEXT_WRAP_MIN_WIDTH` must fit within viewport
+- **TEXT_WRAP_MIN_WIDTH** — fixed-width container holding the text.
+  - Constraints: must be `≥ widthOf(longest SEQUENCE state) at TERMINAL_FONT_SIZE`. Measure with a hidden probe after `document.fonts.ready` if unsure
+  - Effects: too small → right edge jitters as states change length; too large → unused horizontal whitespace pads the composition
+- **GUTTER** — flex gap between prompt glyph (`$`, `>`) and text.
+  - Range: ~0.3-0.5× `TERMINAL_FONT_SIZE`
+- **CURSOR_WIDTH / CURSOR_GAP** — block cursor dimensions.
+  - Range: width ~0.3× `TERMINAL_FONT_SIZE`; gap small (single-digit px) so the cursor feels attached to the text
+
+### Sequence timing
+
+- **TOTAL_DURATION** — composition length.
+  - Constraints: must be ≥ `T_DONE` + ~1s climax dwell so viewer sees the completion marker
+- **T_K1 / T_K2 / T_BS / T_BULK / T_DONE** — milestone timestamps within the SEQUENCE.
+  - Range: keystrokes 0.06-0.20s apart for "human typing"; pauses 0.3-0.6s at natural word breaks; bulk paste jumps multiple characters in a single entry
+  - Constraints: monotonically increasing; `T_DONE ≤ TOTAL_DURATION - dwell`
+- **TYPE_DUR** (smooth-slice variation) — total typing duration for continuous typewriter.
+  - Range: `chars × 0.06s` (fast) to `chars × 0.12s` (relaxed)
+- **THINK_HOLD_DUR** (thinking-pause variation) — hold time between two SEQUENCE states.
+  - Range: 0.8-2.0s; under 0.5s reads as a stutter rather than thought
+- **COMPLETION_PULSE_SCALE / COMPLETION_PULSE_DUR** (pulse variation).
+  - Range: scale 1.03-1.08 (subtle), duration 0.15-0.30s
+
+### Cursor
+
+- **BLINK_CYCLES** — number of full blink cycles across `TOTAL_DURATION`.
+  - Range: `TOTAL_DURATION / 0.8s ≤ BLINK_CYCLES ≤ TOTAL_DURATION / 0.5s` (cycle every 0.5-0.8s reads as a natural cursor)
+
+### Color tokens
+
+- **{bgColor} / {textColor} / {accentColor} / {successColor} / {mutedColor}** — discrete choices, not numeric ranges. Pick from the composition's palette; the prompt + cursor share `{accentColor}` so they read as the same "system" element.
+
+## Key Principles
+
+- **Threshold sequence drives realism** — group fast successive keystrokes (0.1-0.2s apart), then pause on word breaks (0.3-0.5s), bulk-paste in single jumps (one entry replaces many chars), include a typo or two for human-typing feel
+- **Reverse-search the array each frame** — O(n) per frame, where n is small (≤30 typical). Don't try to index by frame; the sequence is sparse
+- **Fixed-width container is mandatory** — without `min-width`, the right edge of the text wrap jitters as state length changes. Set width ≥ longest expected state
+- **Cursor must be deterministic** — sin-based or sequence-driven blink, NOT a CSS animation. HF seeks frame-by-frame; CSS animations desync
+- **No `transition` on the text element** — discrete jumps should be INSTANT. A CSS transition turns the jump into a smear and ruins the "typing" feel
+- **❗ Distinguish discrete from smooth** — if your effect is "type each character, no edits" → use the smooth-slice variation. Discrete sequence is overkill for that case. Use discrete only when you need non-linear states (typos, pauses, bulk paste)
+
+## Critical Constraints
+
+- **Timeline must be paused**: `gsap.timeline({ paused: true })`
+- **Registry key = `data-composition-id`**
+- **No CSS `transition`** on the text or any of its parents
+- **Cursor `display: inline-block`** — `display: inline` ignores width/transform
+- **Monospace font** for terminal-style effects — proportional fonts cause visual jitter even with fixed-width container
+- **Whitespace: nowrap** on text wrap — wrapping mid-state breaks the illusion
+
+## Combinations
+
+- [3d-text-depth-layers.md](3d-text-depth-layers.md) — discrete text rendered with layered depth (heavy, dramatic)
+- [counting-dynamic-scale.md](counting-dynamic-scale.md) — discrete text for the LABEL while counter animates smoothly
+- [press-release-spring.md](press-release-spring.md) — after the sequence completes, the line "presses" like a button confirming success
+
+## Pairs with HF skills
+
+- `/hyperframes-animation` — onUpdate-driven discrete state lookup
+- `/hyperframes-core` — composition wiring
+- `/hyperframes-cli` — `hyperframes lint`