frames/skills/frames-animation/rules/vertical-spring-ticker.md

name, description, metadata

name	description	metadata
vertical-spring-ticker	Slot-machine style vertical scrolling using additive spring physics within a masked container — each spring contributes one "step" of scroll.	tags text, ticker, spring, scroll, vertical, slot-machine, sequence

Vertical Spring Ticker (Slot Machine)

Multiple spring tweens are ADDED TOGETHER to produce total Y translation — each spring contributes one discrete "step", so instead of a single linear scroll you get the slot-machine "click click click" rhythm with natural settling. Distinct from a continuous marquee: this rule's semantics are discrete steps that land; for endless linear motion see sine-wave-loop.md.

How It Works

A masked window of fixed height ITEM_HEIGHT (overflow: hidden) holds a vertical stack of items, each exactly ITEM_HEIGHT tall. Each spring holds a 0→1 progress; a shared onUpdate sums them and applies translateY(-sum × ITEM_HEIGHT). Springs fire sequentially with overlap (STEP_SPACING ≤ STEP_DUR), so each step snaps in while the previous is still settling — that overlap is what makes them additive, and the back.out overshoot is what makes each step read as a "click".

Recipe

<!-- inside a standard scene clip (frames-core) -->
<div class="ticker" id="ticker">
  <div class="stack-inner" id="stack-inner">
    <div class="item">{item0}</div>
    <div class="item">{item1}</div>
    <div class="item">{itemN}</div>
  </div>
</div>

.ticker {
  width: TICKER_WIDTH;
  height: ITEM_HEIGHT; /* MUST match .item height exactly */
  overflow: hidden; /* the mask is the window */
}
.stack-inner {
  display: flex;
  flex-direction: column; /* mandatory — vertical stacking */
}
.item {
  height: ITEM_HEIGHT; /* MUST equal .ticker height */
  display: flex;
  align-items: center;
  justify-content: center;
  /* font-variant-numeric: tabular-nums; — for numeric tickers */
}

const innerEl = document.getElementById("stack-inner");
const springs = Array.from({ length: STEPS }, () => ({ p: 0 }));

function applyTransform() {
  const sumP = springs.reduce((acc, s) => acc + s.p, 0);
  innerEl.style.transform = `translateY(${-sumP * ITEM_HEIGHT}px)`;
}
applyTransform(); // initial state

springs.forEach((spring, i) => {
  tl.to(
    spring,
    {
      p: 1,
      duration: STEP_DUR,
      ease: `back.out(${BOUNCE_FACTOR})`,
      onUpdate: applyTransform,
    },
    STEP_START + i * STEP_SPACING,
  );
});

Variations

• Numeric ticker (price / counter rolling) — items are the digit sequence; run the same spring-step pattern per decimal position. font-variant-numeric: tabular-nums required.
• Reverse direction (countdown) — flip the sign (translateY(${sumP * ITEM_HEIGHT}px)) and arrange items in reverse order.
• Pause between groups — several fast steps (small STEP_SPACING), a long pause, then one dramatic final step with a bigger BOUNCE_FACTOR. The pause is where the eye locks in.
• Continuous infinite ticker — NOT this rule (this rule is discrete steps); a looping news ticker is a single linear tween with duplicated items — see sine-wave-loop.md for continuous-motion semantics.

Values

token	range	notes
ITEM_HEIGHT	~fontSize × 1.25	must hold capital descenders; .ticker height MUST equal it exactly
TICKER_WIDTH	30–60% viewport width	wide enough for the longest item without ellipsis
STEPS	1–4	number of transitions, not items; STEPS ≤ itemCount − 1
STEP_DUR	0.3–0.7s	under 0.3 the overshoot is invisible; over 0.7 the click reads as a slide
STEP_SPACING	0.3–0.5s	≤ STEP_DUR so springs overlap (additive); wider gaps read as a lazy linear scroll
BOUNCE_FACTOR	1.4–2.5	1.4 gentle click / 2.0 firm / 2.5+ casino spin-and-land for a climax step

Reference: ../../examples/proof-logo-chain.html (204px, 1 step, 0.45s).

Critical Constraints

• Container height = item height, pixel-exact, all items equal — mismatches show partial item edges above/below the mask and accumulate drift across steps.
• overflow: hidden on the container, not the inner stack; flex-direction: column on the stack.
• Sum the springs in onUpdate — never tween the final position directly. Each spring contributing its OWN snap is the slot-machine pacing.
• Overlap steps and keep back.out per step — non-overlapping steps or an out-only ease collapse into a linear scroll.
• Never update items via innerHTML between steps — the ticker moves the SAME items via translate; swapping content shows the previous item AS the new one (broken illusion).
• Climax dwell ≥1s after the final step (SKILL universal constraint).
• tabular-nums for numeric tickers — variable digit widths break alignment.

See also

reactive-displacement (ticker pushed by an incoming element) · scale-swap-transition (ticker scales out after settling) · press-release-spring (button press triggers the spin).