frames/skills/frames-animation/rules/physics-press-reaction.md

name, description, metadata

name	description	metadata
physics-press-reaction	Cursor + element synchronized press via subtractive spring forces — cursor lands on element, both compress together, then release. Distinct from press-release-spring (which has no cursor).	tags spring, click, physics, cursor, subtractive, interaction, synchronized

Physics Press Reaction (Cursor + Element Synced)

Models a real click: a cursor approaches a button, lands, and both compress IN SYNC, then release together. Distinct from press-release-spring.md (no cursor — just a press happening); this rule is the COMBINED cursor + element behavior. A single PRESS_INTENSITY drives both: press down compresses both to 1 - PRESS_INTENSITY via one targets array, release springs both back to 1.0 with overshoot. The cursor translates to the button's center BEFORE the press starts; after release it may move on or hold.

Recipe

<button class="btn" id="btn">{ctaCopy}</button>
<!-- Cursor at scene-root level so it translates freely; arrow TIP is the click
     point, so transform-origin: 0 0 — scaling around the tip keeps it stable. -->
<svg class="cursor" id="cursor" style="pointer-events: none; transform-origin: 0 0">…</svg>

gsap.set("#cursor", { x: CURSOR_START_X, y: CURSOR_START_Y }); // off-screen / far corner

// Phase 1 — approach
tl.to(
  "#cursor",
  { x: BUTTON_CENTER_X, y: BUTTON_CENTER_Y, duration: APPROACH_DUR, ease: "power2.inOut" },
  APPROACH_START,
);

// Phase 2 — coordinated press down: ONE targets array, same scale
tl.to(
  ["#btn", "#cursor"],
  { scale: 1 - PRESS_INTENSITY, duration: PRESS_DOWN_DUR, ease: "power1.in" },
  PRESS_DOWN_AT,
);

// Phase 3 — release: both spring back together
tl.to(
  ["#btn", "#cursor"],
  { scale: 1, duration: RELEASE_DUR, ease: `back.out(${BOUNCE_FACTOR})` },
  RELEASE_AT,
);

// Phase 4 — inner glow during press, resting shadow on release (contact confirmation)
tl.to(
  "#btn",
  { boxShadow: "{btnPressedShadow}", duration: PRESS_DOWN_DUR, ease: "power1.in" },
  PRESS_DOWN_AT,
);
tl.to(
  "#btn",
  { boxShadow: "{btnRestingShadow}", duration: RELEASE_DUR, ease: "power2.out" },
  RELEASE_AT,
);

// Cursor optionally exits after the press settles
tl.to(
  "#cursor",
  { x: CURSOR_EXIT_X, y: CURSOR_EXIT_Y, duration: CURSOR_EXIT_DUR, ease: "power2.out" },
  CURSOR_EXIT_AT,
);

Variations

• Multiple-element chain press — press button A → A triggers a swap → cursor moves to button B → presses again; each press is one full down-release sub-routine.
• Hold press (continuous pressure) — insert a HOLD_DUR window between press-down and release: both scales stay at 1 - PRESS_INTENSITY, inner glow stays on. Suggests "thinking" or "loading."
• Synchronized inner-glow pulse — during the hold, pulse the inset glow with a sine driver: a { p: 0 } proxy tweened to Math.PI * GLOW_PULSE_CYCLES * 2 on ease: "none", onUpdate writing boxShadow with alpha = GLOW_BASE_ALPHA + sin(p) * GLOW_PULSE_AMP. Suggests "processing."

Values

token	range / rule	notes
APPROACH_START	0–0.3 s	long delays read as a dead frame
APPROACH_DUR	0.7–1.3 s	faster = urgent, slower = deliberate
PRESS_DOWN_AT	= APPROACH_START + APPROACH_DUR	cursor arrives exactly as the press begins — avoids "tapping on air"
PRESS_DOWN_DUR	0.1–0.25 s
RELEASE_AT	> PRESS_DOWN_AT + PRESS_DOWN_DUR	optional 0.05–0.4 s hold (or HOLD_DUR 0.3–0.8 s) for "thinking" interactions
RELEASE_DUR	0.4–0.7 s	long enough for the overshoot to settle
PRESS_INTENSITY	0.05 subtle · 0.10 standard · 0.15 heavy	applied to both cursor and button via the single targets array
BOUNCE_FACTOR	1.6 soft · 2.0 firm · 2.4 cartoony
CURSOR_START / EXIT	off-screen or far corner	the approach must read as motion-in, not a teleport; exit ≥ RELEASE_AT + RELEASE_DUR
BUTTON_CENTER	measured	for place-items: center at 1920×1080: (960, 540)
BRAND_REVEAL_AT	< PRESS_DOWN_AT	context precedes interaction
glow pulse	1–4 cycles; base α 0.15–0.3; amp 0.1–0.2	GLOW_BASE_ALPHA − GLOW_PULSE_AMP ≥ 0
CURSOR_SIZE	48–96 px at 1080p

Critical Constraints

• Same press scale on cursor AND button (one targets array) — only the button scaling makes the cursor "tap on air"; only the cursor scaling makes the button feel disconnected.
• Cursor arrives BEFORE the press starts — a clear "cursor over target" moment, or the press is unattributed.
• back.out(BOUNCE_FACTOR) on the release, for both together — a linear release loses the tactile feel; release MUST come after press.
• Inner glow appears DURING press, fades on release — outer shadow shrinks (pushed in), inner glow appears (energy concentrated).
• Cursor transform-origin: 0 0 — the arrow's tip is the click point; scale around the tip keeps it stable. pointer-events: none on the cursor.
• Climax dwell ≥ 1 s — after release the composition must continue ≥ 1 s; the press is a beat, the viewer needs time to see the result.
• No real mouseenter / click events — HF is a render context; everything runs via the timeline.

See also

press-release-spring (the BUTTON-only press; this rule layers the cursor on top) · cursor-click-ripple (adds a ripple at the click point) · scale-swap-transition (the press TRIGGERS the swap).