---
name: physics-press-reaction
description: 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).
metadata:
  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](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

```html
<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>
```

```js
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).
