Penalty Kick

A penalty-kick mechanic built around a deception trick rather than raw power: the keeper doesn’t know your target, it reads the ball’s position and heading at one reaction instant partway through flight and extrapolates a straight line from there. A curved shot bends after that read — so curling the ball away from its own early trajectory is what beats a keeper who has otherwise “solved” your aim. Straight, hard, and dead-center is honest and easy to save; a bent shot toward a post the ball didn’t look like it was going to reaches goal even against a sharp keeper.

Timed to the 2026 World Cup final having just been played down the road at MetLife Stadium.

Reuse

The mechanic lives in src/penalty-kick.js as a framework-free ES module:

• createShootout(opts) — returns a state object; call update(dt) each frame and shoot(aimX, aimZ, power, curve) to take a shot.
• opts: keeperSkill (0..1, how closely the keeper’s guess tracks the true target vs. the naive straight-line read), keeperReactionT (0..1, fraction of flight before the keeper commits to a dive).
• Field units are normalized: aimX spans -1..1 across the goal mouth, aimZ spans 0..H (cfg.H, the crossbar height); aiming above H skies it automatically. power trades shot speed for keeper reaction time — a faster shot leaves the keeper less time to react and dive, a slower lofted one gives it more. curve (-1..1) bends the ball’s path, not its final landing spot; only the keeper’s early read is fooled.
• State exposes phase (aiming | flight | result), ball (x, z), keeper (x, committed), t, lastOutcome, and score (attempts/goals/saves/misses/streak/bestStreak). Rendering, input, and the charge-power UI are entirely the caller’s job — the demo drives it with mouse-hold-and-drag (hold to charge power, drag sideways while held to add curve).

Port notes for DragonRuby: update() and the trajectory math have no DOM dependencies; ballAt(t, shot) and keeperGuess(t, shot) translate directly into a tick method, with the goal-to-screen mapping owned by the renderer.

Gotchas

• shoot() is a no-op outside phase === 'aiming' — the module resets itself automatically RESULT_HOLD seconds after a result, no caller-side bookkeeping needed.
• The ball’s x(t)/z(t) formulas both return exactly aimX/aimZ at t = 1 regardless of curve or loft — the bend and arc are pure mid-flight bulges (sin(pi·t) terms), so the final target is never affected by how showy the shot looks.
• The demo in demo/ bundles its own copy of the module (self-contained by contract). If you touch src/, re-copy it into demo/.