game-feel

SKILL.md

Game feel (juice)

The difference between a mechanic that works and one that feels good is feedback: the
layered, slightly-exaggerated response an action provokes. This skill covers the engine-
neutral techniques — screen shake, hit-stop, easing, squash & stretch, knockback, and stacked
feedback — and tells you how to apply them without burying the underlying simulation. It
adds polish on top of an existing mechanic; it does not implement the mechanic.

When to use

Use when an action (hit, jump, dash, pickup, death, button press) is mechanically correct
but feels weak, weightless, or unsatisfying, and you want it to feel responsive and punchy.

Use to add screen shake, hit-stop/freeze frames, eased motion, squash & stretch, knockback,
flashes, or to layer multiple feedback channels onto one event.

Use to decide how much juice is enough and where it crosses into noise.

When not to use: for the raw controller math (jump height, coyote time) use the
platformer genre and the engine movement skill. For camera follow/deadzone/orbit framing
use camera-systems (this skill only triggers the shake). For mixing, ducking, and adaptive
music use audio-design. For shader-based dissolves/flashes use shader-programming and the
engine shader skill. For the concrete tween/particle node APIs, use the engine animation skill
(godot-animation, unity-animation).

Core principle: feedback is layered and exaggerated

One satisfying hit is usually 5–8 tiny responses firing together within ~100 ms: a sound,
a particle burst, a brief hit-stop, a flash, a knockback, a small screen shake, and a number
popping up. Each is cheap; stacked, they read as "impact". Two rules keep it from becoming a
mess: (1) exaggerate briefly and return to rest (juice is transient, not a new resting
state); (2) scale juice to event importance — a footstep is not a boss death.

Core workflow

Confirm the event hooks exist. Juice attaches to discrete events: on_hit, on_land,
on_pickup, on_death, on_fire. If the mechanic doesn't emit these, add them first.

Pick feedback channels per event from the menu (sound, particles, shake, hit-stop,
flash, knockback, tween, number pop). Start with 2–3; add until it reads, then stop.

Make motion eased, not linear. Route scale/position/UI changes through a tween with an
ease (overshoot for "pop", ease-out for "settle"). Linear motion feels robotic.

Reserve hit-stop and shake for impact. They are the strongest, most abusable tools —
short durations, scaled to importance, and never on routine actions.

Keep feedback off the critical simulation. Shake moves the camera/visual, not the
body; hit-stop uses time scale or a real-time pause, not a gameplay-logic stall.

Tune by importance tiers. Define small/medium/large feedback presets and assign events
to a tier, so the whole game's juice stays consistent and proportional.

Verify by playing and watching. Trigger the event repeatedly; confirm the feedback
fires, returns to rest, and is not nauseating or input-blocking. Report what you observed
(does shake decay? does input still register during hit-stop?).

Patterns

1. Screen shake by decaying "trauma" (smooth, not a random jitter)

# Godot 4.7. Store trauma 0..1; shake = trauma^2 so small hits barely move, big hits punch.
# Drives a Camera2D OFFSET (the visual), never the player body. Decays every frame.
@export var decay := 1.2          # trauma lost per second
@export var max_offset := Vector2(12, 8)
@export var max_roll := 0.1       # radians
var trauma := 0.0
var _t := 0.0

func add_trauma(amount: float) -> void:
    trauma = clampf(trauma + amount, 0.0, 1.0)   # hits ADD; they don't reset

func _process(dt: float) -> void:
    if trauma <= 0.0: return
    trauma = maxf(trauma - decay * dt, 0.0)
    var shake := trauma * trauma                  # quadratic: gentle low, sharp high
    _t += dt * 30.0
    # Smooth pseudo-random via sampled noise/sin, NOT rand each frame (that buzzes).
    offset = Vector2(max_offset.x * shake * sin(_t * 1.7),
                     max_offset.y * shake * sin(_t * 2.3))
    rotation = max_roll * shake * sin(_t * 1.1)
# Unity 6.3 LTS: identical model on a CinemachineCamera via CinemachineBasicMultiChannelPerlin
# (set AmplitudeGain/FrequencyGain from trauma^2) — see camera-systems.

2. Hit-stop / freeze frame (sell impact by briefly stopping time)

# Godot 4.7. Drop time scale, then restore after a REAL-TIME delay (unaffected by time_scale).
func hit_stop(duration := 0.08, scale := 0.05) -> void:
    Engine.time_scale = scale
    # 4th arg ignore_time_scale=true → the timer still fires while the game is frozen.
    await get_tree().create_timer(duration, true, false, true).timeout
    Engine.time_scale = 1.0

// Unity 6.3 LTS (C#). WaitForSecondsRealtime ignores Time.timeScale, so the timer still elapses.
IEnumerator HitStop(float duration = 0.08f, float scale = 0.05f) {
    Time.timeScale = scale;
    yield return new WaitForSecondsRealtime(duration);
    Time.timeScale = 1f;            // RIGHT: real-time wait. WRONG: WaitForSeconds (never resumes at scale 0)
}

3. Squash & stretch + overshoot via an eased tween (the "pop")

# Godot 4.7. Conserve volume: stretch one axis, squash the other, then spring back with overshoot.
func pop(node: Node2D) -> void:
    node.scale = Vector2(1.3, 0.7)                       # instant squash on the event
    var tw := create_tween()
    tw.tween_property(node, "scale", Vector2.ONE, 0.18) \
      .set_trans(Tween.TRANS_BACK).set_ease(Tween.EASE_OUT)   # BACK = overshoots past 1, settles
# RIGHT: ease back (TRANS_BACK/ELASTIC) for life. WRONG: linear tween → mechanical, dead.

4. A feedback bundle scaled by importance (keep juice proportional)

# One call per event; the tier decides intensity so the whole game stays consistent.
func feedback(event_pos: Vector2, tier: String) -> void:
    match tier:
        "small":  AudioBus.play("tick");  Camera.add_trauma(0.15)
        "medium": AudioBus.play("hit");   Camera.add_trauma(0.4);  hit_stop(0.05); spawn_particles(event_pos, 6)
        "large":  AudioBus.play("boom");  Camera.add_trauma(0.8);  hit_stop(0.12); spawn_particles(event_pos, 30); flash_white(0.06)

Pitfalls

Shaking the player/body instead of the camera offset desyncs collision and aim. Shake
the camera (or a visual pivot), never the simulated transform.

Random offset every frame buzzes like static. Drive shake from sampled noise/sin and a
decaying trauma value so it's smooth and self-ending.

Hit-stop with WaitForSeconds / a scaled timer never resumes (at time scale 0 the timer
never advances). Use a real-time wait (WaitForSecondsRealtime, or Godot's
ignore_time_scale timer).

Hit-stop on every frame of a held attack locks the game. Trigger it once per impact.

Linear tweens everywhere feel robotic. Ease almost everything; reserve overshoot
(BACK/ELASTIC) for "pop" and ease-out for "settle".

Permanent exaggeration (scale never returns, shake never decays) becomes the new normal
and stops reading as feedback. Juice must return to rest.

Over-juicing routine actions (full shake + hit-stop on every footstep) causes nausea and
hides real impacts. Scale to importance; add a "reduce screen shake"/"reduce flashing"
accessibility option.

Feedback that blocks input (long freeze, un-cancelable animation) hurts responsiveness.
Keep juice short and let input buffer through it.

References

For the trauma-shake math, easing-curve cheat sheet (which ease for pop vs settle), knockback

flash + number-pop recipes, importance-tier presets, and per-engine tween/particle bindings,
read references/feedback-recipes.md.

Related skills

camera-systems — owns camera follow/deadzone/orbit; this skill only feeds it shake trauma.

godot-animation, unity-animation — concrete tween/AnimationPlayer/particle APIs juice rides on.

audio-design — the sound layer of every feedback bundle; ducking and SFX variation.

physics-tuning — knockback forces and the timestep juice must not destabilize.

platformer, fps-shooter, roguelike — genres whose moment-to-moment feel this elevates.