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

1. 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.
2. 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.
3. 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.
4. Reserve hit-stop and shake for impact. They are the strongest, most abusable tools — short durations, scaled to importance, and never on routine actions.
5. 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.
6. 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.
7. 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.
# Camera2D.ignore_rotation defaults to true, so set it false or the roll does nothing.
@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); for one-off impacts, CinemachineImpulseSource
# on the hitter + CinemachineImpulseListener on the camera — 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).
var _hit_stop_id := 0

func hit_stop(duration := 0.08, slow := 0.05) -> void:
    _hit_stop_id += 1
    var my_id := _hit_stop_id
    Engine.time_scale = slow
    # 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
    if my_id == _hit_stop_id:       # a newer hit-stop owns the restore; don't cut it short
        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 slow = 0.05f) {
    Time.timeScale = slow;
    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.
• Overlapping hit-stops (two hits 30 ms apart) let the first timer restore time scale in the middle of the second freeze. Let only the newest call restore it, as above.
• 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.