---

name: input-systems
description: >
Architect game input — action mapping (abstracting keys into named actions),
rebinding with conflict detection and persistence, multi-device support
(keyboard, gamepad, touch), analog deadzones, and feel features like input
buffering and coyote time, plus accessibility. Engine-neutral. Use when the
user mentions input mapping, rebind controls, gamepad support, deadzone, input
buffering, coyote time, or accessible controls.

Input systems

Never wire gameplay to raw keys. Map physical inputs (a key, a button, a touch)
to named actions (jump, interact, move), and let gameplay read actions.
That one indirection gives you rebinding, multi-device support, and accessibility
almost for free. This skill is the engine-neutral architecture; bind it to
unity-input-system, unreal-enhanced-input, or Godot's InputMap.

When to use

• Use to design an input layer: actions, bindings, multiple devices, and a
  rebinding UI with conflict detection and saved bindings.
• Use to add analog handling (deadzones, sensitivity) and game-feel features
  (input buffering, coyote time).
• Use to make controls accessible (full remapping, hold-vs-toggle, sensitivity,
  no required simultaneous presses).

When not to use: for an engine's concrete input package/API, use
unity-input-system, unreal-enhanced-input, or Godot's InputMap. For the
movement/jump physics the buffer feeds, see physics-tuning and the engine
movement skill. Persisting bindings to disk is save-systems.

Core workflow

1. Define actions, not keys. Gameplay asks "is jump pressed?", never "is
   Space pressed?". Actions are the stable contract; bindings are data.
2. Bind per device. Each action holds bindings for keyboard, gamepad, and
   touch. The active device is whichever last sent input; swap UI prompts to match.
3. Read the right edge. Use pressed-this-frame (edge) for discrete actions
   (jump, interact) and held (level) for continuous ones (move, aim). Confusing
   the two causes double-fires or missed presses.
4. Filter analog input. Apply a deadzone to sticks/triggers so resting drift
   reads as zero, and scale sensitivity/curve to taste.
5. Buffer for feel. Remember a pressed action for a short window so a slightly
   early press still fires (input buffering); allow a jump shortly after leaving a
   ledge (coyote time).
6. Make rebinding first-class. A UI that captures the next input, detects
   conflicts, and persists bindings — and a reset-to-default. Save via
   save-systems.
7. Verify on every device and with rebinds: keyboard, gamepad, touch; rebind
   an action mid-game and confirm gameplay and prompts follow.

Patterns

1. Actions over raw keys; edge vs held

# Gameplay reads ACTIONS. The mapping from key/button to action lives in data.
# Discrete (edge): fire once on the press frame.
if Input.is_action_just_pressed("jump"):
    try_jump()
# Continuous (held): read every frame as an axis.
var move := Input.get_axis("move_left", "move_right")   # -1..1
player.velocity.x = move * RUN_SPEED
# RIGHT: name actions ("jump"); rebinding/devices just change the binding data.
# WRONG: `if Input.is_key_pressed(KEY_SPACE)` — unrebindable, keyboard-only,
# and `is_key_pressed` is a held check that would re-fire jump every frame.

Engine equivalents: Godot InputMap + Input.is_action_just_pressed; Unity
Input System InputAction / action maps; Unreal Enhanced Input Input Actions +
Input Mapping Contexts.

2. Analog deadzone and sensitivity

# Raw sticks never rest at exactly zero. Apply a RADIAL deadzone (on the vector
# length), not per-axis, so diagonals aren't clipped into the axes.
func apply_deadzone(stick: Vector2, dead := 0.2, sens := 1.0) -> Vector2:
    var mag := stick.length()
    if mag < dead:
        return Vector2.ZERO                      # inside deadzone -> no movement
    # Rescale so motion ramps from 0 at the edge of the deadzone, not from `dead`.
    var scaled := (mag - dead) / (1.0 - dead)
    return stick.normalized() * pow(scaled, sens)  # sens>1 = finer near center
# WRONG: clamping each axis separately — it carves a square hole and snaps to axes.

3. Input buffering + coyote time (forgiving, responsive feel)

# Buffer: a jump pressed slightly BEFORE landing still triggers on touchdown.
# Coyote: a jump pressed slightly AFTER walking off a ledge still works.
const BUFFER := 0.12   # seconds an early press stays "remembered"
const COYOTE := 0.10   # seconds after leaving ground you can still jump
var _buffer_timer := 0.0
var _coyote_timer := 0.0

func _physics_process(dt):
    _buffer_timer -= dt
    _coyote_timer = COYOTE if is_on_floor() else _coyote_timer - dt
    if Input.is_action_just_pressed("jump"):
        _buffer_timer = BUFFER                  # remember the press
    if _buffer_timer > 0.0 and _coyote_timer > 0.0:
        velocity.y = JUMP_VELOCITY
        _buffer_timer = 0.0; _coyote_timer = 0.0  # consume both so it fires once

4. Rebinding with conflict detection

# Capture the next physical input, reject duplicates, then persist.
func rebind(action: String, event: InputEvent) -> bool:
    for other in actions:                        # conflict check across actions
        if other != action and binding_of(other) == event:
            return false                         # already used -> let UI warn/swap
    set_binding(action, event)                   # engine: erase old + add new event
    save_bindings()                              # persist (see save-systems)
    return true
# Always provide "reset to defaults", and never let the player unbind a key they
# need to reach the menu without an alternative.

Pitfalls

• Hardcoding keys in gameplay blocks rebinding, locks out gamepad/touch, and
  scatters input logic. Read named actions only.
• Edge vs held confusion: using a held check for jump re-fires every frame;
  using an edge check for movement drops held input. Match the check to the action.
• Per-axis deadzones clip diagonal stick input and snap movement to the axes.
  Use a radial deadzone on the vector magnitude.
• No buffering/coyote time makes tight platformers feel unfair even when the
  physics are correct — players "clearly pressed jump". Add small windows.
• Rebinding without conflict handling lets two actions share a key, or strands
  the player by unbinding menu access. Detect conflicts; guarantee a way back.
• Not swapping prompts on device change shows "Press Space" to a gamepad
  player. Track the last-used device and switch glyphs.
• Ignoring accessibility: required simultaneous presses, no remap, fixed
  sensitivity, hold-only actions. Offer remap, toggle-vs-hold, and sensitivity.
• Reading input in the wrong loop: poll held state in the physics step for
  consistent movement; capture discrete presses so none are missed between frames.

References

• references/buffering-and-accessibility.md — buffering/coyote tuning, jump feel
  (variable height, apex), device detection and prompt swapping, touch controls,
  and an accessibility checklist (remap, toggle/hold, sensitivity, latency).

Related skills

• unity-input-system, unreal-enhanced-input — concrete engine input APIs
  (Godot uses InputMap + the Input singleton).
• save-systems — persist custom key bindings and input settings.
• physics-tuning — the movement the buffer/coyote windows feed into.
• platformer, fps-shooter — genres whose feel depends on input handling.