input-systems

SKILL.md

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

Define actions, not keys. Gameplay asks "is jump pressed?", never "is
Space pressed?". Actions are the stable contract; bindings are data.

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.

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.

Filter analog input. Apply a deadzone to sticks/triggers so resting drift
reads as zero, and scale sensitivity/curve to taste.

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).

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.

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.