references/buffering-and-accessibility.md
# Input buffering, game feel, devices, and accessibility
The action layer makes controls work; these refinements make them feel good and
reach more players.
## Buffering and coyote time, tuned
Both convert "I pressed it at almost the right moment" into success:
- **Input buffer** — when an action is pressed but can't fire yet (mid-air jump,
attack during recovery), remember it for a short window and fire the instant it
becomes valid. Typical window: ~100–150 ms (≈6–9 frames at 60 Hz).
- **Coyote time** — allow a ground action (jump) for a brief window *after*
leaving the ledge. Typical window: ~80–120 ms. Players perceive the edge as
generous, not buggy.
Tuning notes:
- Express windows in **seconds**, not frames, so they're frame-rate independent.
- **Consume** the buffer when it fires, and reset coyote on a successful jump, so
one press = one action (no double jumps from a lingering buffer).
- Too-long windows feel mushy or cause unintended actions; too-short feel
punishing. Tune by playtest, per game.
## Jump feel (where input meets physics)
Input handling and `physics-tuning` together create jump feel:
- **Variable height**: full gravity while rising only if the button is held; if
released early, increase downward acceleration (or cut upward velocity) so a tap
is a short hop. Read the *held* state for this, the *edge* for the initial jump.
- **Apex hang**: reduce gravity near the top of the arc for a brief float — gives
air control and reads as responsive.
- **Fast fall / increased fall gravity**: heavier gravity on the way down than up
makes jumps feel snappy rather than floaty.
These are physics tweaks driven by input state; keep the input layer reporting
edge/held cleanly so the controller can apply them.
## Device detection and prompt swapping
- Track the **last-used device**: when an event arrives, note whether it was
keyboard/mouse, a specific gamepad type, or touch. Switch on-screen button
glyphs and tutorials to match.
- Don't assume a single gamepad layout — Xbox, PlayStation, and Switch differ in
face-button labels. Map to abstract **positions** (South/East/West/North) and
pick the icon set per controller. SDL3 names buttons this way
(`SDL_GAMEPAD_BUTTON_SOUTH`…, with `SDL_GetGamepadButtonLabel` and
`SDL_GetGamepadType` for the printed label and family), and so does Godot 4.7,
whose desktop joypad driver is SDL3: `JOY_BUTTON_A` is the bottom button —
Xbox A, PlayStation Cross, Nintendo B. Read the family from
`Input.get_joy_name()` / `Input.get_joy_info()` (vendor and product IDs).
- **Steam Input** may sit between the pad and your game: when it is on for a
controller, the game sees an emulated Xbox-style pad, so name and ID checks
report Xbox even for a PlayStation or Switch pad and you show the wrong
glyphs. Ask Steam for the real type (`ISteamInput::GetControllerForGamepadIndex`
+ `GetInputTypeForHandle`; Godot exposes the index as `steam_input_index` in
`get_joy_info()`), or fetch Steam's own art (`GetGlyphPNGForActionOrigin` /
`GetGlyphSVGForActionOrigin`).
- Godot 4.7's SDL3 joypad driver covers Windows, Linux and macOS; on Android and
Web `get_joy_info()` is empty, so fall back to `get_joy_name()` there.
- Support **hot-swapping**: a player may start on keyboard and pick up a
controller mid-session. Re-resolve prompts on device change without a restart.
## Touch controls
- Provide on-screen controls sized for thumbs (virtual stick / buttons) or
gesture mappings, routed through the **same action layer** as physical input.
- A virtual stick should use a **floating origin** (anchor where the thumb lands)
and a radial deadzone, just like a physical stick.
- Avoid relying on precise multi-touch chords; offer larger hit areas and
forgiving timing. Test on a range of screen sizes.
## Accessibility checklist
Input is one of the highest-impact accessibility surfaces. Aim for:
- **Full remapping** of every action, for every device, with conflict detection
and reset-to-default.
- **Toggle vs hold** options for actions that default to hold (aim, crouch,
sprint) — sustained presses are painful or impossible for some players.
- **No required simultaneous inputs** for essential actions; offer single-input
alternatives or sequential equivalents.
- **Adjustable sensitivity and deadzone** for sticks and aim, plus optional
aim assist.
- **Adjustable timing windows** where feasible (extend buffer/coyote, slow QTEs),
or a "hold instead of mash" option for repeated-press prompts.
- **Stick/axis inversion** (X and Y independently) for camera and movement.
- **Input latency**: process discrete presses promptly and avoid adding
artificial delay; perceived lag harms both feel and accessibility.
## Loop placement
- Read **held/axis** state in the fixed/physics step so movement is consistent
with the simulation (see `physics-tuning`).
- Capture **discrete presses** as events (or via a just-pressed flag latched each
frame) so a press between physics ticks is never lost.
- Save custom bindings and input settings through `save-systems` and reload them
at startup before the first frame of gameplay.
SKILL.md
---
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
```gdscript
# 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, one axis
player.velocity.x = move * RUN_SPEED
# Two axes (stick or WASD): get_vector applies a circular deadzone, rescales
# past it and caps the length at 1, so diagonals are not faster.
var dir := Input.get_vector("move_left", "move_right", "move_up", "move_down")
# 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 4.7, Unity 6.3 LTS, Unreal 5.8): Godot `InputMap` +
`Input.is_action_just_pressed` (valid in `_process` and `_physics_process`);
Unity Input System `InputAction` / action maps; Unreal Enhanced Input `Input
Actions` + `Input Mapping Contexts`.
### 2. Analog deadzone and sensitivity
```gdscript
# 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, curve := 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 := minf((mag - dead) / (1.0 - dead), 1.0) # some pads report > 1 on diagonals
return stick / mag * pow(scaled, curve) # curve > 1 = finer aim near center
# WRONG: clamping each axis separately — it carves a square hole and snaps to axes.
```
Keep the response curve (exponent) separate from sensitivity (a plain gain on
the result, usually a camera turn rate) and expose both. Godot's `get_vector`
already does the deadzone and rescale above, using the average of the four
actions' deadzones (0.2 by default per action) unless you pass one.
### 3. Input buffering + coyote time (forgiving, responsive feel)
```gdscript
# 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
```gdscript
# Godot 4.7. Capture the next physical input, reject conflicts, then persist.
var _waiting_for: StringName = &"" # set by the "press a key for Jump" button
func _unhandled_input(event: InputEvent) -> void:
if _waiting_for != &"" and _is_bindable(event):
get_viewport().set_input_as_handled()
if not rebind(_waiting_for, event):
show_conflict_warning(event) # offer swap or cancel
_waiting_for = &""
func _is_bindable(e: InputEvent) -> bool:
if e is InputEventKey or e is InputEventJoypadButton or e is InputEventMouseButton:
return e.pressed and not e.is_echo() # ignore releases and key repeat
return e is InputEventJoypadMotion and absf(e.axis_value) > 0.5 # ignore stick noise
func rebind(action: StringName, captured: InputEvent) -> bool:
var event := _to_binding(captured)
for other in InputMap.get_actions():
if other != action and not String(other).begins_with("ui_") \
and InputMap.action_has_event(other, event):
return false # already used -> let UI warn/swap
for old in InputMap.action_get_events(action):
if old.get_class() == event.get_class(): # replace only this device kind's binding
InputMap.action_erase_event(action, old)
InputMap.action_add_event(action, event)
save_bindings() # persist (see save-systems)
return true
func _to_binding(e: InputEvent) -> InputEvent:
if e is InputEventKey: # bind the physical key, not the layout's letter
var k := InputEventKey.new()
k.physical_keycode = e.physical_keycode
return k
var b := e.duplicate() as InputEvent
b.device = -1 # all devices: a pad binding must not stick to pad 0
if b is InputEventJoypadMotion:
b.axis_value = signf(b.axis_value) # keep the direction only
return b
# Compare bindings with action_has_event() / InputEvent.is_match(), never `==`:
# two InputEvents with the same key are different objects, so `==` is false.
# Always provide "reset to defaults" (InputMap.load_from_project_settings()), and
# never let the player unbind a key they need to reach the menu without an alternative.
```
Keyboard bindings use the **physical** key (`physical_keycode`, with `keycode`
left at 0, which is what makes Godot match by position), so WASD stays in the
same place on AZERTY or Dvorak; show the label for the player's layout with
`DisplayServer.keyboard_get_label_from_physical`. Unity Input System `action.PerformInteractiveRebinding()` and
`SaveBindingOverridesAsJson()` / `LoadBindingOverridesFromJson()`; Unreal
Enhanced Input **User Settings** (enable under Project Settings ▸ Enhanced Input)
with player-mappable keys on the mapping context.
## 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.
- **WASD lands in the wrong place on AZERTY/QWERTZ**: bindings stored by key
*letter* follow the layout. Store physical key positions and display the
layout's label.
- **A rebound gamepad button works only for player 1**: the captured event
carried pad 0's device ID. Store bindings for all devices (Godot `device = -1`)
unless the game assigns pads to players on purpose.
- **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.