Controls (player-visible signs — do not ship inverted)

Read this end-to-end before writing movement/steer/flight code for any game that uses WASD, arrows, a chase camera, or a flying craft. Do not skip this and only open racing-kart or fps — those genre files assume you already know these signs. Inverted A/D is the most common ship-blocker in vehicle and flight demos.

Pair with building-games (loop, camera, 3D orientation) and building-games/references/input.md (keydown state, gamepad, touch). This skill owns what left/right/up mean to the player and how you prove it.

0. Hard rules (fail the build if broken)

1. Player-visible left/right is law. From a chase / behind camera while the craft moves forward:
   • A / ← → nose (or bank) turns left on screen
   • D / → → nose (or bank) turns right on screen
2. Never reuse FPS strafe as vehicle steer. FPS “D → +right vector” is position on the ground plane. Vehicle A/D is yaw (or roll) rate, not a strafe offset. Mixing them is the #1 cause of inverted A/D.
3. You must run a control self-test (§5) before saying done. Screenshot-only QA is not enough. If A turns right, flip the steer/roll sign, retest, then ship — do not invent a new coordinate story.

1. Shared 3D basis (use this everywhere)

three.js: right-handed, +Y up, meshes face +Z, cameras look −Z.

Yaw-only heading on XZ (ground vehicles, walkers, most arcade craft):

// yaw = 0 faces world −Z; +yaw is CCW about +Y (nose moves toward −X)
forward = (-sin(yaw), 0, -cos(yaw))
right   = ( cos(yaw), 0, -sin(yaw))   // = normalize(cross(forward, worldUp))

With a chase cam behind the craft (camera near position - forward * dist):

If your basis differs, keep one consistent pair — but the player-visible row above is mandatory.

2. Genre maps

2a. FPS / on-foot (strafe, not steer)

W = +forward, S = −forward, D = +right, A = −right   // position, not yaw
mouse: yaw -= movementX * sens; pitch -= movementY * sens; clamp pitch

Body yaw for look; movement uses yaw only (do not apply pitch to walk).

2b. Ground / water vehicle (kart, bike, jetski, boat, tank, rover, snowmobile)

Arcade body with heading/yaw and forward speed:

// Input (held keys → actions once per frame)
let steer = 0; // -1..+1, player-visible
if (keys.has('KeyA') || keys.has('ArrowLeft'))  steer += 1;  // LEFT
if (keys.has('KeyD') || keys.has('ArrowRight')) steer -= 1;  // RIGHT
// Optional: steer = clamp(steer + gamepadX, -1, 1) with same sign convention

// Integrate (speedFactor ~ 0..1 from |speed|)
const reverse = speed >= 0 ? 1 : -1; // wheel-left still feels left in reverse
yaw += steer * turnRate * speedFactor * reverse * dt;

// Move along heading
const fx = -Math.sin(yaw), fz = -Math.cos(yaw);
position.x += fx * speed * dt;
position.z += fz * speed * dt;

Canonical bug (do not copy):

// WRONG — this is what ships inverted A/D in the wild
if (KeyA) steer -= 1;
if (KeyD) steer += 1;
yaw += steer * turnRate * dt;  // A → −yaw → nose RIGHT on chase cam

If you already wrote KeyA → steer--, either swap the key mapping or negate once at integrate (yaw += -steer * …) — then run §5. Do not flip twice (keys + integrate + bank mesh).

2c. Fixed-wing flight (airplane, glider, RC plane)

• A/D are not strafe and not “ground steer with FPS signs.”
• Apply roll in the craft’s local forward axis with a sign that matches bank left on A. If the mesh banks the wrong way, flip one sign on the roll apply (or on the A/D → roll mapping), not the whole basis.
• Coordinated turn: positive bank should produce a turn that matches the bank direction under the chase/external cam.

2d. Heli / drone / 6DOF

Document the scheme on a start overlay. Minimum:

• Throttle/altitude on discrete keys must not stick “always up” after one press (use held state or explicit up/down).
• Strafe/yaw: A left, D right in the craft’s horizontal frame (player-visible).

2e. 2D side-scroller / platformer

D / → moves right on screen; A / ← moves left. Gravity only inverted if the genre is explicitly upside-down.

3. Camera must agree

• Chase cam: desired = craftPos + up*height + forward*(-followDist); lerp; lookAt(craft).
• Compute forward once for both movement and camera — do not rebuild with opposite yaw sign in the camera path.
• Debug order: (1) keys register → (2) signs correct (§5) → (3) camera agrees.

4. Input plumbing (brief)

• Track keys with a Set on keydown/keyup using event.code; clear on blur / visibilitychange. Move in the game loop with dt, not in the key handler.
• Unify keyboard + touch + gamepad into actions (throttle, steer, pitch, roll, …). See building-games/references/input.md.
• Touch: left stick = move/steer, right = actions; ≥44px targets.

5. Mandatory control self-test (before “done”)

Screenshot-only is not enough for any craft with A/D.

5a. Player-visible checklist (every vehicle / flight build)

While moving forward (speed > small epsilon), chase cam behind:

If A fails: flip steer/roll sign once, retest both A and D.

5b. Minimal test interface (implement this)

Expose a tiny hook so you (and automated QA) can prove signs without guessing private closures:

// e.g. src/game/controlsTest.ts — dev/QA only is fine
export type ControlsProbe = {
  getYaw: () => number;       // radians; or getHeading()
  getSpeed: () => number;
  /** Inject held actions for one frame path; clear after test */
  setSteer?: (v: number) => void; // -1..1, same sign as production
  setKeys?: (codes: string[]) => void;
};

declare global {
  interface Window {
    __controlsTest?: ControlsProbe;
  }
}

Wire window.__controlsTest from the game loop when import.meta.env.DEV or a ?qa=1 flag is set.

5c. Automated smoke (run it)

In a short Playwright / agent script against the local preview:

1. Start / click-to-play so the sim runs.
2. Set forward throttle; wait until getSpeed() > threshold.
3. Record y0 = getYaw().
4. Hold A (or setSteer(+1) if that is your left convention) for 500ms.
5. Assert deltaAngle(getYaw(), y0) has the left sign for your basis (with the §1 basis: left ⇒ yaw increased).
6. Repeat for D with opposite sign.
7. Fail the build if either assert fails; fix signs; re-run.

Pseudo-assert for the §1 basis:

const wrap = (a) => Math.atan2(Math.sin(a), Math.cos(a));
// After holding A (left) while moving forward:
expect(wrap(yawAfter - yawBefore)).toBeGreaterThan(0.05);
// After holding D:
expect(wrap(yawAfter - yawBefore)).toBeLessThan(-0.05);

For planes, assert roll (or on-screen bank) the same way: A ⇒ bank left.

5d. What not to do

• Do not only test “D increases some internal variable.”
• Do not use FPS “D → +X when facing −Z” as the vehicle pass condition.
• Do not flip mesh bank, camera, and steer all at once when fixing — change one sign, retest.

6. Finish criteria (controls)

• Opened this skill before writing movement/steer/flight.
• Genre map chosen (§2) and start-screen / HUD labels match it.
• Chase-cam A/D player-visible test passed (§5a).
• window.__controlsTest (or equivalent) available in dev/QA and used once.
• No inverted bank mesh relative to roll/steer input.
• Keys are held-state + dt-scaled; no sticky thrust from a single Space tap unless intentional and labeled.

If any box is unchecked, the game is not done.