154 lines
6.3 KiB
TypeScript
154 lines
6.3 KiB
TypeScript
/**
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* The railroad, heard.
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*
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* SYNTHESISED, NOT SAMPLED, and that is a constraint rather than a preference. The site is a static
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* folder that fetches nothing — there is a test asserting no page reaches an external host — so an
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* audio file would have to be committed to the repo, and a plausible-sounding whistle is not
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* something to invent. See TODO for sourcing real clips; these stand in until then, which is why
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* sound defaults to off.
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*
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* SELF-CONTAINED ON PURPOSE, like the two board renderers. The playable page imports this; the
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* replay is a single HTML file with an inline script and cannot import anything, so it embeds the
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* function via `Function.toString()`. One implementation either way — a second copy would drift,
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* and a replay that sounds different from the game is worse than a replay with no sound.
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*
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* The AudioContext is parked on `window` rather than in a module variable for the same reason: the
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* embedded copy has no module scope to keep it in, and browsers permit only a handful per page.
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*/
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export function playCue(cue: string): void {
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const w = window as unknown as { __smAudio?: AudioContext; AudioContext?: typeof AudioContext; webkitAudioContext?: typeof AudioContext };
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// "All aboard" is speech, and speech cannot be faked with oscillators. `speechSynthesis` is built
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// into the browser, needs no asset and works offline — but it is whatever system voice the player
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// has, so a real clip is the first thing to replace here.
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if (cue === 'train') {
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try {
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if (window.speechSynthesis && typeof SpeechSynthesisUtterance === 'function') {
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const u = new SpeechSynthesisUtterance('All aboard!');
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u.rate = 0.95;
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u.pitch = 0.85;
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u.volume = 0.9;
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window.speechSynthesis.speak(u);
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return;
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}
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} catch {
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// no voice available — fall through to the two-note call below
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}
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}
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let c: AudioContext;
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try {
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const Ctor = w.AudioContext ?? w.webkitAudioContext;
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if (!Ctor) return;
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// Browsers refuse to start audio until the player has interacted with the page, so the context
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// is made on first use — by which time they have clicked something — and resumed if suspended.
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w.__smAudio ??= new Ctor();
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c = w.__smAudio;
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if (c.state === 'suspended') void c.resume();
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} catch {
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return;
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}
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/** A tone with an envelope, so nothing starts or stops with a click. */
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const tone = (at: number, freq: number, dur: number, gain: number, type: OscillatorType, bendTo?: number): void => {
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const osc = c.createOscillator();
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const amp = c.createGain();
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osc.type = type;
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osc.frequency.setValueAtTime(freq, at);
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if (bendTo !== undefined) osc.frequency.linearRampToValueAtTime(bendTo, at + dur);
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amp.gain.setValueAtTime(0, at);
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amp.gain.linearRampToValueAtTime(gain, at + Math.min(0.04, dur / 4));
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amp.gain.exponentialRampToValueAtTime(0.0001, at + dur);
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osc.connect(amp).connect(c.destination);
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osc.start(at);
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osc.stop(at + dur + 0.02);
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};
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const t = c.currentTime + 0.02;
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if (cue === 'stage') {
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// A real steam whistle is a CHORD of several chambers slightly out of tune with each other,
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// plus the breath of the steam. The beating between the partials IS the sound.
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const d = 1.8;
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for (const fg of [[392, 0.16], [466, 0.13], [587, 0.1], [784, 0.05]]) {
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tone(t, fg[0]!, d, fg[1]!, 'sawtooth', fg[0]! * 0.985);
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}
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const frames = Math.floor(c.sampleRate * d);
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const buf = c.createBuffer(1, Math.max(1, frames), c.sampleRate);
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const data = buf.getChannelData(0);
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for (let i = 0; i < frames; i++) data[i] = Math.random() * 2 - 1;
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const src = c.createBufferSource();
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src.buffer = buf;
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const band = c.createBiquadFilter();
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band.type = 'bandpass';
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band.frequency.value = 1400;
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band.Q.value = 0.8;
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const amp = c.createGain();
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amp.gain.setValueAtTime(0, t);
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amp.gain.linearRampToValueAtTime(0.05, t + 0.05);
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amp.gain.exponentialRampToValueAtTime(0.0001, t + d);
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src.connect(band).connect(amp).connect(c.destination);
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src.start(t);
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src.stop(t + d);
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return;
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}
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if (cue === 'couple') {
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/**
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* KNUCKLE COUPLERS MEETING: a low metallic clank and the slack running out behind it.
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*
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* Coupling a cut was reported as invisible — the car simply left the board and only history said
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* where it went. It is the single most consequential thing a switching move does, so it gets the
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* one sound a player will learn to listen for.
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*/
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for (const fg of [[86, 0.22], [131, 0.13], [197, 0.07], [61, 0.18]]) {
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tone(t, fg[0]!, 0.26, fg[1]!, 'square', fg[0]! * 0.82);
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}
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tone(t + 0.1, 74, 0.34, 0.1, 'triangle', 58);
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return;
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}
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if (cue === 'drop') {
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// Setting out is the same act in reverse and quieter: one clank, no slack behind it.
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for (const fg of [[104, 0.14], [156, 0.08]]) {
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tone(t, fg[0]!, 0.18, fg[1]!, 'square', fg[0]! * 0.85);
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}
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return;
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}
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if (cue === 'schedule') {
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// A die landing on the despatcher's desk, then the slot taking it: a short clatter and a chime.
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for (const at of [t, t + 0.05, t + 0.09]) tone(at, 200 + Math.random() * 90, 0.05, 0.07, 'square');
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tone(t + 0.16, 880, 0.3, 0.09, 'sine');
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tone(t + 0.16, 1320, 0.28, 0.05, 'sine');
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return;
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}
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if (cue === 'completed') {
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// A train clearing the Division and whistling off: two long horn notes falling away, with the
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// second quieter and lower so it reads as distance rather than repetition. Longer than any other
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// cue on purpose — it is the only one that pays every player, and it should land as an event.
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tone(t, 392, 0.55, 0.13, 'sawtooth', 370);
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tone(t, 262, 0.55, 0.09, 'triangle', 247);
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tone(t + 0.42, 330, 0.75, 0.08, 'sawtooth', 300);
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tone(t + 0.42, 220, 0.75, 0.055, 'triangle', 200);
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return;
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}
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if (cue === 'day') {
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// The grade-crossing bell: two strikes. Inharmonic partials separate a bell from a beep.
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for (const at of [t, t + 0.22]) {
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for (const fg of [[1046, 0.13], [1570, 0.09], [2350, 0.06], [3140, 0.03]]) {
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tone(at, fg[0]!, 0.4, fg[1]!, 'square');
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}
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}
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return;
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}
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if (cue === 'train') {
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// Reached only when the platform has no voice: a two-note conductor's call rather than silence.
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tone(t, 523, 0.22, 0.14, 'triangle');
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tone(t + 0.2, 784, 0.34, 0.14, 'triangle');
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}
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}
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