Tone.js/Tone/instrument/Instrument.ts

import { Volume } from "../component/channel/Volume";
import { Param } from "../core/context/Param";
import { OutputNode, ToneAudioNode, ToneAudioNodeOptions } from "../core/context/ToneAudioNode";
import { Decibels, Frequency, NormalRange, Time } from "../core/type/Units";
import { optionsFromArguments } from "../core/util/Defaults";
import { readOnly } from "../core/util/Interface";

export interface InstrumentOptions extends ToneAudioNodeOptions {
	volume: Decibels;
}

/**
 *  Base-class for all instruments
 */
export abstract class Instrument<Options extends InstrumentOptions> extends ToneAudioNode<Options> {

	/**
	 *  The output and volume triming node
	 */
	private _volume: Volume;
	output: OutputNode;

	/**
	 * The instrument only has an output
	 */
	input: undefined;

	/**
	 * The volume of the output in decibels.
	 * @example
	 * source.volume.value = -6;
	 */
	volume: Param<Decibels>;

	/**
	 * Keep track of all events scheduled to the transport
	 * when the instrument is 'synced'
	 */
	private _scheduledEvents: number[] = [];

	/**
	 * If the instrument is currently synced
	 */
	private _synced: boolean = false;

	constructor(options?: Partial<InstrumentOptions>);
	constructor() {

		super(optionsFromArguments(Instrument.getDefaults(), arguments));
		const options = optionsFromArguments(Instrument.getDefaults(), arguments);

		this._volume = new Volume({
			context: this.context,
			volume: options.volume,
		});
		this.volume = this._volume.volume;
		this.output = this._volume;
		readOnly(this, "volume");
	}

	static getDefaults(): InstrumentOptions {
		return Object.assign(ToneAudioNode.getDefaults(), {
			volume: 0,
		});
	}

	/**
	 * Sync the instrument to the Transport. All subsequent calls of
	 * [triggerAttack](#triggerattack) and [triggerRelease](#triggerrelease)
	 * will be scheduled along the transport.
	 * @example
	 * instrument.sync()
	 * //schedule 3 notes when the transport first starts
	 * instrument.triggerAttackRelease('C4', '8n', 0)
	 * instrument.triggerAttackRelease('E4', '8n', '8n')
	 * instrument.triggerAttackRelease('G4', '8n', '4n')
	 * //start the transport to hear the notes
	 * Transport.start()
	 * @returns {Instrument} this
	 */
	sync(): this {
		if (!this._synced) {
			this._synced = true;
			this._syncMethod("triggerAttack", 1);
			this._syncMethod("triggerRelease", 0);
		}
		return this;
	}

	/**
	 * Wrap the given method so that it can be synchronized
	 * @param method Which method to wrap and sync
	 * @param  timePosition What position the time argument appears in
	 */
	protected _syncMethod(method: string, timePosition: number): void {
		const originalMethod = this["_original_" + method] = this[method];
		this[method] = (...args: any[]) => {
			const time = args[timePosition];
			const id = this.context.transport.schedule((t) => {
				args[timePosition] = t;
				originalMethod.apply(this, args);
			}, time);
			this._scheduledEvents.push(id);
		};
	}

	/**
	 * Unsync the instrument from the Transport
	 */
	unsync(): this {
		this._scheduledEvents.forEach(id => this.context.transport.clear(id));
		this._scheduledEvents = [];
		if (this._synced) {
			this._synced = false;
			this.triggerAttack = this._original_triggerAttack;
			this.triggerRelease = this._original_triggerRelease;
		}
		return this;
	}

	/**
	 *  Trigger the attack and then the release after the duration.
	 *  @param  note     The note to trigger.
	 *  @param  duration How long the note should be held for before
	 *                          triggering the release. This value must be greater than 0.
	 *  @param time  When the note should be triggered.
	 *  @param  velocity The velocity the note should be triggered at.
	 *  @example
	 * //trigger "C4" for the duration of an 8th note
	 * synth.triggerAttackRelease("C4", "8n");
	 */
	triggerAttackRelease(note: Frequency, duration: Time, time?: Time, velocity?: NormalRange): this {
		const computedTime = this.toSeconds(time);
		const computedDuration = this.toSeconds(duration);
		this.triggerAttack(note, computedTime, velocity);
		this.triggerRelease(computedTime + computedDuration);
		return this;
	}

	/**
	 * Start the instrument's note.
	 * @param note the note to trigger
	 * @param time the time to trigger the ntoe
	 * @param velocity the velocity to trigger the note (betwee 0-1)
	 */
	abstract triggerAttack(note: Frequency, time?: Time, velocity?: NormalRange): this;
	// tslint:disable-next-line: variable-name
	private _original_triggerAttack = this.triggerAttack;

	/**
	 * Trigger the release phase of the current note.
	 *  @param time when to trigger the release
	 */
	abstract triggerRelease(...args: any[]): this;
	// tslint:disable-next-line: variable-name
	private _original_triggerRelease = this.triggerRelease;

	/**
	 *  clean up
	 *  @returns {Instrument} this
	 */
	dispose(): this {
		super.dispose();
		this._volume.dispose();
		this.unsync();
		this._scheduledEvents = [];
		return this;
	}
}