music21j-port/src/ext/midijs/inc/jasmid/replayer.js

A toolkit for computer-aided musicology, Javascript version

/**
 * Replayer class -- factored from function by MSC July 2019
 *
 */


/**
 * Clone any object
 *
 * @param {*} o
 * @returns {Array|*}
 */
const clone = o => {
	if (typeof o != 'object') {
		return o;
	}
	if (o == null) {
		return o;
	}
	const ret = (typeof o.length == 'number') ? [] : {};
	for (let key in o) {
		// noinspection JSUnfilteredForInLoop
		ret[key] = clone(o[key]);
	}
	return ret;
};

export class Replayer {
	constructor(midiFile, timeWarp, eventProcessor, bpm) {
		this.midiFile = midiFile;
		this.timeWarp = timeWarp;
		this.eventProcessor = eventProcessor;
		this.trackStates = [];
		this.beatsPerMinute = bpm ? bpm : 120;
		this.bpmOverride = !!bpm;
		this.ticksPerBeat = midiFile.header.ticksPerBeat;

		for (let i = 0; i < midiFile.tracks.length; i++) {
			this.trackStates[i] = {
				'nextEventIndex': 0,
				'ticksToNextEvent': (
					midiFile.tracks[i].length ?
						midiFile.tracks[i][0].deltaTime :
						null
				)
			};
		}
		this.temporal = [];
		this.processEvents();
	}

	getNextEvent() {
		let ticksToNextEvent = null;
		let nextEventTrack = null;
		let nextEventIndex = null;
		
		for (let i = 0; i < this.trackStates.length; i++) {
			if (
				this.trackStates[i].ticksToNextEvent != null
				&& (ticksToNextEvent == null || this.trackStates[i].ticksToNextEvent < ticksToNextEvent)
			) {
				ticksToNextEvent = this.trackStates[i].ticksToNextEvent;
				nextEventTrack = i;
				nextEventIndex = this.trackStates[i].nextEventIndex;
			}
		}
		if (nextEventTrack != null) {
			/* consume event from that track */
			const nextEvent = this.midiFile.tracks[nextEventTrack][nextEventIndex];
			if (this.midiFile.tracks[nextEventTrack][nextEventIndex + 1]) {
				this.trackStates[nextEventTrack].ticksToNextEvent += this.midiFile.tracks[nextEventTrack][nextEventIndex + 1].deltaTime;
			} else {
				this.trackStates[nextEventTrack].ticksToNextEvent = null;
			}
			this.trackStates[nextEventTrack].nextEventIndex += 1;
			/* advance timings on all tracks by ticksToNextEvent */
			for (let i = 0; i < this.trackStates.length; i++) {
				if (this.trackStates[i].ticksToNextEvent != null) {
					this.trackStates[i].ticksToNextEvent -= ticksToNextEvent
				}
			}
			return {
				"ticksToEvent": ticksToNextEvent,
				"event": nextEvent,
				"track": nextEventTrack
			}
		} else {
			return null;
		}
	}

	processEvents() {
		let midiEvent = this.getNextEvent();
		while(midiEvent) {
		    if (!this.bpmOverride && midiEvent.event.type === "meta" && midiEvent.event.subtype === "setTempo" ) {
				// tempo change events can occur anywhere in the middle and affect events that follow
				this.beatsPerMinute = 60000000 / midiEvent.event.microsecondsPerBeat;
			}
			//
			let beatsToGenerate = 0;
			let secondsToGenerate = 0;
			if (midiEvent.ticksToEvent > 0) {
				beatsToGenerate = midiEvent.ticksToEvent / this.ticksPerBeat;
				secondsToGenerate = beatsToGenerate / (this.beatsPerMinute / 60);
			}

			const time = (secondsToGenerate * 1000 * this.timeWarp) || 0;
			this.temporal.push([midiEvent, time]);
			midiEvent = this.getNextEvent();
		}
	}

	getData() {
		return clone(this.temporal);
	}
}