annotate core.js @ 23:c4c7ddaec6fc

Completed Linking for pre-Test questions. Need some formatting on layout.

/**
 * core.js
 * 
 * Main script to run, calls all other core functions and manages loading/store to backend.
 * Also contains all global variables.
 */

/* create the web audio API context and store in audioContext*/
var audioContext;
var projectXML;
var audioEngineContext;
var projectReturn;
var preTestQuestions = document.createElement('PreTest');
var postTestQuestions = document.createElement('PostTest');

window.onload = function() {
	// Function called once the browser has loaded all files.
	// This should perform any initial commands such as structure / loading documents
	
	// Create a web audio API context
	// Fixed for cross-browser support
	var AudioContext = window.AudioContext || window.webkitAudioContext;
	audioContext = new AudioContext;
	
	// Create the audio engine object
	audioEngineContext = new AudioEngine();
};

function loadProjectSpec(url) {
	// Load the project document from the given URL, decode the XML and instruct audioEngine to get audio data
	// If url is null, request client to upload project XML document
	var r = new XMLHttpRequest();
	r.open('GET',url,true);
	r.onload = function() {
		loadProjectSpecCallback(r.response);
	};
	r.send();
};

function loadProjectSpecCallback(response) {
	// Function called after asynchronous download of XML project specification
	var decode = $.parseXML(response);
	projectXML = $(decode);
	
	// Now extract the setup tag
	var xmlSetup = projectXML.find('setup');
	// Detect the interface to use and load the relevant javascripts.
	var interfaceType = xmlSetup[0].attributes['interface'];
	var interfaceJS = document.createElement('script');
	interfaceJS.setAttribute("type","text/javascript");
	if (interfaceType.value == 'APE') {
		interfaceJS.setAttribute("src","ape.js");
	}
	document.getElementsByTagName("head")[0].appendChild(interfaceJS);
}

function createProjectSave(destURL) {
	// Save the data from interface into XML and send to destURL
	// If destURL is null then download XML in client
	// Now time to render file locally
	var xmlDoc = interfaceXMLSave();
	if (destURL == "null" || destURL == undefined) {
		var parent = document.createElement("div");
		parent.appendChild(xmlDoc);
		var file = [parent.innerHTML];
		var bb = new Blob(file,{type : 'application/xml'});
		var dnlk = window.URL.createObjectURL(bb);
		var a = document.createElement("a");
		a.hidden = '';
		a.href = dnlk;
		a.download = "save.xml";
		a.textContent = "Save File";
		
		var submitDiv = document.getElementById('download-point');
		submitDiv.appendChild(a);
	}
}

function AudioEngine() {
	
	// Create two output paths, the main outputGain and fooGain.
	// Output gain is default to 1 and any items for playback route here
	// Foo gain is used for analysis to ensure paths get processed, but are not heard
	// because web audio will optimise and any route which does not go to the destination gets ignored.
	this.outputGain = audioContext.createGain();
	this.fooGain = audioContext.createGain();
	this.fooGain.gain = 0;
	
	// Use this to detect playback state: 0 - stopped, 1 - playing
	this.status = 0;
	
	// Connect both gains to output
	this.outputGain.connect(audioContext.destination);
	this.fooGain.connect(audioContext.destination);
	
	// Create store for new audioObjects
	this.audioObjects = [];
	
	this.play = function() {
		// Send play command to all playback buffers for synchronised start
		// Also start timer callbacks to detect if playback has finished
		if (this.status == 0) {
			// First get current clock
			var timer = audioContext.currentTime;
			// Add 3 seconds
			timer += 3.0;
			
			// Send play to all tracks
			for (var i=0; i<this.audioObjects.length; i++)
			{
				this.audioObjects[i].play(timer);
			}
			this.status = 1;
		}
	};
	
	this.stop = function() {
		// Send stop and reset command to all playback buffers
		if (this.status == 1) {
			for (var i=0; i<this.audioObjects.length; i++)
			{
				this.audioObjects[i].stop();
			}
			this.status = 0;
		}
	};
	
	this.selectedTrack = function(id) {
		for (var i=0; i<this.audioObjects.length; i++)
		{
			if (id == i) {
				this.audioObjects[i].outputGain.gain.value = 1.0;
			} else {
				this.audioObjects[i].outputGain.gain.value = 0.0;
			}
		}
	};
	
	
	this.newTrack = function(url) {
		// Pull data from given URL into new audio buffer
		// URLs must either be from the same source OR be setup to 'Access-Control-Allow-Origin'
		
		// Create the audioObject with ID of the new track length;
		audioObjectId = this.audioObjects.length
		this.audioObjects[audioObjectId] = new audioObject(audioObjectId);

		// AudioObject will get track itself.
		this.audioObjects[audioObjectId].constructTrack(url);
	};
	
}

function audioObject(id) {
	// The main buffer object with common control nodes to the AudioEngine
	
	this.id = id;
	this.state = 0; // 0 - no data, 1 - ready
	
	// Create a buffer and external gain control to allow internal patching of effects and volume leveling.
	this.bufferNode = audioContext.createBufferSource();
	this.outputGain = audioContext.createGain();
	
	// Default output gain to be zero
	this.outputGain.gain.value = 0.0;
	
	// Connect buffer to the audio graph
	this.bufferNode.connect(this.outputGain);
	this.outputGain.connect(audioEngineContext.outputGain);
	
	// the audiobuffer is not designed for multi-start playback
	// When stopeed, the buffer node is deleted and recreated with the stored buffer.
	this.buffer;
	
	this.play = function(startTime) {
		this.bufferNode.start(startTime);
	};
	
	this.stop = function() {
		this.bufferNode.stop(0);
		this.bufferNode = audioContext.createBufferSource();
		this.bufferNode.connect(this.outputGain);
		this.bufferNode.buffer = this.buffer;
		this.bufferNode.loop = true;
	};

	this.constructTrack = function(url) {
		var request = new XMLHttpRequest();
		request.open('GET',url,true);
		request.responseType = 'arraybuffer';
		
		var audioObj = this;
		
		// Create callback to decode the data asynchronously
		request.onloadend = function() {
			audioContext.decodeAudioData(request.response, function(decodedData) {
				audioObj.buffer = decodedData;
				audioObj.bufferNode.buffer = audioObj.buffer;
				audioObj.bufferNode.loop = true;
				audioObj.state = 1;
			}, function(){
				// Should only be called if there was an error, but sometimes gets called continuously
				// Check here if the error is genuine
				if (audioObj.state == 0 || audioObj.buffer == undefined) {
					// Genuine error
					console.log('FATAL - Error loading buffer on '+audioObj.id);
				}
			});
		};
		request.send();
	};
	
}