protracker.js

function proTracker() {};
proTracker.prototype.proTrackerInstStruct = [
  "name", "string:22", 
  "sampleLength", "uint16be",
  "finetune", "uint8",
  "volume", "uint8",
  "repeatStart", "uint16be",
  "repeatSize", "uint16be"
];

proTracker.prototype.proTrackerSongStruct = [
  "numPositions", "uint8",
  "oneHundredAndTwentySeven", "uint8",
  "songTable", ["[]", "uint8", 128]
];

proTracker.prototype.proTrackerSongStruct32 = [
  "numPositions", "uint8",
  "oneHundredAndTwentySeven", "uint8",
  "songTable", ["[]", "uint8", 128],
  "chString", "string:4"
];

proTracker.prototype.inst = [];
proTracker.prototype.song = [];
proTracker.prototype.patterns = [];
proTracker.prototype.samples = [];
proTracker.prototype.WAsamples = [];
proTracker.prototype.numPatterns = 0;
proTracker.prototype.numSamples = 15; //15 by default

proTracker.prototype.parsePattern = function(arrayBuffer) {
  var pattern = [];
  var bv = new BitView(arrayBuffer);
  pattern["sample"] = //I am not proud of this
    (bv.getBit(0) << 7) +
    (bv.getBit(1) << 6) +
    (bv.getBit(2) << 5) +
    (bv.getBit(3) << 4) +
    (bv.getBit(16) << 3) +
    (bv.getBit(17) << 2) +
    (bv.getBit(18) << 1) +
    bv.getBit(19);

  pattern["param"] = bv.getInt12(4) + 2048; //Unsigned 12-bit int
  pattern["effect"] = bv.getInt12(20) + 2048; //Unsigned 12-bit int
  return pattern;
}


//Parse ProTracker Modules
proTracker.prototype.parseFile = function(arrayBuffer, parent) {
  //Create DataStream and get the modfile's name
  var ds = new DataStream(arrayBuffer, 0, DataStream.BIG_ENDIAN); //all Protracker mods are Big Endian.
  parent.modName = new TextDecoder("utf-8").decode(ds.readUint8Array(20));
  
  //Check for a 15 or 31 sample modfile
  var curPos = ds.position;
  ds.seek(950);
  var tempStruct = ds.readStruct(this.proTrackerSongStruct32);
  if(tempStruct.chString != "" && tempStruct.oneHundredAndTwentySeven == 127) { //check both formatting indicators
    this.numSamples = 31;
  }
  ds.seek(curPos);

  //Read instrument and song data
  for(i=0; i < this.numSamples; i++) {
    this.inst[i] = ds.readStruct(this.proTrackerInstStruct);
  }
  if(this.numSamples == 31) {
    this.song = ds.readStruct(this.proTrackerSongStruct32);
  }
  else {
    this.song = ds.readStruct(this.proTrackerSongStruct);
  }
  console.log("Successfully found pattern data start at 0x" + ds.position.toString(16));
  //get total number of patterns
  for(i=0; i < 128; i++) {
    if(this.song.songTable[i] > this.numPatterns) {
      this.numPatterns = this.song.songTable[i];
    }
  }
  
  //read in pattern data
  for(i=0; i <= this.numPatterns; i++) {
    this.patterns[i] = [];
    this.patterns[i][0] = [];
    this.patterns[i][1] = [];
    this.patterns[i][2] = [];
    this.patterns[i][3] = [];
    for(j=0; j < 64; j++) { //64 entries per pattern
      this.patterns[i][0][j] = this.parsePattern(ds.readUint8Array(4).buffer);
      this.patterns[i][1][j] = this.parsePattern(ds.readUint8Array(4).buffer);
      this.patterns[i][2][j] = this.parsePattern(ds.readUint8Array(4).buffer);
      this.patterns[i][3][j] = this.parsePattern(ds.readUint8Array(4).buffer);
    }
  }

  //spit out debug info
  console.log("Successfully parsed " + this.numPatterns + " patterns with " + this.numSamples + " samples");

  //read in sample data
  for(i=0; i < this.numSamples; i++) {
    console.log("Reading sample from 0x" + ds.position.toString(16) + " with length of " + (this.inst[i].sampleLength*2).toString() + " bytes and repeat length of " + (this.inst[i].repeatSize*2).toString());
    this.samples[i] = ds.readInt8Array(this.inst[i].sampleLength*2);
  }
  
  //normalise sample data to WebAudio spec (-1,1 instead of -127,127), converting to standard array in the process.
  for(i=0; i < this.samples.length; i++) {
    var temp = [];
    for(j=0; j < this.samples[i].length; j++) {
      //Remove the leading 4 bytes of the sample, which would normally be used for storing loop data in RAM, but are unneeded.
      temp[j] = this.samples[i][j+3] / 127;
    }
    this.samples[i] = temp;
  } 
}

//sample test player
function testPlay() {
  var audioCtx = modFile.context;
  console.log(modFile.proTracker.samples[sampleSel].length)
  var sampleBuffer = audioCtx.createBuffer(1, modFile.proTracker.samples[sampleSel].length, 8287); //1hz sample rate to "cheat" and reduce calculation of playback rate
  var buffering = sampleBuffer.getChannelData(0);
  for(i=0; i < modFile.proTracker.samples[sampleSel].length; i++) {
    buffering[i] = modFile.proTracker.samples[sampleSel][i];
  }
  modFile.proTracker.WAsamples[sampleSel] = sampleBuffer;
  var source = audioCtx.createBufferSource();
  source.buffer = sampleBuffer;
  source.connect(audioCtx.destination);
  source.start(0);
}