xm.js

(function (window) {
if (!window.XMPlayer) {
  window.XMPlayer = {};
}
var player = window.XMPlayer;

if (!window.XMView) {
  window.XMView = {};
}
var XMView = window.XMView;

player.periodForNote = periodForNote;
player.prettify_effect = prettify_effect;
player.init = init;
player.load = load;
player.play = play;
player.pause = pause;
player.stop = stop;
player.cur_songpos = -1;
player.cur_pat = -1;
player.cur_row = 64;
player.cur_ticksamp = 0;
player.cur_tick = 6;
player.xm = {};  // contains all song data
player.xm.global_volume = player.max_global_volume = 128;

// exposed for testing
player.nextTick = nextTick;
player.nextRow = nextRow;
player.Envelope = Envelope;

// for pretty-printing notes
var _note_names = [
  "C-", "C#", "D-", "D#", "E-", "F-",
  "F#", "G-", "G#", "A-", "A#", "B-"];

var f_smp = 44100;  // updated by play callback, default value here

// per-sample exponential moving average for volume changes (to prevent pops
// and clicks); evaluated every 8 samples
var popfilter_alpha = 0.9837;

function prettify_note(note) {
  if (note < 0) return "---";
  if (note == 96) return "^^^";
  return _note_names[note%12] + ~~(note/12);
}

function prettify_number(num) {
  if (num == -1) return "--";
  if (num < 10) return "0" + num;
  return num;
}

function prettify_volume(num) {
  if (num < 0x10) return "--";
  return num.toString(16);
}

function prettify_effect(t, p) {
  if (t >= 10) t = String.fromCharCode(55 + t);
  if (p < 16) p = '0' + p.toString(16);
  else p = p.toString(16);
  return t + p;
}

function prettify_notedata(data) {
  return (prettify_note(data[0]) + " " + prettify_number(data[1]) + " " +
      prettify_volume(data[2]) + " " +
      prettify_effect(data[3], data[4]));
}

function getstring(dv, offset, len) {
  var str = [];
  for (var i = offset; i < offset+len; i++) {
    var c = dv.getUint8(i);
    if (c === 0) break;
    str.push(String.fromCharCode(c));
  }
  return str.join('');
}

// Return 2-pole Butterworth lowpass filter coefficients for
// center frequncy f_c (relative to sampling frequency)
function filterCoeffs(f_c) {
  if (f_c > 0.5) {  // we can't lowpass above the nyquist frequency...
    f_c = 0.5;
  }
  var wct = Math.sqrt(2) * Math.PI * f_c;
  var e = Math.exp(-wct);
  var c = e * Math.cos(wct);
  var gain = (1 - 2*c + e*e) / 2;
  return [gain, 2*c, -e*e];
}

function updateChannelPeriod(ch, period) {
  var freq = 8363 * Math.pow(2, (1152.0 - period) / 192.0);
  if (isNaN(freq)) {
    console.log("invalid period!", period);
    return;
  }
  ch.doff = freq / f_smp;
  ch.filter = filterCoeffs(ch.doff / 2);
}

function periodForNote(ch, note) {
  return 1920 - (note + ch.samp.note)*16 - ch.fine / 8.0;
}

function setCurrentPattern() {
  var nextPat = player.xm.songpats[player.cur_songpos];

  // check for out of range pattern index
  while (nextPat >= player.xm.patterns.length) {
    if (player.cur_songpos + 1 < player.xm.songpats.length) {
      // first try skipping the position
      player.cur_songpos++;
    } else if ((player.cur_songpos === player.xm.song_looppos && player.cur_songpos !== 0)
      || player.xm.song_looppos >= player.xm.songpats.length) {
      // if we allready tried song_looppos or if song_looppos
      // is out of range, go to the first position
      player.cur_songpos = 0;
    } else {
      // try going to song_looppos
      player.cur_songpos = player.xm.song_looppos;
    }

    nextPat = player.xm.songpats[player.cur_songpos];
  }

  player.cur_pat = nextPat;
}

function nextRow() {
  if(typeof player.next_row === "undefined") { player.next_row = player.cur_row + 1; }
  player.cur_row = player.next_row;
  player.next_row++;

  if (player.cur_pat == -1 || player.cur_row >= player.xm.patterns[player.cur_pat].length) {
    player.cur_row = 0;
    player.next_row = 1;
    player.cur_songpos++;
    if (player.cur_songpos >= player.xm.songpats.length)
      player.cur_songpos = player.xm.song_looppos;
    setCurrentPattern();
  }
  var p = player.xm.patterns[player.cur_pat];
  var r = p[player.cur_row];
  for (var i = 0; i < r.length; i++) {
    var ch = player.xm.channelinfo[i];
    var inst = ch.inst;
    var triggernote = false;
    // instrument trigger
    if (r[i][1] != -1) {
      inst = player.xm.instruments[r[i][1] - 1];
      if (inst && inst.samplemap) {
        ch.inst = inst;
        // retrigger unless overridden below
        triggernote = true;
        if (ch.note && inst.samplemap) {
          ch.samp = inst.samples[inst.samplemap[ch.note]];
          ch.vol = ch.samp.vol;
          ch.pan = ch.samp.pan;
          ch.fine = ch.samp.fine;
        }
      } else {
        // console.log("invalid inst", r[i][1], instruments.length);
      }
    }

    // note trigger
    if (r[i][0] != -1) {
      if (r[i][0] == 96) {
        ch.release = 1;
        triggernote = false;
      } else {
        if (inst && inst.samplemap) {
          var note = r[i][0];
          ch.note = note;
          ch.samp = inst.samples[inst.samplemap[ch.note]];
          if (triggernote) {
            // if we were already triggering the note, reset vol/pan using
            // (potentially) new sample
            ch.pan = ch.samp.pan;
            ch.vol = ch.samp.vol;
            ch.fine = ch.samp.fine;
          }
          triggernote = true;
        }
      }
    }

    ch.voleffectfn = undefined;
    if (r[i][2] != -1) {  // volume column
      var v = r[i][2];
      ch.voleffectdata = v & 0x0f;
      if (v < 0x10) {
        console.log("channel", i, "invalid volume", v.toString(16));
      } else if (v <= 0x50) {
        ch.vol = v - 0x10;
      } else if (v >= 0x60 && v < 0x70) {  // volume slide down
        ch.voleffectfn = function(ch) {
          ch.vol = Math.max(0, ch.vol - ch.voleffectdata);
        };
      } else if (v >= 0x70 && v < 0x80) {  // volume slide up
        ch.voleffectfn = function(ch) {
          ch.vol = Math.min(64, ch.vol + ch.voleffectdata);
        };
      } else if (v >= 0x80 && v < 0x90) {  // fine volume slide down
        ch.vol = Math.max(0, ch.vol - (v & 0x0f));
      } else if (v >= 0x90 && v < 0xa0) {  // fine volume slide up
        ch.vol = Math.min(64, ch.vol + (v & 0x0f));
      } else if (v >= 0xa0 && v < 0xb0) {  // vibrato speed
        ch.vibratospeed = v & 0x0f;
      } else if (v >= 0xb0 && v < 0xc0) {  // vibrato w/ depth
        ch.vibratodepth = v & 0x0f;
        ch.voleffectfn = player.effects_t1[4];  // use vibrato effect directly
        player.effects_t1[4](ch);  // and also call it on tick 0
      } else if (v >= 0xc0 && v < 0xd0) {  // set panning
        ch.pan = (v & 0x0f) * 0x11;
      } else if (v >= 0xf0 && v <= 0xff) {  // portamento
        if (v & 0x0f) {
          ch.portaspeed = (v & 0x0f) << 4;
        }
        ch.voleffectfn = player.effects_t1[3];  // just run 3x0
      } else {
        console.log("channel", i, "volume effect", v.toString(16));
      }
    }

    ch.effect = r[i][3];
    ch.effectdata = r[i][4];
    if (ch.effect < 36) {
      ch.effectfn = player.effects_t1[ch.effect];
      var eff_t0 = player.effects_t0[ch.effect];
      if (eff_t0 && eff_t0(ch, ch.effectdata)) {
        triggernote = false;
      }
    } else {
      console.log("channel", i, "effect > 36", ch.effect);
    }

    // special handling for portamentos: don't trigger the note
    if (ch.effect == 3 || ch.effect == 5 || r[i][2] >= 0xf0) {
      if (r[i][0] != -1) {
        ch.periodtarget = periodForNote(ch, ch.note);
      }
      triggernote = false;
      if (inst && inst.samplemap) {
        if (ch.env_vol == undefined) {
          // note wasn't already playing; we basically have to ignore the
          // portamento and just trigger
          triggernote = true;
        } else if (ch.release) {
          // reset envelopes if note was released but leave offset/pitch/etc
          // alone
          ch.envtick = 0;
          ch.release = 0;
          ch.env_vol = new EnvelopeFollower(inst.env_vol);
          ch.env_pan = new EnvelopeFollower(inst.env_pan);
        }
      }
    }

    if (triggernote) {
      // there's gotta be a less hacky way to handle offset commands...
      if (ch.effect != 9) ch.off = 0;
      ch.release = 0;
      ch.envtick = 0;
      ch.env_vol = new EnvelopeFollower(inst.env_vol);
      ch.env_pan = new EnvelopeFollower(inst.env_pan);
      if (ch.note) {
        ch.period = periodForNote(ch, ch.note);
      }
      // waveforms 0-3 are retriggered on new notes while 4-7 are continuous
      if (ch.vibratotype < 4) {
        ch.vibratopos = 0;
      }
    }
  }
}

function Envelope(points, type, sustain, loopstart, loopend) {
  this.points = points;
  this.type = type;
  this.sustain = sustain;
  this.loopstart = points[loopstart*2];
  this.loopend = points[loopend*2];
}

Envelope.prototype.Get = function(ticks) {
  // TODO: optimize follower with ptr
  // or even do binary search here
  var y0;
  var env = this.points;
  for (var i = 0; i < env.length; i += 2) {
    y0 = env[i+1];
    if (ticks < env[i]) {
      var x0 = env[i-2];
      y0 = env[i-1];
      var dx = env[i] - x0;
      var dy = env[i+1] - y0;
      return y0 + (ticks - x0) * dy / dx;
    }
  }
  return y0;
};

function EnvelopeFollower(env) {
  this.env = env;
  this.tick = 0;
}

EnvelopeFollower.prototype.Tick = function(release) {
  var value = this.env.Get(this.tick);

  // if we're sustaining a note, stop advancing the tick counter
  if (!release && this.tick >= this.env.points[this.env.sustain*2]) {
    return this.env.points[this.env.sustain*2 + 1];
  }

  this.tick++;
  if (this.env.type & 4) {  // envelope loop?
    if (!release &&
        this.tick >= this.env.loopend) {
      this.tick -= this.env.loopend - this.env.loopstart;
    }
  }
  return value;
};

function nextTick() {
  player.cur_tick++;
  var j, ch;
  for (j = 0; j < player.xm.nchan; j++) {
    ch = player.xm.channelinfo[j];
    ch.periodoffset = 0;
  }
  if (player.cur_tick >= player.xm.tempo) {
    player.cur_tick = 0;
    nextRow();
  }
  for (j = 0; j < player.xm.nchan; j++) {
    ch = player.xm.channelinfo[j];
    var inst = ch.inst;
    if (player.cur_tick !== 0) {
      if(ch.voleffectfn) ch.voleffectfn(ch);
      if(ch.effectfn) ch.effectfn(ch);
    }
    if (isNaN(ch.period)) {
      console.log(prettify_notedata(
            player.xm.patterns[player.cur_pat][player.cur_row][j]),
          "set channel", j, "period to NaN");
    }
    if (inst === undefined) continue;
    if (ch.env_vol === undefined) {
      console.log(prettify_notedata(
            player.xm.patterns[player.cur_pat][player.cur_row][j]),
          "set channel", j, "env_vol to undefined, but note is playing");
      continue;
    }
    ch.volE = ch.env_vol.Tick(ch.release);
    ch.panE = ch.env_pan.Tick(ch.release);
    updateChannelPeriod(ch, ch.period + ch.periodoffset);
  }
}

// This function gradually brings the channel back down to zero if it isn't
// already to avoid clicks and pops when samples end.
function MixSilenceIntoBuf(ch, start, end, dataL, dataR) {
  var s = ch.filterstate[1];
  if (isNaN(s)) {
    console.log("NaN filterstate?", ch.filterstate, ch.filter);
    return;
  }
  for (var i = start; i < end; i++) {
    if (Math.abs(s) < 1.526e-5) {  // == 1/65536.0
      s = 0;
      break;
    }
    dataL[i] += s * ch.vL;
    dataR[i] += s * ch.vR;
    s *= popfilter_alpha;
  }
  ch.filterstate[1] = s;
  ch.filterstate[2] = s;
  if (isNaN(s)) {
    console.log("NaN filterstate after adding silence?", ch.filterstate, ch.filter, i);
    return;
  }
  return 0;
}

function MixChannelIntoBuf(ch, start, end, dataL, dataR) {
  var inst = ch.inst;
  var instsamp = ch.samp;
  var loop = false;
  var looplen = 0, loopstart = 0;

  // nothing on this channel, just filter the last dc offset back down to zero
  if (instsamp == undefined || inst == undefined || ch.mute) {
    return MixSilenceIntoBuf(ch, start, end, dataL, dataR);
  }

  var samp = instsamp.sampledata;
  var sample_end = instsamp.len;
  if ((instsamp.type & 3) == 1 && instsamp.looplen > 0) {
    loop = true;
    loopstart = instsamp.loop;
    looplen = instsamp.looplen;
    sample_end = loopstart + looplen;
  }
  var samplen = instsamp.len;
  var volE = ch.volE / 64.0;    // current volume envelope
  var panE = 4*(ch.panE - 32);  // current panning envelope
  var p = panE + ch.pan - 128;  // final pan
  var volL = player.xm.global_volume * volE * (128 - p) * ch.vol / (64 * 128 * 128);
  var volR = player.xm.global_volume * volE * (128 + p) * ch.vol / (64 * 128 * 128);
  if (volL < 0) volL = 0;
  if (volR < 0) volR = 0;
  if (volR === 0 && volL === 0)
    return;
  if (isNaN(volR) || isNaN(volL)) {
    console.log("NaN volume!?", ch.number, volL, volR, volE, panE, ch.vol);
    return;
  }
  var k = ch.off;
  var dk = ch.doff;
  var Vrms = 0;
  var f0 = ch.filter[0], f1 = ch.filter[1], f2 = ch.filter[2];
  var fs0 = ch.filterstate[0], fs1 = ch.filterstate[1], fs2 = ch.filterstate[2];

  // we also low-pass filter volume changes with a simple one-zero,
  // one-pole filter to avoid pops and clicks when volume changes.
  var vL = popfilter_alpha * ch.vL + (1 - popfilter_alpha) * (volL + ch.vLprev) * 0.5;
  var vR = popfilter_alpha * ch.vR + (1 - popfilter_alpha) * (volR + ch.vRprev) * 0.5;
  var pf_8 = Math.pow(popfilter_alpha, 8);
  ch.vLprev = volL;
  ch.vRprev = volR;

  // we can mix up to this many bytes before running into a sample end/loop
  var i = start;
  var failsafe = 100;
  while (i < end) {
    if (failsafe-- === 0) {
      console.log("failsafe in mixing loop! channel", ch.number, k, sample_end,
          loopstart, looplen, dk);
      break;
    }
    if (k >= sample_end) {  // TODO: implement pingpong looping
      if (loop) {
        k = loopstart + (k - loopstart) % looplen;
      } else {
        // kill sample
        ch.inst = undefined;
        // fill rest of buf with filtered dc offset using loop above
        return Vrms + MixSilenceIntoBuf(ch, i, end, dataL, dataR);
      }
    }
    var next_event = Math.max(1, Math.min(end, i + (sample_end - k) / dk));
    // this is the inner loop of the player

    // unrolled 8x
    var s, y;
    for (; i + 7 < next_event; i+=8) {
      s = samp[k|0];
      y = f0 * (s + fs0) + f1*fs1 + f2*fs2;
      fs2 = fs1; fs1 = y; fs0 = s;
      k += dk;
      dataL[i] += vL * y;
      dataR[i] += vR * y;
      Vrms += (vL + vR) * y * y;

      s = samp[k|0];
      y = f0 * (s + fs0) + f1*fs1 + f2*fs2;
      fs2 = fs1; fs1 = y; fs0 = s;
      k += dk;
      dataL[i+1] += vL * y;
      dataR[i+1] += vR * y;
      Vrms += (vL + vR) * y * y;

      s = samp[k|0];
      y = f0 * (s + fs0) + f1*fs1 + f2*fs2;
      fs2 = fs1; fs1 = y; fs0 = s;
      k += dk;
      dataL[i+2] += vL * y;
      dataR[i+2] += vR * y;
      Vrms += (vL + vR) * y * y;

      s = samp[k|0];
      y = f0 * (s + fs0) + f1*fs1 + f2*fs2;
      fs2 = fs1; fs1 = y; fs0 = s;
      k += dk;
      dataL[i+3] += vL * y;
      dataR[i+3] += vR * y;
      Vrms += (vL + vR) * y * y;

      s = samp[k|0];
      y = f0 * (s + fs0) + f1*fs1 + f2*fs2;
      fs2 = fs1; fs1 = y; fs0 = s;
      k += dk;
      dataL[i+4] += vL * y;
      dataR[i+4] += vR * y;
      Vrms += (vL + vR) * y * y;

      s = samp[k|0];
      y = f0 * (s + fs0) + f1*fs1 + f2*fs2;
      fs2 = fs1; fs1 = y; fs0 = s;
      k += dk;
      dataL[i+5] += vL * y;
      dataR[i+5] += vR * y;
      Vrms += (vL + vR) * y * y;

      s = samp[k|0];
      y = f0 * (s + fs0) + f1*fs1 + f2*fs2;
      fs2 = fs1; fs1 = y; fs0 = s;
      k += dk;
      dataL[i+6] += vL * y;
      dataR[i+6] += vR * y;
      Vrms += (vL + vR) * y * y;

      s = samp[k|0];
      y = f0 * (s + fs0) + f1*fs1 + f2*fs2;
      fs2 = fs1; fs1 = y; fs0 = s;
      k += dk;
      dataL[i+7] += vL * y;
      dataR[i+7] += vR * y;
      Vrms += (vL + vR) * y * y;

      vL = pf_8 * vL + (1 - pf_8) * volL;
      vR = pf_8 * vR + (1 - pf_8) * volR;
    }

    for (; i < next_event; i++) {
      s = samp[k|0];
      // we low-pass filter here since we are resampling some arbitrary
      // frequency to f_smp; this is an anti-aliasing filter and is
      // implemented as an IIR butterworth filter (usually we'd use an FIR
      // brick wall filter, but this is much simpler computationally and
      // sounds fine)
      y = f0 * (s + fs0) + f1*fs1 + f2*fs2;
      fs2 = fs1; fs1 = y; fs0 = s;
      dataL[i] += vL * y;
      dataR[i] += vR * y;
      Vrms += (vL + vR) * y * y;
      k += dk;
    }
  }
  ch.off = k;
  ch.filterstate[0] = fs0;
  ch.filterstate[1] = fs1;
  ch.filterstate[2] = fs2;
  ch.vL = vL;
  ch.vR = vR;
  return Vrms * 0.5;
}

function audio_cb(e) {
  f_smp = player.audioctx.sampleRate;
  var time_sound_started;
  var buflen = e.outputBuffer.length;
  var dataL = e.outputBuffer.getChannelData(0);
  var dataR = e.outputBuffer.getChannelData(1);
  var i, j, k;

  for (i = 0; i < buflen; i++) {
    dataL[i] = 0;
    dataR[i] = 0;
  }

  var offset = 0;
  var ticklen = 0|(f_smp * 2.5 / player.xm.bpm);
  var scopewidth = XMView.scope_width;

  while(buflen > 0) {
    if (player.cur_pat == -1 || player.cur_ticksamp >= ticklen) {
      nextTick(f_smp);
      player.cur_ticksamp -= ticklen;
    }
    var tickduration = Math.min(buflen, ticklen - player.cur_ticksamp);
    var VU = new Float32Array(player.xm.nchan);
    var scopes = undefined;
    for (j = 0; j < player.xm.nchan; j++) {
      var scope;
      if (tickduration >= 4*scopewidth) {
        scope = new Float32Array(scopewidth);
        for (k = 0; k < scopewidth; k++) {
          scope[k] = -dataL[offset+k*4] - dataR[offset+k*4];
        }
      }

      VU[j] = MixChannelIntoBuf(
          player.xm.channelinfo[j], offset, offset + tickduration, dataL, dataR) /
        tickduration;

      if (tickduration >= 4*scopewidth) {
        for (k = 0; k < scopewidth; k++) {
          scope[k] += dataL[offset+k*4] + dataR[offset+k*4];
        }
        if (scopes === undefined) scopes = [];
        scopes.push(scope);
      }
    }
    if (XMView.pushEvent) {
      XMView.pushEvent({
        t: e.playbackTime + (0.0 + offset) / f_smp,
        vu: VU,
        scopes: scopes,
        songpos: player.cur_songpos,
        pat: player.cur_pat,
        row: player.cur_row
      });
    }
    offset += tickduration;
    player.cur_ticksamp += tickduration;
    buflen -= tickduration;
  }
}

function ConvertSample(array, bits) {
  var len = array.length;
  var acc = 0;
  var samp, b, k;
  if (bits === 0) {  // 8 bit sample
    samp = new Float32Array(len);
    for (k = 0; k < len; k++) {
      acc += array[k];
      b = acc&255;
      if (b & 128) b = b-256;
      samp[k] = b / 128.0;
    }
    return samp;
  } else {
    len /= 2;
    samp = new Float32Array(len);
    for (k = 0; k < len; k++) {
      b = array[k*2] + (array[k*2 + 1] << 8);
      if (b & 32768) b = b-65536;
      acc = Math.max(-1, Math.min(1, acc + b / 32768.0));
      samp[k] = acc;
    }
    return samp;
  }
}

// optimization: unroll short sample loops so we can run our inner mixing loop
// uninterrupted for as long as possible; this also handles pingpong loops.
function UnrollSampleLoop(samp) {
  var nloops = ((2048 + samp.looplen - 1) / samp.looplen) | 0;
  var pingpong = samp.type & 2;
  if (pingpong) {
    // make sure we have an even number of loops if we are pingponging
    nloops = (nloops + 1) & (~1);
  }
  var samplesiz = samp.loop + nloops * samp.looplen;
  var data = new Float32Array(samplesiz);
  for (var i = 0; i < samp.loop; i++) {
    data[i] = samp.sampledata[i];
  }
  for (var j = 0; j < nloops; j++) {
    var k;
    if ((j&1) && pingpong) {
      for (k = samp.looplen - 1; k >= 0; k--) {
        data[i++] = samp.sampledata[samp.loop + k];
      }
    } else {
      for (k = 0; k < samp.looplen; k++) {
        data[i++] = samp.sampledata[samp.loop + k];
      }
    }
  }
  console.log("unrolled sample loop; looplen", samp.looplen, "x", nloops, " = ", samplesiz);
  samp.sampledata = data;
  samp.looplen = nloops * samp.looplen;
  samp.type = 1;
}

function load(arrayBuf) {
  var dv = new DataView(arrayBuf);
  player.xm = {};

  player.xm.songname = getstring(dv, 17, 20);
  var hlen = dv.getUint32(0x3c, true) + 0x3c;
  var songlen = dv.getUint16(0x40, true);
  player.xm.song_looppos = dv.getUint16(0x42, true);
  player.xm.nchan = dv.getUint16(0x44, true);
  var npat = dv.getUint16(0x46, true);
  var ninst = dv.getUint16(0x48, true);
  player.xm.flags = dv.getUint16(0x4a, true);
  player.xm.tempo = dv.getUint16(0x4c, true);
  player.xm.bpm = dv.getUint16(0x4e, true);
  player.xm.channelinfo = [];
  player.xm.global_volume = player.max_global_volume;

  var i, j, k;

  for (i = 0; i < player.xm.nchan; i++) {
    player.xm.channelinfo.push({
      number: i,
      filterstate: new Float32Array(3),
      vol: 0,
      pan: 128,
      period: 1920 - 48*16,
      vL: 0, vR: 0,   // left right volume envelope followers (changes per sample)
      vLprev: 0, vRprev: 0,
      mute: 0,
      volE: 0, panE: 0,
      retrig: 0,
      vibratopos: 0,
      vibratodepth: 1,
      vibratospeed: 1,
      vibratotype: 0,
    });
  }
  console.log("header len " + hlen);

  console.log("songlen %d, %d channels, %d patterns, %d instruments", songlen, player.xm.nchan, npat, ninst);
  console.log("loop @%d", player.xm.song_looppos);
  console.log("flags=%d tempo %d bpm %d", player.xm.flags, player.xm.tempo, player.xm.bpm);

  player.xm.songpats = [];
  for (i = 0; i < songlen; i++) {
    player.xm.songpats.push(dv.getUint8(0x50 + i));
  }
  console.log("song patterns: ", player.xm.songpats);

  var idx = hlen;
  player.xm.patterns = [];
  for (i = 0; i < npat; i++) {
    var pattern = [];
    var patheaderlen = dv.getUint32(idx, true);
    var patrows = dv.getUint16(idx + 5, true);
    var patsize = dv.getUint16(idx + 7, true);
    console.log("pattern %d: %d bytes, %d rows", i, patsize, patrows);
    idx += 9;
    for (j = 0; patsize > 0 && j < patrows; j++) {
      row = [];
      for (k = 0; k < player.xm.nchan; k++) {
        var byte0 = dv.getUint8(idx); idx++;
        var note = -1, inst = -1, vol = -1, efftype = 0, effparam = 0;
        if (byte0 & 0x80) {
          if (byte0 & 0x01) {
            note = dv.getUint8(idx) - 1; idx++;
          }
          if (byte0 & 0x02) {
            inst = dv.getUint8(idx); idx++;
          }
          if (byte0 & 0x04) {
            vol = dv.getUint8(idx); idx++;
          }
          if (byte0 & 0x08) {
            efftype = dv.getUint8(idx); idx++;
          }
          if (byte0 & 0x10) {
            effparam = dv.getUint8(idx); idx++;
          }
        } else {
          // byte0 is note from 1..96 or 0 for nothing or 97 for release
          // so we subtract 1 so that C-0 is stored as 0
          note = byte0 - 1;
          inst = dv.getUint8(idx); idx++;
          vol = dv.getUint8(idx); idx++;
          efftype = dv.getUint8(idx); idx++;
          effparam = dv.getUint8(idx); idx++;
        }
        var notedata = [note, inst, vol, efftype, effparam];
        row.push(notedata);
      }
      pattern.push(row);
    }
    player.xm.patterns.push(pattern);
  }

  player.xm.instruments = [];
  // now load instruments
  for (i = 0; i < ninst; i++) {
    var hdrsiz = dv.getUint32(idx, true);
    var instname = getstring(dv, idx+0x4, 22);
    var nsamp = dv.getUint16(idx+0x1b, true);
    var inst = {
      'name': instname,
      'number': i,
    };
    if (nsamp > 0) {
      var samplemap = new Uint8Array(arrayBuf, idx+33, 96);

      var env_nvol = dv.getUint8(idx+225);
      var env_vol_type = dv.getUint8(idx+233);
      var env_vol_sustain = dv.getUint8(idx+227);
      var env_vol_loop_start = dv.getUint8(idx+228);
      var env_vol_loop_end = dv.getUint8(idx+229);
      var env_npan = dv.getUint8(idx+226);
      var env_pan_type = dv.getUint8(idx+234);
      var env_pan_sustain = dv.getUint8(idx+230);
      var env_pan_loop_start = dv.getUint8(idx+231);
      var env_pan_loop_end = dv.getUint8(idx+232);
      var vol_fadeout = dv.getUint16(idx+239, true);
      var env_vol = [];
      for (j = 0; j < env_nvol*2; j++) {
        env_vol.push(dv.getUint16(idx+129+j*2, true));
      }
      var env_pan = [];
      for (j = 0; j < env_npan*2; j++) {
        env_pan.push(dv.getUint16(idx+177+j*2, true));
      }
      // FIXME: ignoring keymaps for now and assuming 1 sample / instrument
      // var keymap = getarray(dv, idx+0x21);
      var samphdrsiz = dv.getUint32(idx+0x1d, true);
      console.log("hdrsiz %d; instrument %s: '%s' %d samples, samphdrsiz %d",
          hdrsiz, (i+1).toString(16), instname, nsamp, samphdrsiz);
      idx += hdrsiz;
      var totalsamples = 0;
      var samps = [];
      for (j = 0; j < nsamp; j++) {
        var samplen = dv.getUint32(idx, true);
        var samploop = dv.getUint32(idx+4, true);
        var samplooplen = dv.getUint32(idx+8, true);
        var sampvol = dv.getUint8(idx+12);
        var sampfinetune = dv.getInt8(idx+13);
        var samptype = dv.getUint8(idx+14);
        var samppan = dv.getUint8(idx+15);
        var sampnote = dv.getInt8(idx+16);
        var sampname = getstring(dv, idx+18, 22);
        var sampleoffset = totalsamples;
        if (samplooplen === 0) {
          samptype &= ~3;
        }
        console.log("sample %d: len %d name '%s' loop %d/%d vol %d offset %s",
            j, samplen, sampname, samploop, samplooplen, sampvol, sampleoffset.toString(16));
        console.log("           type %d note %s(%d) finetune %d pan %d",
            samptype, prettify_note(sampnote + 12*4), sampnote, sampfinetune, samppan);
        console.log("           vol env", env_vol, env_vol_sustain,
            env_vol_loop_start, env_vol_loop_end, "type", env_vol_type,
            "fadeout", vol_fadeout);
        console.log("           pan env", env_pan, env_pan_sustain,
            env_pan_loop_start, env_pan_loop_end, "type", env_pan_type);
        var samp = {
          'len': samplen, 'loop': samploop,
          'looplen': samplooplen, 'note': sampnote, 'fine': sampfinetune,
          'pan': samppan, 'type': samptype, 'vol': sampvol,
          'fileoffset': sampleoffset
        };
        // length / pointers are all specified in bytes; fixup for 16-bit samples
        samps.push(samp);
        idx += samphdrsiz;
        totalsamples += samplen;
      }
      for (j = 0; j < nsamp; j++) {
        var samp = samps[j];
        samp.sampledata = ConvertSample(
            new Uint8Array(arrayBuf, idx + samp.fileoffset, samp.len), samp.type & 16);
        if (samp.type & 16) {
          samp.len /= 2;
          samp.loop /= 2;
          samp.looplen /= 2;
        }
        // unroll short loops and any pingpong loops
        if ((samp.type & 3) && (samp.looplen < 2048 || (samp.type & 2))) {
          UnrollSampleLoop(samp);
        }
      }
      idx += totalsamples;
      inst.samplemap = samplemap;
      inst.samples = samps;
      if (env_vol_type) {
        // insert an automatic fadeout to 0 at the end of the envelope
        var env_end_tick = env_vol[env_vol.length-2];
        if (!(env_vol_type & 2)) {  // if there's no sustain point, create one
          env_vol_sustain = env_vol.length / 2;
        }
        if (vol_fadeout > 0) {
          var fadeout_ticks = 65536.0 / vol_fadeout;
          env_vol.push(env_end_tick + fadeout_ticks);
          env_vol.push(0);
        }
        inst.env_vol = new Envelope(
            env_vol,
            env_vol_type,
            env_vol_sustain,
            env_vol_loop_start,
            env_vol_loop_end);
      } else {
        // no envelope, then just make a default full-volume envelope.
        // i thought this would use fadeout, but apparently it doesn't.
        inst.env_vol = new Envelope([0, 64, 1, 0], 2, 0, 0, 0);
      }
      if (env_pan_type) {
        if (!(env_pan_type & 2)) {  // if there's no sustain point, create one
          env_pan_sustain = env_pan.length / 2;
        }
        inst.env_pan = new Envelope(
            env_pan,
            env_pan_type,
            env_pan_sustain,
            env_pan_loop_start,
            env_pan_loop_end);
      } else {
        // create a default empty envelope
        inst.env_pan = new Envelope([0, 32], 0, 0, 0, 0);
      }
    } else {
      idx += hdrsiz;
      console.log("empty instrument", i, hdrsiz, idx);
    }
    player.xm.instruments.push(inst);
  }

  console.log("loaded \"" + player.xm.songname + "\"");
  return true;
}

var jsNode, gainNode;
function init() {
  if (!player.audioctx) {
    var audioContext = window.AudioContext || window.webkitAudioContext;
    player.audioctx = new audioContext();
    gainNode = player.audioctx.createGain();
    gainNode.gain.value = 0.1;  // master volume
  }
  if (player.audioctx.createScriptProcessor === undefined) {
    jsNode = player.audioctx.createJavaScriptNode(16384, 0, 2);
  } else {
    jsNode = player.audioctx.createScriptProcessor(16384, 0, 2);
  }
  jsNode.onaudioprocess = audio_cb;
  gainNode.connect(player.audioctx.destination);
}

player.playing = false;
function play() {
  if (!player.playing) {
    // put paused events back into action, if any
    if (XMView.resume) XMView.resume();
    // start playing
    jsNode.connect(gainNode);

    // hack to get iOS to play anything
    var temp_osc = player.audioctx.createOscillator();
    temp_osc.connect(player.audioctx.destination);
    !!temp_osc.start ? temp_osc.start(0) : temp_osc.noteOn(0);
    !!temp_osc.stop ? temp_osc.stop(0) : temp_osc.noteOff(0);
    temp_osc.disconnect();
  }
  player.playing = true;
}

function pause() {
  if (player.playing) {
    jsNode.disconnect(gainNode);
    if (XMView.pause) XMView.pause();
  }
  player.playing = false;
}

function stop() {
  if (player.playing) {
    jsNode.disconnect(gainNode);
    player.playing = false;
  }
  player.cur_pat = -1;
  player.cur_row = 64;
  player.cur_songpos = -1;
  player.cur_ticksamp = 0;
  player.xm.global_volume = player.max_global_volume;
  if (XMView.stop) XMView.stop();
  init();
}
})(window);