Pen Settings

HTML

CSS

CSS Base

Vendor Prefixing

Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. If you link to another Pen, it will include the CSS from that Pen. If the preprocessor matches, it will attempt to combine them before processing.

+ add another resource

JavaScript

Babel is required to process package imports. If you need a different preprocessor remove all packages first.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

+ add another resource

Details

Privacy

Go PRO Window blinds lowered to protect code. Code Editor with window blinds (raised) and a light blub turned on.

Keep it secret; keep it safe.

Private Pens are hidden everywhere on CodePen, except to you. You can still share them and other people can see them, they just can't find them through searching or browsing.

Upgrade to PRO

Behavior

Save Automatically?

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

Format on Save

If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.

Editor Settings

Code Indentation

Want to change your Syntax Highlighting theme, Fonts and more?

Visit your global Editor Settings.

Template

Make Template?

Templates are Pens that can be used to start other Pens quickly from the create menu. The new Pen will copy all the code and settings from the template and make a new Pen (that is not a fork). You can view all of your templates, or learn more in the documentation.

Template URL

Any Pen can act as a template (even if you don't flip the toggle above) with a special URL you can use yourself or share with others. Here's this Pen's template URL:

Screenshot

Screenshots of Pens are shown in mobile browsers, RSS feeds, to users who chose images instead of iframes, and in social media sharing.

This Pen is using the default Screenshot, generated by CodePen. Upgrade to PRO to upload your own thumbnail that will be displayed on previews of this pen throughout the site and when sharing to social media.

Upgrade to PRO

HTML

              
                <div class="progress pink">
  <div class="indeterminate white"></div>
</div>
<div class="app" style="display: none;">
  <div class="sequencer">
    <div class="steps"></div>
  </div>
  <a class="regenerate btn-floating btn-large waves-effect waves-light pink darken-2 pulse">
    <i class="material-icons">refresh</i>
  </a>
  <div class="controls">
    <div class="control">
      <a class="playpause btn-floating btn-large waves-effect waves-light blue">
        <i class="material-icons play-icon">play_arrow</i>
        <i class="material-icons pause-icon" style="display: none">pause</i>
      </a>
    </div>
    <div class="control">
      <div class="input-field grey-text">
        <select id="pattern-length">
          <option>4</option>
          <option>8</option>
          <option selected>16</option>
          <option>32</option>
        </select>
        Pattern length
      </div>
    </div>
    <div class="control">
      <p class="range-field grey-text">
        <input type="range" id="tempo" min="20" max="240" value="120" step="1"> Tempo
      </p>
    </div>
    <div class="control">
      <p class="range-field grey-text">
        <input type="range" id="swing" min="0.5" max="0.7" value="0.55" step="0.05"> Swing
      </p>
    </div>
    <div class="control">
      <p class="range-field grey-text">
        <input type="range" id="temperature" class="tooltipped" min="0.5" max="2" value="1.1" step="0.1" data-tooltip="Higher temperatures will make the neural network generates wilder patterns"
               data-delay="500"> Temperature
      </p>
    </div>
  </div>
</div>
<div class="info">
  <p>This is an experimental drum machine powered by a deep neural network. To use it, define a seed pattern on the left,
    and use the &ldquo;generate&rdquo; button. A neural network will dream up a continuation to your seed pattern.</p>
  <p>Using the
    <a href="https://github.com/tensorflow/magenta/tree/master/magenta/models/drums_rnn">Drums RNN</a> (pretrained) model from
    <a href="https://magenta.tensorflow.org/">Google Magenta</a>, and
    <a href="https://deeplearnjs.org/">deeplearn.js</a> +
    <a href="https://tonejs.github.io/">Tone.js</a>.</p>
  <p>A pen by
    <a href="https://twitter.com/teropa">@teropa</a>.</p>
</div>
              
            
!

CSS

              
                html,
body,
.app {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;

  background-color: #111;
  color: white;
}

.progress {
  max-width: 30%;
  margin: 45vh auto 55vh auto;
}

.app {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;

  background: linear-gradient(to right, #010305, #131516);
}

.sequencer,
.controls {
  width: 80vw;
}
.controls {
  display: flex;
  flex-direction: row;
  justify-content: space-around;
}
.control {
  text-align: center;
}
.control input {
  margin-bottom: 20px;
}
.select-wrapper span.caret {
  color: inherit; /* Override materialize.css black */
}
.select-wrapper input.select-dropdown {
  margin-bottom: 10px;
}
.input-field {
  margin-top: 0;
}
input[type='range'] {
  border: 0;
}
input[type='range'] + .thumb {
  background-color: #2196f3;
}
input[type='range']::-webkit-slider-thumb {
  background-color: #2196f3;
}
input[type='range']::-moz-range-thumb {
  background-color: #2196f3;
}
input[type='range']::-ms-thumb {
  background-color: #2196f3;
}

.sequencer {
  position: relative;
  height: 70vh;
  margin: 20px 0;
  display: flex;
  flex-direction: row;
  perspective: 1000px;
  transform-style: preserve-3d;
}
.sequencer .legend {
  flex: 0.75;
  display: flex;
  flex-direction: column;
}
.drum-class {
  display: flex;
  align-items: center;
  justify-content: flex-start;
  margin: 2.5px;

  font-size: 12px;
  color: #999;
}
.sequencer .steps {
  flex: 9;
  display: flex;
  flex-direction: row;
}
.step {
  flex: 1;
  display: flex;
  flex-direction: column;
  transform-style: preserve-3d;
}
.steps {
  transform-style: preserve-3d;
}
.gutter {
  width: 5px;
}
.gutter.seed-marker {
  background-color: #aaa;
  margin: 0 10px;
  cursor: move;
}
.gutter.seed-marker:hover {
  background-color: white;
}
.cell {
  margin: 2.5px 0;
  background-color: rgba(100, 100, 100, 0.1);
  border: 1px solid rgba(100, 100, 100, 0.2);
  border-radius: 3px;
  z-index: 0;
  transition: background-color 0.3s ease;
}

.cell:hover {
  background-color: rgba(100, 100, 100, 0.5);
}
.step:not(.regenerating) .cell.on {
  background-color: #64b5f6;
  opacity: 1;
}

.step.seed .cell.on {
  background-color: #e91e63;
}

.regenerate {
  position: absolute;
  visibility: hidden;
  font-size: 30px;
  line-height: 56px;
}

.kick {
  flex: 2;
  margin-bottom: 10px;
}
.snare {
  flex: 1;
  margin-top: 10px;
  margin-bottom: 10px;
}
.hi-hat-closed {
  flex: 1;
  margin-top: 10px;
}
.hi-hat-open {
  flex: 1;
  margin-bottom: 10px;
}
.tom-low {
  flex: 1;
  margin-top: 10px;
}
.tom-mid {
  flex: 1;
}
.tom-high {
  flex: 1;
  margin-bottom: 10px;
}
.clap {
  flex: 1;
  margin-top: 10px;
}
.rim {
  flex: 1;
}

.info {
  max-width: 50%;
  margin: 100px auto;
  text-align: center;
}

              
            
!

JS

              
                let loader = new dl.CheckpointLoader(
  'https://teropa.info/drums_rnn_checkpoint'
);

const DRUM_CLASSES = [
  'Kick',
  'Snare',
  'Hi-hat closed',
  'Hi-hat open',
  'Tom low',
  'Tom mid',
  'Tom high',
  'Clap',
  'Rim'
];
const TIME_HUMANIZATION = 0.01;

let sampleBaseUrl = 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/969699';

let reverb = new Tone.Convolver(
  `${sampleBaseUrl}/small-drum-room.wav`
).toMaster();
reverb.wet.value = 0.35;

let snarePanner = new Tone.Panner().connect(reverb);
new Tone.LFO(0.13, -0.25, 0.25).connect(snarePanner.pan).start();

let drumKit = [
  new Tone.Players({
    high: `${sampleBaseUrl}/808-kick-vh.mp3`,
    med: `${sampleBaseUrl}/808-kick-vm.mp3`,
    low: `${sampleBaseUrl}/808-kick-vl.mp3`
  }).toMaster(),
  new Tone.Players({
    high: `${sampleBaseUrl}/flares-snare-vh.mp3`,
    med: `${sampleBaseUrl}/flares-snare-vm.mp3`,
    low: `${sampleBaseUrl}/flares-snare-vl.mp3`
  }).connect(snarePanner),
  new Tone.Players({
    high: `${sampleBaseUrl}/808-hihat-vh.mp3`,
    med: `${sampleBaseUrl}/808-hihat-vm.mp3`,
    low: `${sampleBaseUrl}/808-hihat-vl.mp3`
  }).connect(new Tone.Panner(-0.5).connect(reverb)),
  new Tone.Players({
    high: `${sampleBaseUrl}/808-hihat-open-vh.mp3`,
    med: `${sampleBaseUrl}/808-hihat-open-vm.mp3`,
    low: `${sampleBaseUrl}/808-hihat-open-vl.mp3`
  }).connect(new Tone.Panner(-0.5).connect(reverb)),
  new Tone.Players({
    high: `${sampleBaseUrl}/slamdam-tom-low-vh.mp3`,
    med: `${sampleBaseUrl}/slamdam-tom-low-vm.mp3`,
    low: `${sampleBaseUrl}/slamdam-tom-low-vl.mp3`
  }).connect(new Tone.Panner(-0.4).connect(reverb)),
  new Tone.Players({
    high: `${sampleBaseUrl}/slamdam-tom-mid-vh.mp3`,
    med: `${sampleBaseUrl}/slamdam-tom-mid-vm.mp3`,
    low: `${sampleBaseUrl}/slamdam-tom-mid-vl.mp3`
  }).connect(reverb),
  new Tone.Players({
    high: `${sampleBaseUrl}/slamdam-tom-high-vh.mp3`,
    med: `${sampleBaseUrl}/slamdam-tom-high-vm.mp3`,
    low: `${sampleBaseUrl}/slamdam-tom-high-vl.mp3`
  }).connect(new Tone.Panner(0.4).connect(reverb)),
  new Tone.Players({
    high: `${sampleBaseUrl}/909-clap-vh.mp3`,
    med: `${sampleBaseUrl}/909-clap-vm.mp3`,
    low: `${sampleBaseUrl}/909-clap-vl.mp3`
  }).connect(new Tone.Panner(0.5).connect(reverb)),
  new Tone.Players({
    high: `${sampleBaseUrl}/909-rim-vh.wav`,
    med: `${sampleBaseUrl}/909-rim-vm.wav`,
    low: `${sampleBaseUrl}/909-rim-vl.wav`
  }).connect(new Tone.Panner(0.5).connect(reverb))
];

let attentionLength = 32;
let attentionSize = 256;
let dropoutKeepProb = dl.Scalar.new(1.0);
let temperature = dl.variable(dl.Scalar.new(1.2));

/*
 * Magenta's model encodes each timestep as a one-hot vector of length 512.
 * There are 9 drum classes, and any combination of those 9 classes can play simultaneously.
 * Each of the 2^9 = 512 possible combinations has its own element in the vector.
 * 
 * The one-hot vector is then augmented with six meter-tracking bits, implemented as binary counters.
 */

function encodeDrums(drumClasses, nextPosition) {
  let hotIndex = 0;
  for (let drumClass of drumClasses) {
    hotIndex += 2 ** drumClass;
  }
  let vector = _.times(2 ** DRUM_CLASSES.length, () => 0);
  vector[hotIndex] = 1;

  for (let i = 0; i < 6; i++) {
    vector.push(Math.floor(nextPosition / 2 ** i) % 2 ? 1.0 : -1.0);
  }

  return vector;
}

function decodeDrums(index) {
  let bin = (index >>> 0).toString(2);
  let drums = [];
  for (let i = bin.length - 1; i >= 0; i--) {
    if (bin[i] === '1') {
      drums.push(bin.length - i - 1);
    }
  }
  return drums;
}

Promise.all([
  loader.getAllVariables(),
  new Promise(res => Tone.Buffer.on('load', res))
]).then(([vars]) => {
  let prefix = 'RNN/AttentionCellWrapper/';
  let lstm = {
    attnInputMatrix: vars[`${prefix}Linear/Matrix`],
    attnInputBias: vars[`${prefix}Linear/Bias`].as2D(1, -1),
    attnW: vars[`${prefix}Attention/AttnW`],
    attnV: vars[`${prefix}Attention/AttnV`],
    attnMatrix: vars[`${prefix}Attention/Linear/Matrix`],
    attnBias: vars[`${prefix}Attention/Linear/Bias`],
    attnOutputMatrix: vars[`${prefix}AttnOutputProjection/Linear/Matrix`],
    attnOutputBias: vars[`${prefix}AttnOutputProjection/Linear/Bias`],
    kernel1: vars[`${prefix}MultiRNNCell/Cell0/BasicLSTMCell/Linear/Matrix`],
    bias1: vars[`${prefix}MultiRNNCell/Cell0/BasicLSTMCell/Linear/Bias`],
    kernel2: vars[`${prefix}MultiRNNCell/Cell1/BasicLSTMCell/Linear/Matrix`],
    bias2: vars[`${prefix}MultiRNNCell/Cell1/BasicLSTMCell/Linear/Bias`],
    kernel3: vars[`${prefix}MultiRNNCell/Cell2/BasicLSTMCell/Linear/Matrix`],
    bias3: vars[`${prefix}MultiRNNCell/Cell2/BasicLSTMCell/Linear/Bias`],
    fullyConnectedBiases: vars['fully_connected/biases'],
    fullyConnectedWeights: vars['fully_connected/weights']
  };

  function initNnState() {
    return {
      lstmStates: [
        dl.Array2D.zeros([1, lstm.bias1.shape[0] / 4]),
        dl.Array2D.zeros([1, lstm.bias2.shape[0] / 4]),
        dl.Array2D.zeros([1, lstm.bias3.shape[0] / 4])
      ],
      lstmOutputs: [
        dl.Array2D.zeros([1, lstm.bias1.shape[0] / 4]),
        dl.Array2D.zeros([1, lstm.bias2.shape[0] / 4]),
        dl.Array2D.zeros([1, lstm.bias3.shape[0] / 4])
      ],
      attention: dl.Array1D.zeros([attentionSize]),
      attentionState: dl.Array2D.zeros([1, attentionSize * attentionLength])
    };
  }

  function disposeNnState(state) {
    state.lstmStates.forEach(s => s.dispose());
    state.lstmOutputs.forEach(s => s.dispose());
    state.attention.dispose();
    state.attentionState.dispose();
  }

  function generateStep(
    drumClasses,
    nextPosition,
    { lstmStates, lstmOutputs, attention, attentionState }
  ) {
    return dl.tidy(async () => {
      let lstm1 = dl.basicLSTMCell.bind(
        dl,
        dropoutKeepProb,
        lstm.kernel1,
        lstm.bias1
      );
      let lstm2 = dl.basicLSTMCell.bind(
        dl,
        dropoutKeepProb,
        lstm.kernel2,
        lstm.bias2
      );
      let lstm3 = dl.basicLSTMCell.bind(
        dl,
        dropoutKeepProb,
        lstm.kernel3,
        lstm.bias3
      );

      let input = dl.Array1D.new(encodeDrums(drumClasses, nextPosition));
      let attnStates = attentionState.reshape([
        -1,
        attentionLength,
        attentionSize
      ]);

      // Apply attention to input

      let rnnInput = dl.add(
        dl.matMul(
          dl.concat([input, attention]).as2D(1, -1),
          lstm.attnInputMatrix
        ),
        lstm.attnInputBias
      );

      // LSTM

      let [newLstmStates, newLstmOutputs] = dl.multiRNNCell(
        [lstm1, lstm2, lstm3],
        rnnInput,
        lstmStates,
        lstmOutputs
      );

      // Attention

      let attnHidden = dl.reshape(attentionState, [
        -1,
        attentionLength,
        1,
        attentionSize
      ]);

      let attnHiddenFeatures = dl.conv2d(
        attnHidden,
        lstm.attnW,
        [1, 1],
        'same'
      );

      let attnQuery = dl.concat(
        [
          newLstmStates[0],
          newLstmOutputs[0],
          newLstmStates[1],
          newLstmOutputs[1],
          newLstmStates[2],
          newLstmOutputs[2]
        ],
        1
      );

      let attnY = dl
        .matMul(attnQuery, lstm.attnMatrix)
        .reshape([-1, 1, 1, attentionSize]);
      let attnS = dl.sum(
        dl.mul(lstm.attnV, dl.tanh(dl.add(attnHiddenFeatures, attnY))),
        [2, 3]
      );
      let attnA = dl.softmax(attnS);
      let attnD = dl.sum(
        dl.mul(dl.reshape(attnA, [-1, attentionLength, 1, 1]), attnHidden),
        [1, 2]
      );
      let newAttns = attnD.reshape([-1, attentionSize]);

      // Remove first (oldest) attention state
      let newAttnStates = dl.slice(
        attnStates,
        [0, 1, 0],
        [attnStates.shape[0], attnStates.shape[1] - 1, attnStates.shape[2]]
      );

      // Output projection

      let newOutput = dl.add(
        dl.matMul(
          dl.concat([newLstmOutputs[2], newAttns], 1),
          lstm.attnOutputMatrix
        ),
        lstm.attnOutputBias
      );

      // Add latest output to attention state
      newAttnStates = dl
        .concat(
          [
            newAttnStates,
            newOutput.as3D(newOutput.shape[0], 1, newOutput.shape[1])
          ],
          1
        )
        .reshape([-1, attentionLength * attentionSize]);

      lstmStates.forEach(s => s.dispose());
      lstmOutputs.forEach(o => o.dispose());
      attention.dispose();
      attentionState.dispose();
      lstmStates = newLstmStates;
      lstmOutputs = newLstmOutputs;
      attention = newAttns.flatten();
      attentionState = newAttnStates;
      lstmStates.forEach(s => dl.keep(s));
      lstmOutputs.forEach(o => dl.keep(o));
      dl.keep(attention);
      dl.keep(attentionState);

      let weightedResult = dl.matMul(newOutput, lstm.fullyConnectedWeights);
      let logits = dl.add(weightedResult, lstm.fullyConnectedBiases);
      let softmax = dl.softmax(dl.div(logits.as1D(), temperature));
      let sampledOutput = dl.ENV.math.multinomial(softmax, 1).asScalar();
      return {
        drums: decodeDrums(await sampledOutput.val()),
        nnState: { lstmStates, lstmOutputs, attention, attentionState }
      };
    });
  }

  let patternLength = 16,
    seedLength = 4,
    swing = 0.55,
    stepEls = [],
    pattern = [[0], [], [2]].concat(_.times(patternLength - 3, i => [])),
    hasBeenStarted = false,
    sequence;

  function generatePattern(
    result,
    fromStep = 0,
    currentStep = 0,
    nnState = initNnState()
  ) {
    let nextStep = currentStep + 1;
    return generateStep(result[currentStep], nextStep, nnState).then(
      ({ drums, nnState }) => {
        if (nextStep >= fromStep) {
          result[nextStep] = drums;
        }
        if (nextStep < patternLength - 1) {
          return generatePattern(result, fromStep, nextStep, nnState);
        } else {
          disposeNnState(nnState);
          return result;
        }
      }
    );
  }

  function getStepVelocity(step) {
    if (step % 4 === 0) {
      return 'high';
    } else if (step % 2 === 0) {
      return 'med';
    } else {
      return 'low';
    }
  }

  function humanizeTime(time) {
    return time - TIME_HUMANIZATION / 2 + Math.random() * TIME_HUMANIZATION;
  }

  function playPattern() {
    sequence = new Tone.Sequence(
      (time, { drums, stepIdx }) => {
        let isSwung = stepIdx % 2 !== 0;
        if (isSwung) {
          time += (swing - 0.5) * Tone.Time('8n').toSeconds();
        }
        let velocity = getStepVelocity(stepIdx);
        drums.forEach(d => {
          let humanizedTime = stepIdx === 0 ? time : humanizeTime(time);
          drumKit[d].get(velocity).start(humanizedTime);
          visualizePlay(humanizedTime, stepIdx, d);
        });
      },
      pattern.map((drums, stepIdx) => ({ drums, stepIdx })),
      '16n'
    ).start();
  }

  function visualizePlay(time, stepIdx, drumIdx) {
    Tone.Draw.schedule(() => {
      if (!stepEls[stepIdx]) return;
      let animTime = Tone.Time('2n').toMilliseconds();
      let cellEl = stepEls[stepIdx].cellEls[drumIdx];
      if (cellEl.classList.contains('on')) {
        let baseColor = stepIdx < seedLength ? '#e91e63' : '#64b5f6';
        cellEl.animate(
          [
            {
              transform: 'translateZ(-100px)',
              backgroundColor: '#fad1df'
            },
            {
              transform: 'translateZ(50px)',
              offset: 0.7
            },
            { transform: 'translateZ(0)', backgroundColor: baseColor }
          ],
          { duration: animTime, easing: 'cubic-bezier(0.23, 1, 0.32, 1)' }
        );
      }
    }, time);
  }

  function renderPattern(regenerating = false) {
    let seqEl = document.querySelector('.sequencer .steps');
    while (stepEls.length > pattern.length) {
      let { stepEl, gutterEl } = stepEls.pop();
      stepEl.remove();
      if (gutterEl) gutterEl.remove();
    }
    for (let stepIdx = 0; stepIdx < pattern.length; stepIdx++) {
      let step = pattern[stepIdx];
      let stepEl, gutterEl, cellEls;
      if (stepEls[stepIdx]) {
        stepEl = stepEls[stepIdx].stepEl;
        gutterEl = stepEls[stepIdx].gutterEl;
        cellEls = stepEls[stepIdx].cellEls;
      } else {
        stepEl = document.createElement('div');
        stepEl.classList.add('step');
        stepEl.dataset.stepIdx = stepIdx;
        seqEl.appendChild(stepEl);
        cellEls = [];
      }

      stepEl.style.flex = stepIdx % 2 === 0 ? swing : 1 - swing;

      if (!gutterEl && stepIdx < pattern.length - 1) {
        gutterEl = document.createElement('div');
        gutterEl.classList.add('gutter');
        seqEl.insertBefore(gutterEl, stepEl.nextSibling);
      } else if (gutterEl && stepIdx >= pattern.length) {
        gutterEl.remove();
        gutterEl = null;
      }

      if (gutterEl && stepIdx === seedLength - 1) {
        gutterEl.classList.add('seed-marker');
      } else if (gutterEl) {
        gutterEl.classList.remove('seed-marker');
      }

      for (let cellIdx = 0; cellIdx < DRUM_CLASSES.length; cellIdx++) {
        let cellEl;
        if (cellEls[cellIdx]) {
          cellEl = cellEls[cellIdx];
        } else {
          cellEl = document.createElement('div');
          cellEl.classList.add('cell');
          cellEl.classList.add(_.kebabCase(DRUM_CLASSES[cellIdx]));
          cellEl.dataset.stepIdx = stepIdx;
          cellEl.dataset.cellIdx = cellIdx;
          stepEl.appendChild(cellEl);
          cellEls[cellIdx] = cellEl;
        }
        if (step.indexOf(cellIdx) >= 0) {
          cellEl.classList.add('on');
        } else {
          cellEl.classList.remove('on');
        }
      }
      stepEls[stepIdx] = { stepEl, gutterEl, cellEls };

      let stagger = stepIdx * (300 / (patternLength - seedLength));
      setTimeout(() => {
        if (stepIdx < seedLength) {
          stepEl.classList.add('seed');
        } else {
          stepEl.classList.remove('seed');
          if (regenerating) {
            stepEl.classList.add('regenerating');
          } else {
            stepEl.classList.remove('regenerating');
          }
        }
      }, stagger);
    }

    setTimeout(repositionRegenerateButton, 0);
  }

  function repositionRegenerateButton() {
    let regenButton = document.querySelector('.regenerate');
    let sequencerEl = document.querySelector('.sequencer');
    let seedMarkerEl = document.querySelector('.gutter.seed-marker');
    let regenLeft =
      sequencerEl.offsetLeft +
      seedMarkerEl.offsetLeft +
      seedMarkerEl.offsetWidth / 2 -
      regenButton.offsetWidth / 2;
    let regenTop =
      sequencerEl.offsetTop +
      seedMarkerEl.offsetTop +
      seedMarkerEl.offsetHeight / 2 -
      regenButton.offsetHeight / 2;
    regenButton.style.left = `${regenLeft}px`;
    regenButton.style.top = `${regenTop}px`;
    regenButton.style.visibility = 'visible';
  }

  function regenerate() {
    let result = _.take(pattern, seedLength).concat(
      _.times(length - seedLength, () => [])
    );
    renderPattern(true);
    return generatePattern(result, seedLength).then(result => {
      pattern = result;
      onPatternUpdated();
    });
  }

  function onPatternUpdated() {
    if (sequence) {
      sequence.dispose();
      sequence = null;
    }
    renderPattern();
  }

  function toggleStep(cellEl) {
    if (pattern && cellEl.classList.contains('cell')) {
      let stepIdx = +cellEl.dataset.stepIdx;
      let cellIdx = +cellEl.dataset.cellIdx;
      let isOn = cellEl.classList.contains('on');
      if (isOn) {
        _.pull(pattern[stepIdx], cellIdx);
        cellEl.classList.remove('on');
      } else {
        pattern[stepIdx].push(cellIdx);
        cellEl.classList.add('on');
      }
      sequence.at(stepIdx, { stepIdx, drums: pattern[stepIdx] });
    }
  }

  function setSwing(newSwing) {
    swing = newSwing;
    renderPattern();
  }

  function setPatternLength(newPatternLength) {
    if (newPatternLength < patternLength) {
      pattern.length = newPatternLength;
    } else {
      for (let i = pattern.length; i < newPatternLength; i++) {
        pattern.push([]);
      }
    }
    let lengthRatio = newPatternLength / patternLength;
    seedLength = Math.max(
      1,
      Math.min(newPatternLength - 1, Math.round(seedLength * lengthRatio))
    );
    patternLength = newPatternLength;
    onPatternUpdated();
    if (Tone.Transport.state === 'started') {
      playPattern();
    }
  }

  function updatePlayPauseIcons() {
    if (Tone.Transport.state === 'started') {
      document.querySelector('.playpause .pause-icon').style.display = null;
      document.querySelector('.playpause .play-icon').style.display = 'none';
    } else {
      document.querySelector('.playpause .play-icon').style.display = null;
      document.querySelector('.playpause .pause-icon').style.display = 'none';
    }
  }

  document.querySelector('.app').addEventListener('click', event => {
    if (event.target.classList.contains('cell')) {
      toggleStep(event.target);
    }
  });
  document.querySelector('.regenerate').addEventListener('click', event => {
    event.currentTarget.classList.remove('pulse');
    regenerate().then(() => {
      if (!hasBeenStarted) {
        Tone.context.resume();
        Tone.Transport.start();
        updatePlayPauseIcons();
        hasBeenStarted = true;
      }
      if (Tone.Transport.state === 'started') {
        playPattern();
      }
    });
  });
  document.querySelector('.playpause').addEventListener('click', event => {
    if (Tone.Transport.state !== 'started') {
      Tone.context.resume();
      Tone.Transport.start();
      playPattern();
      updatePlayPauseIcons();
      hasBeenStarted = true;
    } else {
      if (sequence) {
        sequence.dispose();
        sequence = null;
      }
      Tone.Transport.pause();
      updatePlayPauseIcons();
    }
  });

  let draggingSeedMarker = false;
  document.querySelector('.app').addEventListener('mousedown', evt => {
    let el = evt.target;
    if (
      el.classList.contains('gutter') &&
      el.classList.contains('seed-marker')
    ) {
      draggingSeedMarker = true;
      evt.preventDefault();
    }
  });
  document.querySelector('.app').addEventListener('mouseup', () => {
    draggingSeedMarker = false;
  });
  document.querySelector('.app').addEventListener('mouseover', evt => {
    if (draggingSeedMarker) {
      let el = evt.target;
      while (el) {
        if (el.classList.contains('step')) {
          let stepIdx = +el.dataset.stepIdx;
          if (stepIdx > 0) {
            seedLength = stepIdx;
            renderPattern();
          }
          break;
        }
        el = el.parentElement;
      }
    }
  });
  document
    .querySelector('#swing')
    .addEventListener('input', evt => setSwing(+evt.target.value));
  document
    .querySelector('#temperature')
    .addEventListener('input', evt =>
      temperature.assign(dl.scalar(+evt.target.value))
    );
  document
    .querySelector('#pattern-length')
    .addEventListener('change', evt => setPatternLength(+evt.target.value));
  document
    .querySelector('#tempo')
    .addEventListener(
      'input',
      evt => (Tone.Transport.bpm.value = +evt.target.value)
    );

  $('select')
    .on('change', evt => setPatternLength(+evt.target.value))
    .material_select();

  window.addEventListener('resize', repositionRegenerateButton);

  renderPattern();

  document.querySelector('.progress').remove();
  document.querySelector('.app').style.display = null;
});

              
            
!
999px
Who's loopier? A fruit loop or a for loop?

Console