strudel/packages/superdough/ola-processor.js

'use strict';

// sourced from https://github.com/olvb/phaze/tree/master?tab=readme-ov-file
const WEBAUDIO_BLOCK_SIZE = 128;

/** Overlap-Add Node */
class OLAProcessor extends AudioWorkletProcessor {
  constructor(options) {
    super(options);
    this.started = false;
    this.nbInputs = options.numberOfInputs;
    this.nbOutputs = options.numberOfOutputs;

    this.blockSize = options.processorOptions.blockSize;
    // TODO for now, the only support hop size is the size of a web audio block
    this.hopSize = WEBAUDIO_BLOCK_SIZE;

    this.nbOverlaps = this.blockSize / this.hopSize;

    // pre-allocate input buffers (will be reallocated if needed)
    this.inputBuffers = new Array(this.nbInputs);
    this.inputBuffersHead = new Array(this.nbInputs);
    this.inputBuffersToSend = new Array(this.nbInputs);
    // default to 1 channel per input until we know more
    for (let i = 0; i < this.nbInputs; i++) {
      this.allocateInputChannels(i, 1);
    }
    // pre-allocate input buffers (will be reallocated if needed)
    this.outputBuffers = new Array(this.nbOutputs);
    this.outputBuffersToRetrieve = new Array(this.nbOutputs);
    // default to 1 channel per output until we know more
    for (let i = 0; i < this.nbOutputs; i++) {
      this.allocateOutputChannels(i, 1);
    }
  }

  /** Handles dynamic reallocation of input/output channels buffer
     (channel numbers may lety during lifecycle) **/
  reallocateChannelsIfNeeded(inputs, outputs) {
    for (let i = 0; i < this.nbInputs; i++) {
      let nbChannels = inputs[i].length;
      if (nbChannels != this.inputBuffers[i].length) {
        this.allocateInputChannels(i, nbChannels);
      }
    }

    for (let i = 0; i < this.nbOutputs; i++) {
      let nbChannels = outputs[i].length;
      if (nbChannels != this.outputBuffers[i].length) {
        this.allocateOutputChannels(i, nbChannels);
      }
    }
  }

  allocateInputChannels(inputIndex, nbChannels) {
    // allocate input buffers

    this.inputBuffers[inputIndex] = new Array(nbChannels);
    for (let i = 0; i < nbChannels; i++) {
      this.inputBuffers[inputIndex][i] = new Float32Array(this.blockSize + WEBAUDIO_BLOCK_SIZE);
      this.inputBuffers[inputIndex][i].fill(0);
    }

    // allocate input buffers to send and head pointers to copy from
    // (cannot directly send a pointer/subarray because input may be modified)
    this.inputBuffersHead[inputIndex] = new Array(nbChannels);
    this.inputBuffersToSend[inputIndex] = new Array(nbChannels);
    for (let i = 0; i < nbChannels; i++) {
      this.inputBuffersHead[inputIndex][i] = this.inputBuffers[inputIndex][i].subarray(0, this.blockSize);
      this.inputBuffersToSend[inputIndex][i] = new Float32Array(this.blockSize);
    }
  }

  allocateOutputChannels(outputIndex, nbChannels) {
    // allocate output buffers
    this.outputBuffers[outputIndex] = new Array(nbChannels);
    for (let i = 0; i < nbChannels; i++) {
      this.outputBuffers[outputIndex][i] = new Float32Array(this.blockSize);
      this.outputBuffers[outputIndex][i].fill(0);
    }

    // allocate output buffers to retrieve
    // (cannot send a pointer/subarray because new output has to be add to exising output)
    this.outputBuffersToRetrieve[outputIndex] = new Array(nbChannels);
    for (let i = 0; i < nbChannels; i++) {
      this.outputBuffersToRetrieve[outputIndex][i] = new Float32Array(this.blockSize);
      this.outputBuffersToRetrieve[outputIndex][i].fill(0);
    }
  }

  /** Read next web audio block to input buffers **/
  readInputs(inputs) {
    // when playback is paused, we may stop receiving new samples
    if (inputs[0].length && inputs[0][0].length == 0) {
      for (let i = 0; i < this.nbInputs; i++) {
        for (let j = 0; j < this.inputBuffers[i].length; j++) {
          this.inputBuffers[i][j].fill(0, this.blockSize);
        }
      }
      return;
    }

    for (let i = 0; i < this.nbInputs; i++) {
      for (let j = 0; j < this.inputBuffers[i].length; j++) {
        let webAudioBlock = inputs[i][j];
        this.inputBuffers[i][j].set(webAudioBlock, this.blockSize);
      }
    }
  }

  /** Write next web audio block from output buffers **/
  writeOutputs(outputs) {
    for (let i = 0; i < this.nbInputs; i++) {
      for (let j = 0; j < this.inputBuffers[i].length; j++) {
        let webAudioBlock = this.outputBuffers[i][j].subarray(0, WEBAUDIO_BLOCK_SIZE);
        outputs[i][j].set(webAudioBlock);
      }
    }
  }

  /** Shift left content of input buffers to receive new web audio block **/
  shiftInputBuffers() {
    for (let i = 0; i < this.nbInputs; i++) {
      for (let j = 0; j < this.inputBuffers[i].length; j++) {
        this.inputBuffers[i][j].copyWithin(0, WEBAUDIO_BLOCK_SIZE);
      }
    }
  }

  /** Shift left content of output buffers to receive new web audio block **/
  shiftOutputBuffers() {
    for (let i = 0; i < this.nbOutputs; i++) {
      for (let j = 0; j < this.outputBuffers[i].length; j++) {
        this.outputBuffers[i][j].copyWithin(0, WEBAUDIO_BLOCK_SIZE);
        this.outputBuffers[i][j].subarray(this.blockSize - WEBAUDIO_BLOCK_SIZE).fill(0);
      }
    }
  }

  /** Copy contents of input buffers to buffer actually sent to process **/
  prepareInputBuffersToSend() {
    for (let i = 0; i < this.nbInputs; i++) {
      for (let j = 0; j < this.inputBuffers[i].length; j++) {
        this.inputBuffersToSend[i][j].set(this.inputBuffersHead[i][j]);
      }
    }
  }

  /** Add contents of output buffers just processed to output buffers **/
  handleOutputBuffersToRetrieve() {
    for (let i = 0; i < this.nbOutputs; i++) {
      for (let j = 0; j < this.outputBuffers[i].length; j++) {
        for (let k = 0; k < this.blockSize; k++) {
          this.outputBuffers[i][j][k] += this.outputBuffersToRetrieve[i][j][k] / this.nbOverlaps;
        }
      }
    }
  }

  process(inputs, outputs, params) {
    const input = inputs[0];
    const hasInput = !(input[0] === undefined);
    if (this.started && !hasInput) {
      return false;
    }
    this.started = hasInput;
    this.reallocateChannelsIfNeeded(inputs, outputs);

    this.readInputs(inputs);
    this.shiftInputBuffers();
    this.prepareInputBuffersToSend();
    this.processOLA(this.inputBuffersToSend, this.outputBuffersToRetrieve, params);
    this.handleOutputBuffersToRetrieve();
    this.writeOutputs(outputs);
    this.shiftOutputBuffers();

    return true;
  }

  processOLA(inputs, outputs, params) {
    console.assert(false, 'Not overriden');
  }
}

export default OLAProcessor;