nes-emu/apu/synthesis/PulseOscillator.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _config = _interopRequireDefault(require("../../config"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
const DUTY_SEQUENCE = [[0, 1, 0, 0, 0, 0, 0, 0], [0, 1, 1, 0, 0, 0, 0, 0], [0, 1, 1, 1, 1, 0, 0, 0], [1, 0, 0, 1, 1, 1, 1, 1]];

/** A square wave generator. */
class PulseOscillator {
  constructor() {
    this.volume = 1;
    this.dutyCycle = 0;
    this._frequency = 0;
  }

  /** Generates a new sample. */
  sample(time) {
    const period = 1 / this._frequency;
    const phase = time % period;
    const step = Math.floor(phase / (period / 8));
    return DUTY_SEQUENCE[this.dutyCycle][step] * this.volume * _config.default.PULSE_CHANNEL_VOLUME;
  }

  /** Returns a snapshot of the current state. */
  getSaveState() {
    return {
      volume: this.volume,
      dutyCycle: this.dutyCycle,
      frequency: this._frequency
    };
  }

  /** Restores state from a snapshot. */
  setSaveState(saveState) {
    this.volume = saveState.volume;
    this.dutyCycle = saveState.dutyCycle;
    this.frequency = saveState.frequency;
  }

  /** Sets the frequency, but only if the change is above a minimum threshold (this sounds better). */
  set frequency(value) {
    if (Math.abs(this._frequency - value) > _config.default.MIN_FREQUENCY_CHANGE) this._frequency = value;
  }
}
exports.default = PulseOscillator;