nes-emu/apu/synthesis/TriangleOscillator.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 TRIANGLE_SEQUENCE = [15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];

/** A triangle wave generator. */
class TriangleOscillator {
  constructor() {
    this.amplitude = 1;
    this._frequency = 0;
  }

  /** Generates a new sample. */
  sample(time) {
    const period = 1 / this._frequency;
    const phase = time % period;
    const step = Math.floor(phase / (period / 32));
    return TRIANGLE_SEQUENCE[step] * _config.default.TRIANGLE_CHANNEL_VOLUME;
  }

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

  /** Restores state from a snapshot. */
  setSaveState(saveState) {
    this.amplitude = saveState.amplitude;
    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 = TriangleOscillator;