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 APU_SAMPLE_RATE = 44100;
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.frequency = 0;
    this._phase = 0; // (0~1)
  }

  /** Generates a new sample. */
  sample(isNewSample) {
    if (isNewSample) this._phase = (this._phase + this.frequency / APU_SAMPLE_RATE) % 1;
    const step = Math.floor(this._phase * TRIANGLE_SEQUENCE.length);
    return TRIANGLE_SEQUENCE[step] * _config.default.TRIANGLE_CHANNEL_VOLUME;
  }

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

  /** Restores state from a snapshot. */
  setSaveState(saveState) {
    this.frequency = saveState.frequency;
    this._phase = saveState.phase;
  }
}
exports.default = TriangleOscillator;