nes-emu/apu/synthesis/VolumeEnvelope.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _constants = _interopRequireDefault(require("../../constants"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/** A volume envelope. It starts at a volume of 15 and decrements every time the unit is clocked. */
class VolumeEnvelope {
  constructor() {
    // input
    this.startFlag = false;

    // output
    this.dividerCount = 0;
    this.volume = 0;
  }

  /** Decrements `volume` every `period` clocks. If `loop`, it resets the countdown to 15. */
  clock(period, loop) {
    if (!this.startFlag) {
      if (this.dividerCount === 0) {
        this.dividerCount = period;
        if (this.volume === 0) {
          if (loop) this.volume = _constants.default.APU_MAX_VOLUME;
        } else {
          this.volume--;
        }
      } else {
        this.dividerCount--;
      }
    } else {
      this.startFlag = false;
      this.volume = _constants.default.APU_MAX_VOLUME;
      this.dividerCount = period;
    }
  }

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

  /** Restores state from a snapshot. */
  setSaveState(saveState) {
    this.startFlag = saveState.startFlag;
    this.dividerCount = saveState.dividerCount;
    this.volume = saveState.volume;
  }
}
exports.default = VolumeEnvelope;