nes-js/src/Joypad.js

JavaScript NES emulator

import {Register8bit} from './Register.js';


/**
 * Standard joypad implementation.
 * Refer to https://wiki.nesdev.com/w/index.php/Standard_controller
 */
function Joypad() {
  this.register = new Register8bit();

  this.latch = 0;
  this.currentButton = 0;

  this.buttonNum = this.getButtonsNum();

  this.buttons = [];  // if buttons are being pressed.
                      // index is corresponded to Joypad.BUTTONS'
  for(var i = 0; i < this.buttonNum; i++)
    this.buttons[i] = false;
}

//

Joypad.BUTTONS = {
  A:      0,
  B:      1,
  SELECT: 2,
  START:  3,
  UP:     4,
  DOWN:   5,
  LEFT:   6,
  RIGHT:  7
};

//

Object.assign(Joypad.prototype, {
  isJoypad: true,

  //

  /**
   *
   */
  getButtonsNum: function() {
    var num = 0;
    for (var key in Joypad.BUTTONS) {
      num++;
    }
    return num;
  },

  //

  /**
   *
   */
  pressButton: function(type) {
    this.buttons[type] = true;
  },

  /**
   *
   */
  releaseButton: function(type) {
    this.buttons[type] = false;
  },

  //

  /**
   *
   */
  loadRegister: function() {
    var button = this.latch === 1 ? 0 : this.currentButton++;

    // 1: a button is being pressed or after eight reads
    // 0: otherwise
    var value = (button >= this.buttonNum || this.buttons[button]) ? 1 : 0;

    return value;
  },

  /**
   *
   */
  storeRegister: function(value) {
    this.register.store(value);

    value = value & 1;

    if (value === 1)
      this.currentButton = 0;

    this.latch = value;
  },

  // dump

  /**
   *
   */
  dump: function() {

  }
});


export {Joypad};